Whenever scientists make a major discovery about human evolution, we get treated to a lot of misconceptions. The most popular of them all is the myth of the missing link—the idea that paleontologists are on an eternal quest for ancestors linking us directly back to earlier forms of life. Last May, for example, scientists reported the discovery of a 47-million-year-old fossil of a primate called Darwinius. "Fossil is evolution's 'missing link,' " blared a headline in the Sun."The beautifully preserved remains—dubbed Ida—is believed to be a direct connection between humans and the rest of the animal kingdom," the article said—a sentence that makes no sense the first time you read it and then somehow manages to make even less sense the longer you look at it.At the heart of the article is the concept of collateral ancestry as opposed to unilineal ancestry. It is the second that gives rise to the term "missing link." Such a term is ludicrous in light of what we know of how evolution proceeds. Collateral ancestry is where different related species share derived traits relative to their ancestors. An example of this would be feathers in dinosaurs and early birds. Feathers appeared in dinosaurs, likely, for insulation initially. Some of these dinosaurs went extinct but at least one branch kept evolving. This branch then, perhaps, split into two or more branches, one of which became birds. That is very simplistic but you get the idea.
It is likely that this sort of thing happened in human evolution as well, with several sister species being on the landscape at the same time, one of which gave rise to later hominids. As Berger notes, A. sediba may not be ancestral to later hominids at all. Zimmer concludes:
But that's OK. Even if A. sediba doesn't turn out to be a close relative, it gives us a glimpse at the remarkable diversity of hominins that walked the Earth 1.8 million years ago. And no matter which hypothesis wins out, A. sediba is evidence that these are exciting times to study human evolution.He is absolutely correct about that.
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