The turtle’s shell, then, is a wonderful example of exaptation—the evolutionary process where a trait evolves for one function and is then co-opted to serve another. They began as digging platforms and then became suits of armor. Feathers are another example. They now help birds to fly, but they probably originated as ways of keeping warm or signaling to mates and rivals.
How China is rewriting the book on human origins
Fossil finds in China are challenging ideas about the evolution of modern humans and our closest relatives.
.. “But it’s increasingly clear that many Asian materials cannot fit into the traditional narrative of human evolution.”
.. Stringer even suggests that H. heidelbergensis might have originated in Asia and then spread to other continents.
But many researchers, including most Chinese palaeontologists, contend that the materials from China are different from European and African H. heidelbergensis fossils, despite some apparent similarities. One nearly complete skull unearthed at Dali in Shaanxi province and dated to 250,000 years ago, has a bigger braincase, a shorter face and a lower cheekbone than most H. heidelbergensis specimens3, suggesting that the species was more advanced.
.. Politics at play?
Some Western researchers suggest that there is a hint of nationalism in Chinese palaeontologists’ support for continuity. “The Chinese — they do not accept the idea that H. sapiens evolved in Africa,” says one researcher. “They want everything to come from China.”
.. But the continuity-with-hybridization model is countered by overwhelming genetic data that point to Africa as the wellspring of modern humans. Studies of Chinese populations show that 97.4% of their genetic make-up is from ancestral modern humans from Africa, with the rest coming from extinct forms such as Neanderthals and Denisovans5. “If there had been significant contributions from Chinese H. erectus, they would show up in the genetic data,” says Li Hui, a population geneticist at Fudan University in Shanghai. Wu counters that the genetic contribution from archaic hominins in China could have been missed because no DNA has yet been recovered from them.
.. Despite the different interpretations of the Chinese fossil record, everybody agrees that the evolutionary tale in Asia is much more interesting than people appreciated before. But the details remain fuzzy, because so few researchers have excavated in Asia.
Nettie Stevens discovered XY sex chromosomes. She didn’t get credit because she had two X’s.
Wilson still believed environmental factors played a role in determining sex. Stevens said it was purely the chromosomes. Neither view could be confirmed absolutely at the time of the discovery.
.. It’s a classic case of the “Matilda effect,” a term named after the abolitionist Matilda Gage. The effect is the phenomenon that women’s accomplishments tend to be co-opted, outright stolen, or overshadowed by those of male peers. Stevens is far from the only woman scientist to have this happen to her: Rosalind Franklin, whose work was crucial to the discovery of DNA, got similarly sidelined later in the 20th century.
Dear Science: Why aren’t apes evolving into humans?
But evolution doesn’t have a destination, and even if it did, humans are certainly not it. In many cases, evolution tends to favor simplicity above all else. That’s why creatures that live in caves lose their eyes, and whales — which are descended from terrestrial mammals — have almost no leg bones. Not even intelligence is sacred: sea urchins, which have no central nervous system, evolved from an ancestor with a brain.
.. Had the climate not changed 30,000 years ago, or if it had changed differently, the Neanderthals might have survived instead of Homo sapiens.
.. Creatures like chimpanzees and bonobos are capable of building nests, using rudimentary tools, appreciating beauty, and perhaps even mourning their dead — without our energy-guzzling big brains.