Evolution: Darwin’s Dangerous Idea (2001) is a documentary co-written and co-directed by David Espar and Susan K. Lewis about naturalist Charles Robert Darwin and his theory of evolution, published in 1859, that established that all forms of life on Earth are related because they descended from a common ancestor via natural selection, a process whereby individuals better suited to their environment survive and reproduce while those that aren’t well suited perish, thus creating genetic changes in populations which overtime can become so great that a split from the original population occurs, leading to the formation of new species.
Biological evolution (genetic change over time in populations via descent with modification through genetic inheritance) is caused by four mechanisms: natural selection (individuals better adapted to their environment tend to survive and reproduce, thus passing their genes to their offspring), mutation (a change in the structure of a gene), migration (gene flow from one population to another) and genetic drift (a change in the frequency of a gene in a population due to random chance).
David Page: “In the 19th century, in Darwin’s time, it was audacious to claim that humans and chimps were closely related. There wasn’t that much scientific evidence. But since that time, the evidence has become strong. First, we saw the fossil record appear. Evidence of human ancestors that had apelike features established the plausibility of the idea that humans and chimps had common ancestors. And then in the last twenty years, we’ve seen the emergence of a whole new type of data that’s established a close relationship between chimps and humans. And that comes from the analysis of DNA. This is DNA. We’ve got DNA. Chimps have got DNA. Bacteria have got DNA. Petunias have got DNA. Crabs have got DNA. Every living animal, plant, fish, frog has got DNA, and if we compare the DNAs of any two species, we can establish how closely related they are one to another. [...] Here we’re looking at the DNA sequences of one particular gene that’s found in human and chimp and what’s immediately evident is that humans and chimps have DNAs that are 98% identical. They’re basically the same, there are just a couple of spelling changes. Why are there only a couple of spelling changes? Because we and chimps had a common ancestor only a few million years ago. And these few spelling differences have accumulated during the propagation of this DNA during those few million years. If more time had passed since we had our last common ancestor, more spelling changes would have accumulated.
Narrator: “If the same gene from a rat is compared, many more spelling differences are seen.”
David Page: “That’s because our common ancestor with the rat lived about 80 or 100 million years ago, and there’s been much more time for spelling differences to accumulate.”
- Cracking the Code of Life (pbs.org)