A recent article in TIME magazine ("Evolving Darwin," by Carl Zimmer, February 23, 2009, issue) about Darwin's theories and scientists' more recent findings using DNA had some rare gems in it that I'd like to share. The basis of the article is a book -- Why Evolution is True -- by Jerry Coyne, an evolutionary biologist a the University of Chicago.
Note that Darwin's theories were first published in his book On the Origin of Species on 24 November 1859. In it he recognized that
variation and heredity were the twin engines that made evolution possible, [but] he didn't know what made them possible. It would take almost a century after the publication of On the Origin of Species for biologists to determine that the answer was DNA.
DNA is like a genetic cookbook, using four molecular "letters" to spell out recipes for everything from hormones to heart valves...
Time and again, biologists are finding that Darwin had it right: evolution is the best way to explain the patterns of nature.
Here's a compendium of nuggets from the article:
- Besides studying fossils, biologists can discover the genealogy of species by looking at their DNA. The fossil record points to hippos and other hoofed mammals as being the closest living relatives of whales. So does their DNA. Our own DNA contains clues to the bonds we share with the rest of life — it turns out, for instance, that we are closer kin to mushrooms than to sunflowers.
- In fact, a lot of mutations that all humans carry neither helped nor harmed our ancestors. They spread just by chance. And a lot of our genome is not made up of protein-coding genes. In fact, 98.8% of it is not. Some of that 98.8% consists of "pseudogenes" — genes that once encoded proteins but no longer can because of a crippling mutation. They are the molecular equivalent of a vestigial tail, allowing us to see evolution's track.
- [Referring to Darwin's metaphor for evolution, the tree of life] ... there's more to the history of life than the branching of a tree. Viruses ferry genes from one host to another. Bacteria swap genes inside our bodies, evolving resistance to antibiotics in our own gut. Some 2 billion years ago, one of our single-celled ancestors took in an oxygen-consuming bacterium. That microbe became the thousands of tiny sacs found in each of our cells today, known as mitochondria, that let us breathe oxygen. When genes move this way, it's as if two brances of the tree of life are being grafted together.
- There are 10,000 species of bacteria in a spoonful of dirt, twice as many species as all the mammals in the world.
This article also contains a table comparing Darwin's theory to current findings, here quoted:
| Darwin |
|
Today [in DNA] |
| Species share a common ancestry, like branches on a tree |
|
Genetic studies confirm that different species have evolved from common ancestors. But DNA has also jumped from one species to another — turning parts of the tree of life into a web |
| Humans evolved from apes in Africa |
|
Evidence from DNA indicates that chimpanzees and bonobos are the closest living relative to humans. Fossils document the course of human evolution in Africa from apelike ancestors over the past 7 million years |
| Natural selection is a powerful force driving evolution |
|
Natural selection's fingerprints can be detected in the human genome. But many mutations have spread thanks to pure chance (a process know as genetic drift) |
| Complex traits like eyes can evolve through a series of intermediate steps |
|
Fossils have documented some of those steps in structures such as limbs and ears. Studies on DNA have shown how genes for building old organs have been "borrowed" to help build new ones |
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