Sunday, December 5, 2010

Arsenic Bacteria

Well I guess my science education hasn't been as good as I thought; last Thursday it was reviled that a bacteria had been evolved in a lab that swaps arsenic for phosphorus. The media is hailing the as rewriting the building blocks of life as we know it. I feel like I should have learned how essential the building blocks of life are, unless it turns out they're not really that essential.

First off, on Wednesday morning I read that NASA was going to have a press release about alien life. So I was hoping for so news from deep space, not from earth. This bacteria not extraterrestrial at all!

The building blocks of life are considered to be oxygen, carbon, hydrogen, nitrogen, sulfur, and phosphorus. My question lies with anaerobic organisms. What role does oxygen play for them? Bacteria have been discovered that use arsenic instead of oxygen (though this is a very different process than replacing phosphorus with arsenic; phosphorus is a key component in the structure of DNA). So is oxygen considered a building block for anaerobic organisms? My intro-level biology course has me believing it isn't. Also, a google search of oxygen and anaerobic bacteria turns up mostly results of anaerobic bacteria not needing oxygen at all (but little is mentioned on if and how oxygen in any of its forms plays a role in their structure).

To anaerobes, oxygen gas can be lethal. However, oxygen is also a key part of water (H20),  and anaerobic organisms can live in it. The bacteria were originally found in a lake before being artificially introduced into a phosphorus free environment and forced to die or survive on arsenic. The individual bacteria grew larger, and more hollow. I find the increase in size unsurprising, since arsenic has a larger radius than phosphorus.

Let's consult our periodic tables. Phosphorus and arsenic are Group V elements (as is nitrogen), so they are similar in structure, but arsenic is bigger than nitrogen or phosphorus. Interestingly all the building blocks are non-metals while arsenic is a metalloid, that's about the most interesting thing that I've gathered from this.

Come on NASA, this is not alien life. This is some bacteria artificially induced into using arsenic. Bring me some silicon based lifeforms and then we'll talk.

We are too narrow in our idea of what life can be. Research in the past has been aimed at looking for environments similar to earth (hence looking for those building blocks) on other planets. But should we really be expecting extraterrestrial life to have evolved along the same path that life here has? Sure, all Earth life is built on DNA, but that isn't the universal code it's portrayed as (it's not even totally consistent in all discovered life). Can we expand our imaginations beyond looking for DNA based organisms? If our origin of life turns out to be earth based, the chances of other planets having an identical path of evolution is infinitely small. With research like this we're already showing that life isn't as strictly controlled as once believed. Will we even recognize extraterrestrial life if/when we find it? My expectation is that on the minute chance that any alien life is ever discovered in my lifetime (and I'm giving myself at about 60 more years) that it won't look like anything we know or could have imagined possible on earth.

Thursday, December 2, 2010

Sexual Selection and Parental Investment

The concepts presented are from discussions in two anthropology courses: Bio-Cultural Evolution taught by Dr. J. Kurland in Spring 2009 and The Evolution of Human Mating taught by Dr. D. Puts in Spring 2010, both at the Pennsylvania State University.

Parental investment in animals is the degree of care that a parent puts into it's offspring. For some species this may be carrying young to term, sitting on eggs, rearing young to adulthood, etc. Generally, the females of a species has a higher parental investment than males. In many species, males only contribute their sperm, which is low in parental investment. Sperm is practically an unlimited resource, whereas in some species eggs are limited, and energy costly to produce because they are such large cells.

Species with low parental investment generally create more progeny than those with high parental investment. When parental investment is different between the sexes, the sex that invests more is known as the slow sex (because they must go longer between matings due to their investment). Again, because females tend to invest more they are usually the slow sex. Due to the energy and time costs of their parental investment, the slower sex is the choosier sex; if the degree of parental investment is going to be high, the choosy sex will want to find the best genetic mate. Therefore, members of the fast sex must compete to mate with the slow sex.

This is where sexual selection comes in. The slow sex selects for good or attractive traits and mates with those in the fast sex that carry such traits. Sexual selection is the source for many sexually dimorphic traits between males and females. One popular example is the peacock's tail. A peacock has an iconic, but detrimental tail. The theory is that peahens favored bright and long tail feathers and eventually through runaway sexual selection the peacock's tail as we know it today was evolved. While the tail is certainly beautiful, it can land a peacock in a deal of trouble with predators making them easy to spot and catch. However, the catch is that while the individual is in danger, he is more likely to mate with a female because of the tail. It increases his Darwinian fitness while decreasing his individual survival.

The peacock's tail is also fitting for the "sexy-sons" hypothesis. In this hypothesis, it is thought that female selection results in male offspring with the attractive trait, and female offspring attracted to the trait. Thus the trait and it's attraction is preserved in successive generation guaranteeing the male offspring to have a good chance at mating.

Sexually dimorphic traits can be very costly to males, be it investing energy into developing the traits or the dangers that accompany them (ie. predators). However, despite the costs to the individual, it increases fitness which is what life is all about (in some opinions). This the core idea behind Richard Dawkins' book The Selfish Gene. Admittedly I have not finished the book but from my understanding it's about genes sometimes sacrificing the individual (through the means of altruism) in order to propagate themselves in the gene pool. Obviously I don't think Dawkins is suggesting that genes literally have hopes and dreams but rather that it is evolutionary adaptive for individuals of a species to cooperate (especially closely related individuals) to ensure survival of species (and genotypes). In a University of Portland commencement speech, Paul Hawken remarked, "We are here because the dream of every cell is to become two cells."

Wednesday, December 1, 2010

Chapter 14: Recapitulation and Conclusion

Well here we are at Darwin's closing statements, summarizing and reasserting the theory that he has so beautifully explained over the course of On the Origin of Species. When I started this project, it was an effort to save people from reading the book while still being able to understand its core tenants and science. However, it truly is a book that everyone (at least those with an interest in evolution and biology) should read. While some parts were daunting and drawn out, it really is a magnificently written scientific theory. Darwin spent a large portion of his life mulling over his observations, and perfecting them to the best of his ability. This is his life's work and legacy and it's really brilliant when you consider what was known and widely believed at the time.

If you are going to read nothing else, read chapter 14.

Darwin restates the concepts of variations withing species, and the struggle for existence. Darwin notes quite strongly that no matter how complex or perfect a trait or species may seem, it must have arisen through gradual modification. He also recovers geographical isolation, hybrids, sexual selection, geometric increases in population.

Darwin promotes the concept of use and disuse again. This theory is pseudo-Lamarckian and not really supported by evidence. In the absence of selective pressure, traits cannot appear or disappear. I suspect that Darwin considered use a selective pressure but the genetic basis of a trait and phenotypic expression would not be altered by use or disuse.

In closing, Darwin was confident that future research would support and expand his theory; his prediction was completely right. Today evolution is a main tenant of biological science and is fundamental in understanding life.

"There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved," (Darwin, 398).

Chapter 13: Mutual Affinities of Organic Beings: Morphology: Embryology: Rudimentary Organs

We're nearing on the homestretch with chapter 13, there's only one chapter after this one and it's basically a summary of Darwin's theory.

So here we go: Darwin begins by analyzing the shortcomings of the classification system, while it can show relationships, they are not very informative when it comes to inheritance and descent. Darwin was especially concerned with similarity in body plans and symmetry, as well as non-specialized traits and their impact on showing classification groups. He was also a proponent of discovering the genealogy of closely allied species and using that to classify them. However, in Darwin's time, it was difficult to discern genealogy without the knowledge and technology of DNA analysis.

Darwin explores the concept of convergent evolution, in which different species come to have the same adaptation but not from common ancestry but rather similar modifications. Darwin does not call it convergent evolution, but the concept of bats and birds having wings for the same use and not because they share a recent ancestor was recognized at the time by Lamarck's classification system. One example he gives that whales and fish have similar exteriors because they're adapted to the same surroundings but they themselves are not closely related.

On morphology, Darwin asserts that crucial parts such as limbs are reworked from an original template rather than completely thrown out and grown anew (ie: the fin of a whale is a modified leg from a former terrestrial ancestor). Darwin saw the analogous body plans of many different species as proof of common ancestry rather than a creator.

Darwin also talks about embryology and the similarity of early embryos of related species as well as how embryos are adapted just as well as adult forms for the conditions surrounding them. Darwin uses the example of a pigeon, shocker, to measure differences in juvenile and adult pigeons of different breeds to show their similarities at the juvenile stages. Darwin went off popular theory that embryos resemble ancient species. While they are simple and basically laid out I don't know that I agree with that exact assessment.

Darwin also covers vestigial traits, which he refers to as rudimentary organs and cites instances of underdevelopment in some individuals and fully functioning individuals. Vestigial organs are somewhat controversial today, because for some examples it is possible that the function is currently unknown. However, in most cases it is found that vestigial organs were useful in an ancestor and have now been replaced or rendered useless but are retained. 

And finally, I thought this quote was pretty funny out of context, "For the male is a mere sack, which lives fora  short time and is destitute of mouth, stomach, or other organ of importance, except for reproduction," (Darwin 369). He was referring to male larvae becoming "complemental males".

Tuesday, November 30, 2010

Chapters 11 and 12: Geographical Distribution and Geographical Distribution continued

Darwin spends two chapters on geographical distribution, rather than just making one forty page chapter on the subject. Without the knowledge of plate tectonics as mentioned in the last post, Darwin didn't really have a scientific context fro the similarities of species that he was seeing in distant lands other than they must have originated from a common ancestor and by one set of means or another managed to migrate to present locales. It was known based on the geological record that the sea level had changed over Earth's history, but the concept that the continents had undergone massive shifts wasn't widely accepted until the mid 20th century.

Darwin suspected that wide spread species began to divide in to variants specialized to a specific location and climate, thus branching into distinct species.  Therefore, all similarities between species could be accounted for by inheritance and similarities were products of selection. This fits with his theories and he strongly believed that all variants despite their present day location, had stemmed from a common ancestor. Placed into the context of modern understanding, this is possible, but at the time, Darwin faced a difficult task of explaining how such widespread migration across land and sea could have happened. However, despite this difficulty he reasoned that to reject the idea of migration and to accept separate acts of creation would be to accept miracles over his entire theory.

Darwin covers Charles Lyell's (the father of geology) concept of means of dispersal. This idea is that migration has been greatly affected by climate change which corresponds to sea level changes. According to this theory, continents and islands were once connected to each other by land bridges that are now covered by ocean. This is true of some land masses (Eurasia and North America were connected by a land bridge that allowed for human migration some 10,000 years ago) but this theory is limited to the idea that the continents don't move. Darwin question Lyell's assertion that all islands were once connected to mainland, and rightly so, since many have been formed by underwater volcanoes.

Darwin believed that plants were better at dispersing themselves than mammals, citing plants that are found around the world and that no continent shares a common mammal (at least one known at the time). Darwin even details his own personal experiments at seeing how well different seeds and other plant material handled sea-water travel to support the idea that seeds could float from the mainland to an island. Other means include seeds on floating driftwood birds transporting seeds by ingesting the fruits of plants, and then fly to islands to deposit them. Darwin even went so far as to investigating bird droppings on his property for evidence of seeds (hardy seeds were unsurprisingly better preserved than soft ones). Darwin also proposed transport via iceberg during glacial periods.

The concept of climate change is explored further while Darwin analyzes the impact of the ice age on different species in Europe and how it forced adaptation or migration south for many species. Darwin also alludes to the concept of the Bering Strait, "We can further understand the singular fact remarked on by several observers, that the productions of Europe and America during the later tertiary stages were most closely related to each other than they are at the present time; for during these warmer periods the northern parts of the Old and New Worlds will have been almost continuously united by land, serving as a bridge, since rendered impassable by cold, for the inter-migration of their inhabitants," (Darwin, 325). It's very striking that in the 1800's (and even earlier) modern concepts were already being predicted and hypothesized thus laying the ground work for modern science.

Above was chapter 11, detailing acts of creation against dispersal from a common source, with attention to plants. Chapter 12 concerns fresh water species and islands.

Specifically with fresh water fish, Darwin inferred that those isolated in Europe would not find their way to North America due to the distance. However, similar species within closer proximity could have been dispersed through changes in water level such as flooding. Again, Darwin repeats the idea of birds transporting plant matter.

For islands, which Darwin had an intimate working knowledge from his travels on the H.M.S Beagle, Darwin proposed that species found in such isolated areas stemmed from relatives on the mainland. Certain species are more able to get to far islands than others, for example birds and bats are able to travel a greater distance than terrestrial mammals.

Finally, Darwin speaks of his Galapagos studies. Namely, he discusses the variations observed on different islands, mentioning specifically birds and plants and that differences between them and mainland species have been generated through selection.

Thursday, November 18, 2010

Chapter 10: On the Geological Succession of Organic Beings

In this chapter, Darwin explores the known evidence for evolution in the fossil record. Through the fossil record, Darwin notes that the rate of change is not the same for every species, and that over long periods of time some forms seem not to change at all.

Darwin claims that land dwelling creatures seem to have changed more than those in the sea, citing that "higher" creatures change more than "low" creatures. That is to say that Darwin suspected that more complex creatures, due to their complexity and opportunities for variation are more likely to change due to environmental factors than more primitive creatures. This isn't necessarily due to Darwin's qualitative assessment of high and low creatures, but rather that highly complex creatures are often very specialized and would necessarily have to change in response to natural selection. The most basic and primitive bacterial extremophiles have not changed tremendously because they can live just about anywhere without too much selective survival.

One rule that Darwin states is that groups of species cannot simply reappear on the fossil record after a lapse of time. Explanations for this could be poor preservation or geographic migration in and out of a region. Basically once something is totally extinct, it's not going to magically reappear. In this chapter Darwin addresses the concept of extinction in detail. Darwin concluded from fossil evidence that most species gradually disappear over time as opposed to disappearing in large number due to catastrophes. While there have been several mass extinction events in earth's history, the appear to be more the exception than the norm. Most mass extinctions were not sudden, and instead drawn out over a long period of time. The Discovery Channel has an interactive website detailing mass extinctions and their likeliest causes.

Darwin predates the theory of plate tectonics by about a century, however in his time it was recognized that certain rock deposits and formations were located in different, seemingly unconnected areas and having similar fossil groups within them. Darwin saw this as parallelism, because it was probably he (and other geologists of the time) had no concept of the continents being in different positions throughout the ages. Instead of convergent evolution, it is more likely that similar forms do share a common ancestor and the population was geographically isolated from each other during continental drift, causing two new branches in the lineage.


Darwin also summarizes the idea of ancient forms being "lower" than modern forms. However, he notes that naturalists were still arguing the concept of what constituted high and low. Darwin simply decided to define it as modern forms were increasingly complex over their ancient forms.

Tuesday, November 2, 2010

Chapter 9: On the Imperfection of the Geological Record

Darwin dedicates this chapter as a sort of extension of chapter 6 (which discussed possible criticisms of his theory) specifically on the geological record. In context, the knowledge of the geological record in Darwin's time was not as large as it is today.

Darwin's main dilemma was that the fossil record was chock full of transitional forms. He knew that presently, it wouldn't be possible to identify transitional forms since it cannot be clear what they're transitioning into. He also recognized that similar existing species weren't transitioning into each other, but rather had a common ancestor that was different from both of them. "So with natural species, if we look to forms very distinct, for instance the horse and tapir, we have no reason to suppose that links ever existed directly intermediate between them, but between each and an unknown common parent," (Darwin, 270). The reason in which it is unlikely there would be intermediates between two living species is that both species would be subject to natural selection over the same time span and one would have to remain unchanged and the other would have had to undergone extensive change.

While it was understood in Darwin's time, largely due to Charles Lyell's research, that the Earth was much older than the Bishop Usher estimate of 6000 years. Yet it was nowhere near the modern accepted age of 4.5 billion years. Therefore, Darwin had understandable questions of whether the Earth was actually old enough to support his theory. The deepest strata uncovered in England was the Paleozoic strata.

A quick lesson on the geological time scale:
The Paleozoic era represents at it's deepest point 540 million years ago. Older than that is considered Precambrian (Stanford). In the last 50 years, the study of Precambrian age fossils has expanded and the oldest known life (microscopic single cell organisms) currently known comes from the Archean era (Schopf).

Fossilization is not an easy process, and many factors determine whether or not an individual is preserved. The specimen must be buried and petrified over time, however the remains may easily be destroyed or scattered by numerous processes (Stanford). The number of fossils known in Darwin's days were much smaller than what has presently been found. Darwin considered the paleontological record to be in a sorry state. Darwin correctly assumed that very few creatures are actually fossilized.

Another factor Darwin considered was the migration of animals to new areas and that an intermediate form may not be found near present day localities of species. He spends most of the chapter summarizing the known geological record and predicting why certain specimens (such as transitional forms) had not been found.

He also muses that even if a transitional form was found, it may not be recognized as such and variations can be categorized as separate species, leading to redundancy and confusion concerning relationships. This is still a concern today, with certain fossils being mislabeled, or one species given several names.

Darwin's main concern was the sudden appearance of complex fossils in the geological record, because for his theory to work, there would have to be more primitive forms before them. At the time, no fossils older than the Silurian stratum had been found, but as I mentioned earlier, Precambrian fossils have been discovered.



Monday, November 1, 2010

Evolution and the Media

I prefer to get most of my news online rather than from the TV these days, and one thing that I've noticed over the past 2 years since starting to study human evolution is that the media tends to skew evolution stories towards a sensational angle. Every fossil primate is toted as a possible human ancestor. Most recently I've found multiple stories about the same set of fossils found in Libya that indicate that primates likely originated in Asia, not Africa. Apparently this is raising a lot of controversy (although, in a class I had last year, Asia as the cradle of primate origin was taught as the accepted view of the paleoanthropology community). These fossils are almost 40 million years old, and while they're certainly human relatives, to call them important discoveries for the field of human evolution is kind of off base.

Yes, plesiadapiforms and other early primates are part of human evolution and I don't want to diminish the importance of such finds, but the media shouldn't be calling them early humans. Humans and chimpanzees didn't even split until 7 million years ago, so to call anything older than that even remotely human is misleading. The news media also tends to group all hominid fossils as humans. This may be personal bias, but I don't consider Homo erectus human, and I certainly don't consider any of the Australopithecus humans, at least not in the sense that the news media is making them out to be.

I realize that my concept of what is human is kind of limited (specifically to anatomically modern humans) but at least I have a clear definition. When the "Ida" fossil was publicized in 2009 a few news sources hailed it as a missing link in human evolution. Yeah, I guess it's part of human evolution but it's more relevant to early primate evolution and the link between lemurs and monkeys. It's very misleading to present anything that far back on the evolutionary timeline as human. That would be akin to me saying that I'm President Obama's cousin, I mean very distantly it's possible that many many many many generations ago we had a common ancestor but it's not like we're celebrating Thanksgiving together.


The purpose of the news is not to inform but rather to make money. Placing a headline that read something about human ancestors is much more likely to be read than a title about what the article is actually about. Ancient monkeys don't sell as well as ancient "humans". Humans are pretty species-centric, and at least the media is getting people to read about evolution (even though they have to trick them into it). Face it, writing about Ida as a lemur-monkey link is far less entertaining and attention grabbing than hailing it as a crucial find for human evolution.

As a whole, it seems most people just don't care about fossils (unless they're mega fauna) or most science in general. The media can help to make certain fields seem sexier, and controversial, but it can also hurt science by misrepresenting it to the public. It's even more damaging when certain theories aren't implemented into the science curriculum of K-12 schools because it may offend people. Science is impartial. Finding facts offensive doesn't negate their truth. This leads to some people only being exposed to specific ideas through these distorted media outlets. This whole system propagates misinformation.

Another saddening news media trend is that science sections are grouped in with technology. Therefore, most of the stories are about the latest Apple product and newest video games rather than actual science. Or, if they're not lumped together, the science section is hidden near the bottom of the page. Most print newspapers only have a science section once a week. Even the Discovery network is dominated by shows about people with 10+ kids, cupcakes, occupational hazards, and other not exactly scientific shows. As painful as it is to face, here in the 21st century science is getting the shaft.

Here are links to two stories about the ancient primates found in Libya. Very interesting, but not in the context of what makes us human.
NYTimes: New Anthropoid Species Uncovered in Libya
The Daily Mail: Human evolution started in Asia? Ancient ancestor walked Sahara 39m years ago.

Saturday, October 30, 2010

Chapter 8: Hybridization

In this chapter Darwin tackles the issue of reduced hybrid viability, believing that sterility was a by-product of the varied characteristics gained from two different species. To do so he mainly focuses on experiments done on plants and animals and the varied degrees of fertility of hybrids.

In a previous post I discussed wild hybridization and the ability of hybrids to survive in conditions that neither of their parent species thrive in. Many of Darwin's examples are of the intercrossing of closely related species, such as variety of cattle and geese. Darwin believed that the sterility of hybrids was caused by the incompatible crosses of reproductive organs. Today we know that sterility can arise through an incompatible number of chromosomes, a prominent example being mules. Horses and donkeys have different numbers of chromosomes and so the resulting Mule has an unpaired chromosome which leads to difficulty creating a viable embryo.

Darwin made a distinction between hybrids of distinct species and what he called "mongrels" or the offspring of distinct varieties of the same species. This difference leads to a powerful closing statement: "There is no fundamental distinction between species and varieties," (Darwin, 268) based on the observation that mongrels often have increased fertility.

The chapter is difficult to summarize without taking into account modern knowledge of hybridization. Darwin had no direct knowledge of pre and post zygotic barriers, but he did guess at the fact that some reproductive systems in hybrids were non-viable because the parent species were too incompatible.

Chapter 7: Instinct

Despite writing a whole chapter about instinct, Darwin states this right away, "I will not attempt any definition of instinct," (Darwin, 225) because apparently everyone understands what instinct is. If you're unsure, for purposes of this chapter it is inherent knowledge that does not need to be taught (eg, the location of ancestral breeding grounds, how to make a nest, etc).

Darwin muses on the similarities of instinct and habit for a bit, wondering if habits eventually become instinct. This to me seems slightly like the modern concept of the meme, but memes in my opinion cannot be instinctual. Darwin applied the concept of gradual change to the acquisition of instinct as well, and that complex changes don't spring up over one generation.

Darwin also brings up the idea of extra-species altruism, though he doesn't explicitly call it that. "The instinct of each species is good for itself, but has never...been produced for the exclusive good of others," (Darwin 227). Species do benefit other species but it is usually for some sort of gain, whether or not that gain is visible or understood. This again relates back to the theme that there is a great deal of interconnected dependence between different species, which has been repeated throughout Origin.

Instinct hasn't been cracked yet (a brief google search reveals more movies and phones than scholarly discussion) and the nature vs. nurture debate still rages strong. Therefore, Darwin's assertion that instinct is selected for probably isn't off the mark. Many things have a biological basis, even if it's not immediately clear. If animals are born "knowing" something, the simplest explanation is that it's biological. If it is solely biological then selection most certainly applies.  Sociobiology seeks to study the link between genes and behavioral traits.

Darwin gives three examples of natural instinct: cuckoos laying their eggs in other nests to pass off parental investment onto another bird, ants' "slave-making", and bees making honey combs. I get the cuckoo thing, and the bees, but the ants section doesn't really make much sense to me. Admittedly I know nothing about ants apart from what I've seen in A Bugs Life...so really, I know nothing. Apparently Formica sanguinea, a type of ant, takes slaves (other species of ants). Even Darwin seemed skeptical of this ant species (to the point of putting a few colonies in his yard to observe), but apparently they take over other species nests rather than building their own (Sonobe, R. Onoyama, K http://ant.edb.miyakyo-u.ac.jp/E/Taxo/F80701.html).

Thursday, October 14, 2010

Chapter 6: Difficulties on Theory

Here Darwin addresses concerns/confusion concerning his theory of natural selection. In this chapter, Darwin addresses a lack of transitional forms and the so called perfectness of specific structures.

Transitional forms: Darwin recognizes that transitional forms are replaced by successive generations of forms, but questions why there is a lack of fossil evidence (1). There were known fossils in Darwin's time, but not to the extent that there are today. Fossilization is a rare process, and most individuals are destroyed. For instance, there is very little information on chimp evolution due to the fact that so few fossils from that lineage have preserved.

For instance Archaeoptreryx lithographica, an early feathered dinosaur, was not discovered till 1861. Since then, only 7 specimens have been found (2). However, obviously for the species to exist, there had to be much more than 7 individuals.

To address the question of why we don't see transitioning forms today, it's because we don't know what they're transitioning into. Evolution is a very long, slow process.

Darwin inferred from the geological record that Earth in modern times is experiencing a more stable array of climates (of course this is pre-global warming concerns). Therefore, in times of great climate shifts and unstable environments, life may have had to adapt more extremely. Darwin asserts that "continuous conditions" are mainly responsible for the diversity of species populating the world. This means that life is not restricted to one zone, but differs in distribution for select climates (1).

However, it's not just about climate, it's about other species too. The predators, the prey, the whole circle of life bit. Speaking of which, The Lion King (the first movie I ever saw in theaters!) demonstrates a lot of Darwin's ideas. Work with me here, the hyenas move into the lions territory and eat up all the food subjecting the lions to the choice of either finding a new territory or starving to death. Of course in the movie there is option 3, kicking the hyenas out of pride rock in a symbol heavy disney ending, but that's adaption! As a side note, the lioness' fitness was really suffering through that movie. There were only two cubs and then no males for a very long time.

Okay, enough pop culture, back to the book. Darwin brings up the genus Balanus, and that individuals appear as intermediates between the main varieties (1). What exactly is the genus Balanus? Well, it's a type of barnacle. Darwin was a bit of an expert on barnacles so I'm going to trust him on this. He has a multi-volume book about barnacles (he might love them just as much as pigeons, though I don't think that a barnacle can express as much response as a pigeon -- I imagine them to be along the lines of pet rocks, but perhaps less exciting) which I will not be reading. 

Darwin also addresses species that are highly adapted to specific behaviors. His choice example is the bat evolving from a flying squirrel, and a whale evolving from a bear (1). These are very theoretical and very wrong; while bat evolution isn't well documented, whale evolution is and they evolved from large land carnivores (that weren't bears).

Next, Darwin covers so called perfect structures, namely, the eye. We now can trace the mosaic evolution of the eye, but such advances weren't available to Darwin who seems baffled by the perfection. However, he was very certain that all features in species can be explained by gradual change. One argument he uses is that certain organs or features may end up being used, and adapted, for a completely different use than how they were originally selected for (1).

Darwin goes on to discuss vestigial organs (without directly calling them that). He muses that they are leftovers that were useful to an ancestral form, which is true. His other concern is of traits that are assigned importance, but are just by-products of selection. Also, Darwin finally brings up humans, specifically races but doesn't have any explanations for them (1). Which is probably for the best.


Thursday, October 7, 2010

Chapter 5 - Laws of Variation

In this chapter Darwin outlines his views on variation and its causes. Darwin published On the Origin of Species in 1860, in a time when genetic inheritance wasn't well understood. Previously I have mentioned Mendel, however his work did not gain recognition until 1900. One argument constantly made against Darwin is that because he got some details wrong, his whole theory is wrong. Science is a process, old ideas are replaced with new ideas, incorrect information gets corrected. So Darwin didn't understand genetic inheritance, big deal, he was at least able to recognize the fine details of change over time and selection. Sure, evolution is just a theory, but so is gravity. Scientific theories are shown to be true time and time again, can be replicated, and are observed all over. It's not an abstract concept someone just came up with to explain something, it's a repeatedly observed phenomenon. I cannot understand how some people can selectively pick and choose what science they want to believe in. If you don't believe in evolution, what's the point of getting a flu shot every year? A new flu shot attempts to protect patients from the ever evolving strains of flu.

Okay, I'll get off the soap box and onto the chapter. Variation has been a big theme in Origin thus far, so it's fitting that it gets a chapter. Darwin believed that most variation occurred in the womb. Yes, while developmental interruptions or stresses can result in a deformed offspring, these variations are not genetic and thus not heritable. Darwin admits that there is large ignorance concerning the subject. However, Darwin also says that most variation cannot be accounted for by climate and food.

"When a variation is of the slightest use to a being, we cannot tell how much of it to attribute to the accumulative action of natural selection, and how much to the conditions of life," (Darwin, 179). Please Darwin, be more cryptic. This chapter is confusing, and I think part of that is derived from the fact that modern audiences have the benefit of 150 years of the study of evolution. Some of this stuff is just plain wrong and or confusing.

Darwin spends time talking about use and disuse. I could bore you with the details, but it's not how variation arises. Here's the hypothesis: the use of certain traits makes them more prominent and the disuse of other traits causes them to diminish over generations. Observation wise this kind of makes sense, however natural selection acts to select traits that increase reproductive success, not just survival traits. Also, the use of a trait during an individuals lifetime would not make it more prominent in it's offspring. Instead, directional selection can explain the emphasis on certain traits over time.

Darwin recognized that certain structures in the body lead to change in others. Of course, the body must work together in a complementary way to ensure the greatest chances of survival.

There is a section on the variability of secondary sex characteristics (traits associated with sex that are not directly involved in reproduction) and their similarities in placement between closely related species. This idea could be elaborated into the fact that basic body plans are observed throughout nature, but Darwin doesn't take things so far.

Then of course there's a rant about pigeons -- because what would the Origin be without a tangent or two about Darwin's favorite bird? Yes, he knew a lot about breeding them and they did aid in his observations but really, enough with the pigeons! He's essentially hitting on recessive traits appearing, but does not call it this. He believed that the traits get diluted (and uses some questionable math to boot) over generations and believed that both parents needed to have some of this diluted trait for it to appear in offspring. Yes, and no. There are several ways that traits can appear in progeny, I explained recessive traits in my genetics post, and there are also epistatic genes. Anyway, it's not that the trait gets diluted, it just doesn't get expressed because of the other genes dominating it. Genes aren't cumulative. Darwin considered the appearance of such traits to be a throw back to an ancestral trait.


"To admit [to believing in independent creations of species] is, as it seems to me, to reject a real for an unreal, or at least for an unknown, cause. It makes the works of God a mere mocker and deception; I would almost as soon believe with the old and ignorant cosmogonist, that fossil shells had never lived, but had been created in stone so as to mock the shells now living on the sea-shore," (Darwin, 200). Religion is not a subject I choose to tread here on the internet. People are entitled to their beliefs and lack there of as they please. This blog is about Darwin, and I am inferring from the above passage that he may have been able to reconcile the idea of a god with evolution. I personally have not read anything written by him stating his religion. It is, frankly, irrelevant. Religion should not impede scientific observation and theory. Science should not be compromised to religious belief and it is up to scientists to keep their work and spirituality in separate spheres to ensure the greatest quality of research. And that's all I'm going to say about that.

This chapter overall presented several false ideas. Darwin knew there was variation allowing for natural selection, however he had no clue what caused variation. This makes for some confusing reading since he tries to explain variation but then states that his ideas are probably not the main cause of variation.

Saturday, October 2, 2010

Chapter 4: Natural Selection

Finally, we get to natural selection, the big show, the process by which Darwin saw evolution.

"This preservation of favorable variations and the rejection of injurious variations, I call Natural Selection," (Darwin, 144). Well put Darwin. Natural selection can be basically boiled down to the simple concept of traits that allow an individual to survive the best will be passed onto the next generation.

Darwin explains that if there is a sudden change in environment, it's inhabitants must adapt or perish. Also important is the fact that different species have an impact on each other, whether it is a predator/prey relationship or a competition for space or food. This complex relationship seems to have fascinated Darwin as he has mentioned it in previous chapters. "Let it be remembered how powerful the influence of a single introduced tree or mammal has been shown to be," (Darwin, 145). A modern example of this can be seen in invasive species that come to an area and disrupt the local ecology.

Darwin believed that direct changes in climates affected variability, "A change in the conditions of life, by specially acting on the reproductive system, causes or increases variability," (Darwin 145). It is difficult to access the role that the environment plays in variability. Variations are rooted in genetics, but Darwin obviously had no understanding of modern genetics. So yes, while the expression of some genes is determined by factors such as temperature, this is not the case for all genes. Therefore, the directed change of natural selection is acting on existing individuals survival, and not the variations of developing individuals.

"Every selected character is fully exercised by [nature]; and the being is placed under the well-suited conditions of life," (Darwin 146). Darwin cited the example of birds and insects being the same color as their habitat as an example of natural selection. This makes sense: if a bug lives on red leaves, variations of the bug that are red are camouflaged better than variations of another color. Since the other colors would be easier to spot, they would be eaten more and the red ones would be left with more food and access to mates.


Darwin also points out that variations that occur during specific life stages are repeated in offspring. For instance, if a goat is going to grow horns, it will do so at around the same age that it's parents first grew horns. Unknown to Darwin, such developmental features are determined genetically.

Sexual Selection is mentioned in this edition as a process through which selection is determined by mate choice. This is mostly observed in males, as Darwin notes, because they are most often the sex competing for mates. Sexual selection rightly deserves it's own blog post so look for that soon. This sort of selection creates divergence between the sexes (sexual dimorphism) and focuses mostly on contest-competition and displays. Darwin notes examples of deer and birds.

Darwin gives many examples of natural selection in this chapter with animals and plants. However, the evidence he uses is mostly circumstantial and not derived from direct observation. Yet, because evolution is such a long process it is not surprising he could not directly observe many of his theories in action (although he did take 30+ years to publish his ideas, think of how many generations of fruit flies he could have gone through!). As a side note, there was a very interesting study of Galapagos finches, which were regarded as highly inspirational for Darwin, and the effect of climate change on their beaks over many years.

Moving on, Darwin talks briefly about intercrossing (hybridization gets it's own chapter, look forward to that). He also has a tangent about hermaphrodites and their reproductive prospects. Incorrectly, Darwin assumes that no animal species reproduces asexually. Wrong. While sexual reproduction is the norm, there are examples of asexual species and those that can reproduce through parthenogenesis (when an egg develops without fertilization; this has been observed in some fish, reptiles, and insects). I'll let Darwin pass on this one, I don't think he ever encountered any such species in his travels and if he did I doubt he lifted up the legs on each lizard to check it's sex (they'd all be girls)... Basically, what Darwin is saying is that even if a plant or animal can reproduce itself, pairing of animals is essential to create variation and increase diversity.

Darwin explains how different factors impact natural selection, such as isolation and large areas. Darwin's view was that natural selection seeks to fill every niche. Also the layout of the land, and whether or not it is isolated impact natural selection. If no new species are moving into an area, the native species are not challenged and not subject to strong selection due to a change in predators, space or food sources. Darwin favored the idea of species doing better over large areas that they could spread out and populate. Confined, isolated areas stagnate change and create what Darwin referred to as living fossils -- species that have not changed very much over thousands of years because they are so well adapted to their isolated spot and nothing has invaded to force for selection.

Extinction is the next topic Darwin tackles, basically summing it up as varieties that do not do as well become rarer and if they are not selected for over a long enough time, they go extinct. Brilliant insight Darwin. "Consequently, each new variety or species, during the progress of its formation, will generally press hardest on its nearest kindred, and tend to exterminate them," (Darwin 163). Therefore, Darwin believed that extinctions were caused not by extremely different species (with presumable different needs) but rather similar ones competing for the same resources.

The idea of extinction is followed by the important concept of divergence of character. This idea is that as variations become more pronounced, they move towards a category of sub-species, and then fully differentiated species. Darwin never really defines what a species is, which again for purposes of these posts, I am defining as groups that do not/cannot mate with each other and thus do not exchange any genetic material that result in viable offspring. Since Darwin viewed selection as trying to optimize the use of the environment, divergence would allow for the maximization of species in different environments. "As a general rule, the more diversified in structure the descendants from any one species can be rendered, the more places they will be enabled to seize on, and the more their progeny will increase," (Darwin, 170). In this section, Darwin draws an imagined phylogeny tracing many different species back to a common origin. This is one of the most important concepts to be hammered home: species are descendant from common ancestors. The more species diverge, the less related they are to each other.

The importance of this chapter is insurmountable. Darwin ends the chapter quite poetically, "As buds give rise by growth to fresh buds, and these, if vigorous, branch out and overtop on all sides many a feebler branch, so by generation I believe it has been with the great Tree of Life, which fills with its dead and broken branches the crust of the earth, and covers the surface with its ever branching and beautiful ramifications," (Darwin, 177).

Sunday, September 26, 2010

Natural Selection in the News

An article in the NYTimes last week talks about research with fruit flies that supports the idea of multiple gene frequencies changes over generations leading to change (evolution) and not the idea of big infrequent mutations leading to change. The article termed this "soft sweep" and it makes sense given mutation rates and the chances that a mutation is positive rather than neutral or detrimental to an organism. This is not to say that mutations don't give rise to change (they do), but rather that they do not seem to be the norm.

This research also supports the concept of many genes controlling traits, as opposed to just a single gene for each trait. This is becoming a focal point of disease research. While some diseases may be controlled by a single gene, some diseases are likely subject to control by a whole slew of seemingly unrelated genes. This is why certain disorders may run in families, but have no discernible genetic basis. It makes it very difficult then to access how at risk someone is for a certain disorder, and since environmental factors definitely play a role in gene expression, it could be extremely hard to predict an individuals likelihood for a specific disease.

Friday, September 24, 2010

Chapter 3: Struggle for Existence

Darwin pretty much sums up natural selection in the beginning of the third chapter, "Owing to this struggle for life, any variation, however slight and from whatever cause proceeding, if it be in any degree profitable to an individual of any species, in its infinitely complex relations to other organic beings to external nature, will tend to the preservation of that individual, and will generally be inherited by its offspring. The offspring, also, will thus have a better chance of surviving, for, of the many individuals of any species which are periodically born, but a small number can survive," (Darwin, 132).

Darwin preferred the view of competition between individuals over cooperation in groups as the main drive of evolution, a debate that is still strong today -- how much of a species survival is determined by individual success against group success? Social Darwinism is all about competition, and not really at all about biology at all. However, it is an important distinction to make. Survival of the fittest is Social Darwinism, actual Darwinism is more along the lines of the fittest having the greatest reproductive success. Social Darwinism came about around the time of Darwin's publication, and was quite influential in an already competitive Victorian society. Darwin himself didn't actually espouse the ideas, they were actually started by Herbert Spenser. Social Darwinism was used as a justification for imperialism, exploitation, unchecked capitalism, eugenics, and a slew of other evils (2). The point of this little tangent is that Social Darwinism does not equal Darwinism, at all. I can't tell you how many times I've seen this mistake propagated by the media, specifically network news.

Back to the book, chapter 3 is also kind of short and is all about natural struggle as well as geometric increases in population.

Geometric increase is basically exponential increase, meaning that the population will increase steadily exponentially rather than at a steady linear rate. This accounts for rapid increases in populations. Darwin used the example of elephants, because they live a long time and produce a very small number of progeny. His math leaves a lot to be desired, but he was right in a very basic sense. So Darwin proposed that an elephant lives about 90 years and has 3 calves, and each of those calves grow up to have 3 more. Darwin estimated that after 500 years, there would be something on the order of 15 million elephants stemming from one pair (1). Well, no, actually if we're talking approximately 5 generations, that would be 3^5 elephants, or 243. This is opposed to linear growth in which 5 generations would yield 3x5 or 15 elephants, big difference. Did no one think to check these calculations before publishing; I mean, if Darwin had been right, we'd be up to the empire state building in elephants. Also, not every one of those 3 calves are going to necessarily have three calves because some of them are going to have to be male (or else there will be no elephants). Regardless, geometric growth is how species propagate.

Speaking of those elephants, not all 3 calves will survive to produce calves of their own, thus the struggle for existence. "Hence, as more individuals are produced than can possibly survive, there must in every case be a struggle for existence, either one individual with another of the same species or with the individuals of distinct species, or with the physical conditions of life," (Darwin, 134). Basically, more progeny must be produced because not all of them are going to make it. This also brings up differences in parental investment, species that invest a great deal in their offspring generally have fewer than those who do not beyond birth, but I'll save that for a separate blog post.

Darwin brings up the effect of climate on the struggle for existence, and how particular occurrences such as cold winters or dry summers impact populations short term. Later in the chapter Darwin suggests that certain varieties could mix to produce an individual better suited to a certain environment, and varieties ill-suited to the climate will soon disappear (1). This is basically a primer for natural selection, which is detailed in the next chapter.

He also notes the impact of one species on another. Darwin recognized the relationships between species, and used an example of certain bees associated with specific flowers. Darwin extends this to the bees being impacted by field mice, which are impacted by cats. Therefore, one could muse that a decrease in cats would lead to a decrease in flowers (since the mice would increase and damage the bees in greater number) (1). This co-evolution is widely seen today, and even in ourselves. E. coli is one such example; it has evolved to live in our guts and we depend on it to aid in our digestion.

Darwin leaves us with this small comfort, "When we reflect on this struggle, we may console ourselves with the full belief, that the war of nature is not incessant, that no fear is felt, that death is generally prompt, and that the vigorous, the healthy, and the happy survive and multiply," (Darwin, 143). Doesn't that just leave you feeling warm and fuzzy?


Wednesday, September 22, 2010

Phylogenies

In my search for a modern and illustrative phylogeny, I found this cool poster

I was really hoping to find a phylogeny I had seen in an article last year that showed a really wide array of organisms classified based on their degree of genetic relatedness, however I couldn't find one that fit such a description from a reliable source.


Chapter Two: Variation Under Nature

Darwin begins to define a species by pointing out that each individual of a species has in it, some form of variation. Darwin also goes on to point out that it's more likely that there is one species with, for instance, 3 varieties, rather than 4 distinct species.

This assumption that there are many varieties rather than many distinct species is correct. It is difficult to define what exactly a species is. A generally taught view is that speciation occurs when varieties of a species cannot contribute genetic information to each other, or in other words, two varieties that cannot breed. A few posts back I posted an article that talked about distinct species breeding. One example of this are lions and tigers (two genetically different big cats from different geographical locations, and pretty much universally accepted as separate species) producing "ligers". One note to make is that many hybrid offspring are non-viable, meaning that they are either weak and/or sterile. Liger's don't really count as tigers contributing to the lion gene pool because they cannot be bred.

For purposes of this blog, I'm defining different species as groups of individuals who do not contribute to each others gene pools. Such reproductive isolation can be mechanical, or geographical, and/or pre/post zygotic non-viability.

"And I look at varieties which are in any degree more distinct and permanent, as steps leading to more strongly marked and more permanent varieties; and at these latter, as leading to sub-species, and to species," (Darwin, 126). Darwin defines a species as a variety that is able to flourish in large numbers, and does not assign the rank of species or even sub-species to each and every variant.

"Where many species of a genus have been formed through variation, circumstances have been favorable for variation; and hence we might expect that the circumstances would generally be still favorable to variation. On the other hand, if we look at each species as a special act of creation, there is no apparent reason why more varieties should occur in a group having many species, than in one having few," (Darwin, 129). Basically the processes shaping variation long ago are still shaping variation today, and if creationism was applied to each and every species, there would be no explanation for variation.

It is important to note that the Linnaeus system of classification was widely known during Darwin's time and is still used today. This is a system of classifying organisms based on their relatedness. One major advancement to this system is the use of genetic analysis to see just how closely species are related.

One other observation Darwin made in this chapter was that the dominant genera represented in a region was also apt to have the most variety.

Thankfully, chapter 2 of Origin is much shorter than chapter 1 and pigeon free.

Thursday, September 16, 2010

A brief detour: Genetics

Before I begin detailing Chapter 2 of Origin, I would like to take a brief look at our modern understanding of genetic inheritance. This serves two purposes, a basic grasp of Mendelian principles helps one to understand evolution in light of genetic inheritance, and also I have a genetics exam tomorrow morning (lucky me). The textbook I use for my class is Genetic Essentials: Concepts and Connections by B. A. Pierce, published by Freeman, 2010.

Gregor Mendel (1822-1884) was a little known contemporary of Charles Darwin. His research gained popularity years after his death, and was rediscovered in 1900. Mendel's now famous experiments were done on pea plants. He would take true breeding (homozygous) pea plants that express two different traits (denoted as the P generation) and cross them. The offspring (the F1 generation) would then be genetically heterozygous for whatever trait Mendel was isolating, but would only express the dominant phenotype. The subsequent generation (the F2 generation) derived from crossing the F1 generation would result in a phenotypic ratio of 3:1, meaning 3 plants would express the dominant phenotype to every 1 plant expressing the recessive phenotype.

Hope I haven't lost anyone. These are somewhat confusing terms if you haven't had a biology class in a while.

We receive one set of genetic information from our mother and one from our father. I find the easiest example of this to be sex. Sex is determined by what chromosomes we receive, XX being female, and XY being male. A mother always passes one of her X chromosomes to her offspring. A male will pass on either an X chromosome or a Y chromosome to his offspring. So we can use a Punnet Square to determine the different outcomes for what the offspring may turn out like:

Please excuse the crudeness of my MS paint punnet square. I'm also sure my professor for Sociology of Gender would just love that I used pink for females and blue for males. Anyway, as you can see, the sex ratio is 1:1 for sex.

Mendel was looking at alleles (different forms of the same gene). He focused on the phenotypic (physical) traits of parents and offspring and crossing them to see what happened.

So, the P generation would be YY (heterozygous dominant) and yy (homozygous recessive) for traits. Let's say that YY is yellow and yy is green. The F1 generation would all be Yy (heterozygous) and would all express a yellow color. The F2 generation would be YY, Yy, and yy at a ratio of 1:2:1, with YY and Yy expressing yellow while yy would express green. Mendel found this 3:1 physical expression ratio to hold true across his many experiments. It works as a basic model for predicting the inheritance of unlinked traits.

Punnet squares can also be applied to alleles that don't have complete dominance. An instance of incomplete dominance is when the phenotype of the heterozygous offspring is an intermediate between the two parents (ie a pea plant that is some color between green and yellow); co-dominance is when both phenotypes are expressed (ie a pea plant that is both distinctly yellow and green). In these cases, the F2 generation would have a phenotypic ratio of 1:2:1 (totally yellow, mix, totally green).

Mendel shows that traits that are not expressed can still be carried by heterozygous individuals and may be expressed in the next generation when two carriers reproduce. This ties in with Darwin's instances of animals reverting back to their "aboriginal states".

So how does this play into evolution? Sexual reproduction creates a huge amount of variation. Variation is necessary for natural selection to favor some individuals over others allowing for greater reproductive success and the propagation of the alleles that produce such traits.

Chapter 1: Variation under Domestication

Darwin begins On the Origin of Species with a familiar example, that of domesticated plants and animals, to illustrate the concept of variety. Darwin asserts that variety is product of sexual reproduction, which is correct, and also mentions experiments that suggest that development during the embryonic stages can impact the individual later on (these experiments specifically concentrated on deformities resulting from embryonic trauma). Arguably, this is an early example of nature vs. nurture; Darwin's focus rests on the nature side of this argument. (1)

With domesticated organisms, humans guide the selection process. However, Darwin also points out the sterility of many domesticated plants and animals, as well as their "weak and sickly" nature. He notes that animals taken from the wild have difficulties breeding in captivity, but that animals that have been domesticated breed under quite "unnatural" conditions, such as rabbits in a hutch. (1)

Worldwide domestication of plants and animals began approximately 10,000 to 7,000 years ago, kicking off the first agricultural revolution (2). This allowed for the creation of permanent settlements and stratified societies as well as a population boom (2). Animals that were have been domesticated over thousands of years are dependent on humans for survival, just as humans are equally dependent of them for food (2). The fact that they have been adapted for domestication  means that they will thrive and reproduce under human constraints, whereas animals adapted to the wild have difficulties living and breeding in captivity.

Darwin suggests that traits correspond to use, such as bigger udders in species of cows subject to heavy milking, light wing bones in domesticated fowl that do not need to or are prevented from flying, and drooping ears in livestock that fear no natural predators. (1)

Darwin breaks varieties of similar animals into races. That is to say that there are several races of cows rather than species (1). This terminology leaves a lot to be desired, I prefer to call distinct variants of the same species breeds. To quote Darwin, "I do not believe, as we shall presently see, that all our dogs have descended from any one wild species; but, in the case of some other domestic races, there is presumptive, or even strong, evidence in favor of this view." (pg. 105).

Well, Darwin was wrong about different dogs being from different origins. Dogs have been traced back to the domestication of wolves in the middle east approximately 15,000 years ago. All the variation seen in modern dog breeds is a result of human selection for certain traits (3). However, Darwin was right to think that different domestic breeds were from a common ancestor.

Darwin also cites examples of animals that always have traits that go together as an example of the "mystery" of variation. Darwin had no working knowledge of genes as we do today. However, he was able to recognize some of the basic ideas of inheritance and considered it the rule rather than the exception.

Darwin goes on to talk about pigeons for at least a few pages. Darwin seemed to be quite the pigeon enthusiast and breeder. One thing he did stumble upon was the basic laws of Mendelian inheritance and the reappearance of recessive traits in the F2 generation (that is to say, for those unfamiliar with genetic inheritance patterns, that a recessive trait bred against a dominant trait will not appear in the offspring of that cross, the F1 generation, instead it will appear in the offspring of the F1 generation). Darwin did not do as extensive experiments as Mendel, and historical opinion holds that he was not familiar with Mendel at all. Darwin considered the reappearance of recessive traits to be the individual reverting towards its ancestral form (1). I don't know that this is exactly the clearest explanation; for a while, the importance of gene inheritance and long term evolution was not the focus of science.

If you are reading along with me in Origin, be prepared for just pages upon pages of pigeons. This might be why the book is so unread. Darwin should have written a follow up volume called On the Origin of Pigeons. It might have been longer. 

Once the pigeon saga is wrapped up, Darwin dives into the concept of artificial selection (when humans guide the breeding process of plants and animals to produce specific traits). Artificial selection is historically recorded and is the process through which wild plants and animals are domesticated (1).

Darwin eases his audience into accepting natural selection by giving first the familiar example of artificial selection. If man can do it, why not nature?


Wednesday, September 15, 2010

What's in a species?

Species are often defined as genetically distinct groups that cannot interbreed, but this line is often blurred. Take for instance an article in the NYT from Monday that explores hybridization. While most hybrids do turn out sterile, is it possible that these animal mash-ups are better suited for intermediate environments than their parents? When put into the context of global climate change, are these hybrids a response to environmental pressures?

Well, I don't think necessarily that natural selection is guiding towards cross species mating because most offspring are not viable; the occurrence of these hybrids in the wild is interesting none the less. The evolutionary context is that viable hybrid offspring could be responsible for some modern day species, perhaps even our own. And that is exciting.

Friday, September 10, 2010

Let the Voyage Begin!

It's been almost 151 years since the publication of On the Origin of Species by Charles Darwin. Yet, how many people today can claim that they've actually read this monumentally important work?

I am in the process of reading Origin and, even as someone who studies the processes of evolution every day in class, this is a difficult book to get through. Also, Darwin wasn't exactly right on everything he presented. He didn't have access to the knowledge that we in the 21st century have, such as genetic analysis. However, he still provided great insight into the process of gradual change and introduced evolution into mainstream scientific thought.

So here's the deal: One book, one semester. Each week I hope to post an exploration of a chapter of On the Origin of Species. The edition I am using is the 2nd edition, edited by Joseph Carrol and published by Broadview Texts in 2003. There are 14 chapters, and because this is a project for a class, I have a deadline of 12 weeks.

I have no idea where this project will take me. I hope to give a summary of each chapter, point out what's right, point out what's wrong, and give examples of Darwin's concepts illustrated by modern science. So, for better or worse, let the voyage set sail.