When Australopithecus ramidus was the missing link

Ann Gibbons is a science writer specializing in paleoanthropology for the journal, Science. Her 2006 book, The First Human: The Race to Discover Our Earliest Ancestors gives an account of the discovery of African fossil hominins from the early 1990s up to the early 2000s. This time provided some of the most contentious discoveries ever by characters like Tim White, Michel Brunet, and Maeve Leakey, and Gibbons covered the field for one of the main journals publishing hominin fossil remains.

On page 145, Gibbons describes a problem that emerged at the publication of Australopithecus ramidus in 1994 by Tim White and colleagues. The paper was published together with a two-page perspective article by Bernard Wood. Wood reviewed the major findings of the description of Au. ramidus and the accompanying article on the geological context of the find by Giday WoldeGabriel and colleagues. He ended his piece with a piece of hyperbole:

The metaphor of a "missing link" has often been misused, but it is a suitable epithet for the hominid from Aramis.

“Missing link” is a term that has led to terrible misconceptions about the evolutionary process. Probably the worst is that every fossil hominin must have its proper place on a single evolutionary chain. In reality, paleontologists work to discover cousins, some of which may be ancestors of later forms, but many of which are not. It is by understanding the phylogenetic relationships among these fossils that we can test hypotheses about their common ancestors. This is why evolutionary biologists do not use the term “missing link”—and why creationists work so diligently to lead religious adherents to believe that “missing links” are all we are trying to find.

As Gibbons describes, the idea that Au. ramidus was “the missing link” was widely reported in the press and supported by the idea that it was an early representative of a single lineage of hominins in the early phases of human evolution:

Nature showed little restraint in its promotion of the seventeen fossils from Aramis as "a missing link," and newspaper and magazine headline writers took the additional step of ignoring the qualifying article, "a." The news made the front pages of newspapers in London, New York, San Francisco, and around the world. The headline in the Times of London was typical, calling it THE BONE THAT REWRITES THE HISTORY OF MAN. More than one article said that the new fossil supported the view that there was a single line if descent from chimpanzees to humans, with diagrams of family trees showing A. ramidus as the direct ancestor of Lucy's species, A. afarensis, and giving rise to all the different types of hominids that came later. It was pleasing in its clarity and logic. Lucy's discoverer, Donald Johanson, would be quoted in the Los Angeles Times as saying that beyond 4 million years ago there appears to be "a single line and a single lineage." Even [Tim] White would invoke the image of a missing link, saying that this new species of hominid was the "oldest known link in the evolutionary chain that connects us to the common ancestor with the living African apes. The discovery takes us one major step closer to this common ancestor."

Less than a year after the publication of their description, White and colleagues would provide an erratum claiming that the Aramis fossils should be placed into a different genus, Ardipithecus (White et al. 1995). But as quoted by Blake Edgar at that time (1995), his attitude about the evolutionary chain was not changed by the new name:

"Ramidus is a link, but it's no longer missing," says White. "This discovery is important because it gives us our first good look at the biology of a very ancient ancestor that sits at the root of the family tree."

The idea that Ar. ramidus may be a direct ancestor of living people has not entirely gone away; White and colleagues (2009) presented it as one of three hypotheses about the relationships of the species. The concept of “ancestor” creates its own special problems: Paleoanthropologists like White often use it very broadly to refer to fossil hominins without special regard to whether those precise fossils or their population are actually ancestors of later hominins. The case of Ardipithecus has raised this problem more than most, and I’ll come back to that point later.

References

Edgar, B. (1995). Digging up the family bones. BioScience, 659-662.

Gibbons, A. (2007). The first human. Knopf-Doubleday Publishing Group, New York.

White, T. D., Suwa, G., & Asfaw, B. (1994). Australopithecus ramidus, a new species of early hominid from Aramis, Ethiopia. Nature, 371(6495), 306. doi:10.1038/371306a0

White, T. D., Suwa, G., & Asfaw, B. (1995). Australopithecus ramidus, a new species of early hominid from Aramis, Ethiopia. Nature, 375(6526), 88.

White, T. D., Asfaw, B., Beyene, Y., Haile-Selassie, Y., Lovejoy, C. O., Suwa, G., & WoldeGabriel, G. (2009). Ardipithecus ramidus and the paleobiology of early hominids. science, 326(5949), 64-86. doi:10.1126/science.1175802

WoldeGabriel, G., White, T. D., Suwa, G., Renne, P., de Heinzelin, J., Hart, W. K., & Heiken, G. (1994). Ecological and temporal placement of early Pliocene hominids at Aramis, Ethiopia. Nature, 371(6495), 330-333. doi:10.1038/371330a0

Wood, B. (1994). The oldest hominid yet. Nature, 371(6495), 280-281. doi:10.1038/371280a0