As if the jumble in cladistics of African hominins was not enough, the skull SM3, dubbed by some as “Java Girl”, adds to the bag of spanners that disrupts attempts to rationalise the human evolutionary bush (See Earth Pages Apr 2001, Skulduggery, migration and confusion). Java, of course is where the whole thing began, with Eugene Dubois’ (See Review of Pat Shipman’s biography of Dubois in Nature v. 410, p. 869) discovery of what seemed to him as Darwin’s “missing link”, in the form of Pithecanthropus (now Homo) erectus in 1892. Miss palaeo-Java, is odd by comparison, largely because her brow ridges did not meet and her forehead was “nobly” high. Morphologically, her skull shows features that could be transitional between H. erectus and H, sapiens. New Scientist ran an article (Soares, C.. Talking heads. New Sientist, 14 April 2001 issue, p. 26-29) that charts how her skull, found recently in a New York antique shop – she was smuggled out of Indonesia two decades ago, has been grist to the mill for the multiregionalists, already gleeful at the DNA sequence of Australia’s “Mungo Man” (See Earth Pages Feb 2001, Out of Africa hypothesis confounded?). Thoughtfully, Christine Soares also mentions the growing doubts that shapes of skulls and even whole skeletal anatomies can contribute a great deal resolving the multiregional vs out-of-Africa debate. This arises from Todd Disotell’s studies of modern monkeys, where he found that genetically distant species had almost identical morphologies, whereas much more closely related species were the most different from each other cranially.
Impacts and human evolution
Few Earth scientists disagree with the notion that our planet’s evolution and that of its life has been repeatedly punctuated by catastrophic impacts with comets and asteroids. The Moon’s surface is an excellent record of that bombardment in near-Earth space since about 4.45 Ga ago, when it formed in orbit around the Earth. Both dating of impact glasses from the Apollo programme and assessment of the relative ages of lunar craters provide continually refined statistics of the distribution of impact events of different magnitudes through time.
Dr Benny Peiser, a social anthropologist at Liverpool John Moores University and Michael Paine, an impact researcher from the Planetary Society in Australia, applied these statistics to the roughly 5 Ma time span of human and hominin evolution. Their suggestions were presented by Peiser at the Charterhouse Conference 2001 “Celebrating Britain’s Achievements in Space” in London (see the Cambridge Conference Network archives at http://abob.libs.uga.edu/bobk/cccmenu.html .
They calculate that 552 impacts that formed craters between 5 and more than 20 km across occurred on land during human evolution, with an additional 6 ocean impacts that could be expected to produce moderate to severe global climate disruption. So far, 32 impact craters have been discovered that are younger than 5 million years. Earth’s active erosion and sedimentation are like to have obscured more craters, even in such a brief period.
No-one would seriously dispute Peiser and Pain’s calculations, but where they proceed from them is a different matter. They assign an impact origin to the genetic bottlenecks, which seem to be implicated in speciation and which show up in modern human gene sequences (see More molecular evidence for Cro-Magnon migration into Europe – Earth Pages Jan 2001 – and Eve never met Adam – Earth Pages Nov 2000). No doubt the aftermath of sizeable impacts would place terrestrial life under considerable stress, but to jump from impact statistics to a hypothesis of external causes for hominin speciation is not likely to find much support. It does not use evidence at all, but probabilities, as often quoted that each of us is as likely to perish from extraterrestrial impact as from a firework accident or murder.
The record of human evolution is blurred to a large degree by:
1. the tiny number of fossils
2. the dates assigned to those fossils
3. the significance assigned to their morphology by different palaeoanthropologists – there are “lumpers” and “splitters”
4. the total lack of knowledge about the interplay between physiology, culture and social interaction, as regards what constituted “fitness” in natural selection.
Aside from the bottlenecks implied by modern human genetic diversity, or rather lack of it, we do not have a clue when Orrorin, “Lucy” , H. erectus, “Bonzo” the chimp or fully modern humans appeared as species. And there is another matter; the post-Miocene period has been punctuated by climatic shifts of dreadful magnitude that came thick and fast through Milankovich pacing. To suggest any other trigger for speciation, without a “smoking crater” and a precise date coinciding with the first individual of a species, is neither sensible nor necessary – as if… This is grandstanding, and the press have had a field day.
New human evolution web site
Science magazine’s NetWatch (10 April 2001) includes news of the Becoming Human web site developed by the Institute of Human Origins at Arizona State University. http://www.becominghuman.org is multimedia, including a 30 minute “webcast” by Donald Johanson, the director, who found “Lucy” in 1974. That can be skipped, and the meat found in various Exhibits, a glossary, references, links and news. The site plans to launch a teachers’ resource centre in May.