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Hunting the First Hominid

Pat Shipman

Self-centeredly, human beings have always taken an exceptional interest in their origins. Each discovery of a new species of hominid—both our human ancestors and the near-relatives arising after the split from the gorilla-chimp lineage—is reported with great fanfare, even though the First Hominid remains elusive. We hope that, when our earliest ancestor is finally captured, it will reveal the fundamental adaptations that make us us.

There is no shortage of ideas about the essential nature of the human species and the basic adaptations of our kind. Some say hominids are fundamentally thinkers; others favor tool-makers or talkers; still others argue that hunting, scavenging or bipedal walking made hominids special. Knowing what the First Hominid looked like would add some meat to a soup flavored with speculation and prejudice.

Genetic and molecular studies provide one sort of insight, showing what sort of stuff we are made of, and that it is only slightly different stuff from that which makes up the apes (gorillas, chimps, orang-utans and gibbons). From the molecular differences among the genes of humans and apes, geneticists estimate the time when each of the various ape and hominid lineages diverged from the common stem. The result is a sort of hairy Y diagram, with multiple branches instead of simply two as is usual on a Y. Each terminus represents a living species; each branching point or node represents the appearance of some new evolutionary trait, such as new molecules, new genes, new shapes or new proportions of limb, skull and tooth. Unfortunately, this way of diagramming the results tends to lull us into thinking (falsely) that all the evolutionary changes occurred at those nodes, and none along the branches.

Such studies omit a crucial part of our history: the extinct species. Only the fossil record contains evidence, in context, of the precise pathway that evolution took. In this technological age, when sophisticated instrumentation and gee-whiz algorithms seem downright necessary, the most basic information about the evolution of our lineage still comes from branches of science that operate in rather old-fashioned ways. The primary discoveries in paleontology (the study of old things), paleoanthropology (the study of old humans) and archaeology (the study of the old stuff that old humans leave around) still rely on the efforts of a handful of investigators who slog around on foot or excavate in desolate landscapes. Fancy equipment can't replace eyes and brains, although instrumentation plays a crucial role in the dating and analysis of fossil remains.

Finding the evolutionary origin of hominids is a little like stalking big game. Paleoanthropologists struggle to establish when and where their quarry was last seen and what it was like—hoping to follow its tracks backward in time. (Why hominids or any other group arose is such a metaphysical question that most paleoanthropologists run away screaming when it is asked.)

When the first hominid slinked through the underbush has been estimated from molecular clocks and confirmed by radiometric dates. These lines of evidence converge on a period between 5 million and 7 million years ago as the time when a primitive, perhaps vaguely apelike species evolved some definitive new adaptation that transformed it into the First Hominid. But like the point of inflection on a line graph, the first species in any new lineage is only readily apparent after the fact. The emergence of the first hominid was probably not obvious in prospect but only now, in retrospect—in the context of the entire evolutionary record of the hominids—when the long-term evolutionary trends can be seen.

Where this dangerous creature once lived has to be Africa, since both our closest living relatives (chimpanzees and gorillas) and all early hominids (older than about 2 million years ago) are African.

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