In family terms, is the woman in that ancient photo your great-great aunt or your great-great-grandma?
In a Wired article of enduring interest (“Ancestor Worship,” February 22, 2011), science writer Brian Switek recounts the chances of getting it wrong, with an episode from the life of Darwin’s bulldog, T. H. Huxley,
In his 1870 address as the president of London’s Geological Society, the naturalist Thomas Henry Huxley reminded his colleagues that creatures which appeared to be perfect transitional forms between one species and another might – upon accumulation of further evidence – turn out to be cousins or uncles rather than fathers. A fossil animal with transitional features undoubtedly attested to the reality of evolution, “But the mere discovery of such a form does not, in itself, prove that evolution took place by and through it.”
Huxley learned this the hard way a few years later. During his 1870 address, he proposed that paleontologists had directly connected the modern horse Equus to at least two of its fossil predecessors – the three-toed horse Hipparion and the even older fossil equid Anchitherium. Both of these horses were found in Europe – confirming that horses were animals of the Old World – but a stunning collection of fossil horses collected by American paleontologist Othniel Charles Marsh proved Huxley wrong. Marsh’s collection confirmed that horses originated in North America, and the supposed transitional forms Huxley cited were species that had dispersed to Europe at different times. Huxley saw these fossils for himself when he visited Marsh at Yale’s Peabody Museum during an 1876 speaking tour, and he immediately changed his lecture to include Marsh’s discoveries.
The factors that led Huxley to misread the evolution of horses have also confounded the study of human origins. The most obvious is the elusiveness of the creatures that fill out the evolutionary transition. Fossil humans are very rare. The earliest humans, especially, lived in forests where their bodies were much more likely to be destroyed than quickly preserved. As a result, we are always working with an imperfect record, and therefore it is easy to take a species that appears to fill a gap in our knowledge and promote it as ancestor of something else. More.