The Origin of Humankind [1994, 2008] by Richard Leakey

Author:Richard Leakey [Leakey, Richard]
Language: eng
Format: epub
Publisher: Basic Books
Published: 1994-10-06T16:00:00+00:00

FIGURE 5.1

Neanderthal relations. Neanderthals share some features with Homo sapiens, such as a large brain, and some with Homo erectus, such as a long, low skull and prominent brow ridges. They have many unique features, however, the most obvious of which is extreme protrusion of the midfacial region.

Culture represents a novelty in the world of nature, and it could have added an effective, unifying edge to the forces of natural selection. Moreover, Christopher Wills, a biologist at the University of California, Santa Cruz, identifies the possibility here of an accelerating pace of evolution. In his 1993 book The Runaway Brain, he notes: “The force that seems to have accelerated our brain’s growth is a new kind of stimulant: language, signs, collective memories—all elements of culture. As our cultures evolved in complexities, so did our brains, which then drove our cultures to still greater complexity. Big and clever brains led to more complex cultures, which in turn led to yet bigger and cleverer brains.” If such an autocatalytic, or positive feedback, process did occur, it could help promulgate genetic change through large populations more rapidly.

I have some sympathy with the multiregional evolution view, and once offered the following analogy: If you take a handful of pebbles and fling them into a pool of water, each pebble will generate a series of spreading ripples that sooner or later meet the oncoming ripples set in motion by other pebbles. The pool represents the Old World, with its basic sapiens population. Those points on the pool’s surface where the pebbles land are points of transition to Homo sapiens, and the ripples are the migrations of Homo sapiens. This illustration has been used by several participants in the current debate; however, I now think it might not be correct. One reason for my caution is the existence of some important fossil specimens from a series of caves in Israel.

Excavation at these sites has been going on sporadically for more than six decades, with Neanderthal fossils being found in some caves and modern human fossils in others. Until recently, the picture looked clear and supported the multiregional-evolution hypothesis. All the Neanderthal specimens—which came from the caves of Kebarra, Tabun, and Amud—were relatively old, perhaps some 60,000 years old. All the modern humans—which came from Skhul and Qafzeh—were younger, perhaps 40,000 to 50,000 years old. Given these dates, an evolutionary transformation in this region from the Neanderthal populations to the populations of modern humans looked plausible. Indeed, this sequence of fossils was one of the strongest pillars of support for the multiregional-evolution hypothesis.

In the late 1980s, however, this neat sequence was overturned. Researchers from Britain and France employed new methods of dating, known as electron spin resonance and thermoluminescence, on some of these fossils; both techniques depend on the decay of certain radioisotopes common in many rocks—a process that acts as an atomic clock for minerals in the rocks. The researchers found that the modern human fossils from Skhul and Qafzeh were older than most of the Neanderthal fossils, by as much as 40,000 years.

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