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).