Human ancestors make evolutionary changes.Human Ancestors Make Evolutionary Change
Some scientists believe that Homo erectus Homo erectus (hō`mō ērĕk`təs), extinct hominid living between 1.6 million and 250,000 years ago. Homo erectus is thought to have evolved in Africa from H. habilis, the first member of the genus Homo. , the species directly ancestral to modern humans, is a model of evolutionary stability and a prime example of the theory of "punctuated equilibrium punc·tu·at·ed equilibrium
The theory that speciation occurs in spurts of major genetic alterations that punctuate long periods of little change. ,' which holds that individual species have a clear beginning and end (SN: 7/25/81, p. 52). This view was fostered by a recent study indicating that for nearly 1.5 million years these precursors of Homo sapiens Homo sapiens
(Latin; “wise man”)
Species to which all modern human beings belong. The oldest known fossil remains date to c. 120,000 years ago—or much earlier (c. remained largely the same, rapidly changing in form and developing larger brains only when a new species was about to appear.
Several lower forms of life are undoubtedly marked by long periods of relatively little change followed by rapid transformations into new species, a cornerstone of punctuated equilibrium theory, but this pattern clearly does not apply to H. erectus, contends an anthropologist who recently trekked throughout the world to survey all known H. erectus specimens. "It appears that there are significant evolutionary changes within a conservatively defined sample of H. erectus,' says Milford H. Wolpoff Milford H. Wolpoff (born 1942 to Ruth (Silver) and Ben Wolpoff, Chicago) is a paleoanthropologist, and since 1977, a professor of anthropology and adjunct associate research scientist, Museum of Anthropology at the University of Michigan. of the University of Michigan (body, education) University of Michigan - A large cosmopolitan university in the Midwest USA. Over 50000 students are enrolled at the University of Michigan's three campuses. The students come from 50 states and over 100 foreign countries. in Ann Arbor Ann Arbor, city (1990 pop. 109,592), seat of Washtenaw co., S Mich., on the Huron River; inc. 1851. It is a research and educational center, with a large number of government and industrial research and development firms, many in high-technology fields such as .
Wolpoff, whose research itinerary included stops in China, Indonesia and North America, took a variety of skull, jaw and dental measurements from 92 of these "prehumans.' He divided the specimens, which date from about 1.4 million years old to 400,000 years old, into early, middle and late H. erectus groups. Averages of the measurements for each group were compared across the 1-million-year span.
With only a few exceptions, he found pronounced differences between the early and late H. erectus samples. The changes are in the direction of a modern profile, reports Wolpoff in the justreleased Fall 1984 PALEOBIOLOGY pa·le·o·bi·ol·o·gy
The branch of paleontology that deals with the fossils of plants, animals, and other organisms.
pa ; cranial capacity expands while jaw and tooth size shrinks. The few skull and jaw features that remain stable do not detract from the evidence that two major "adaptive systems' of the H. erectus lineage changed substantially over time, he says.
Wolpoff also studied 13 individuals who are either late H. erectus or early H. sapiens sa·pi·ens
Of, relating to, or characteristic of Homo sapiens.
[Latin sapi . There is no distinct boundary between the two species, he says, again suggesting that in this case punctuated equilibrium theory does not apply. That theory, as proposed in 1977 by Stephen J. Gould of Harvard University and Niles Eldredge of the American Museum of Natural History American Museum of Natural History, incorporated in New York City in 1869 to promote the study of natural science and related subjects. Buildings on its present site were opened in 1877. in New York City New York City: see New York, city.
New York City
City (pop., 2000: 8,008,278), southeastern New York, at the mouth of the Hudson River. The largest city in the U.S. , assumes that there are clear demarcations between successive related species, and that evolutionary changes are often spontaneous responses to unexpected environmental demands. The continuous, although not necessarily constant, rates of change within H. erectus do not reflect this assumption, adds Wolpoff.
Gould and Eldredge first used H. erectus as an example of their theory following a 1981 report by G. P. Rightmire of the State University of New York at Binghamton Binghamton University, State University of New York, or their officially adopted name, Binghamton University, is a coeducational public research university located in Vestal, New York. . He studied 65 individuals designated as H. erectus and concluded that the species did not significantly evolve over time.
But Rightmire's study is seriously flawed, says Wolpoff. Up to 16 of the specimens he used may not be H. erectus, and his statistical analysis was not adequate to uncover evolutionary changes.
Rightmire acknowledged to SCIENCE NEWS that he would take a different statistical approach if he conducted a new study. "But it's difficult to see [Wolpoff's study] as a coherent statement on the entire species,' he argues. "Wolpoff is hardly following a conservative approach to defining H. erectus.'
When two specimens that may not be H. erectus are taken out of Wolpoff's early sample and another is removed from the late sample, there is no statistically meaningful difference between the cranial capacities of the two groups, says Rightmire. "There are signs of rapid evolutionary change, especially in brain size, as Homo erectus gave way to Homo sapiens, although this does not necessarily mean there was a branching of species as punctuated equilibrium theory predicts.'
"[Rightmire] is absolutely wrong,' responds Wolpoff. There is no justification for removing the three specimens from the study, he says, but even without them the sample is large enough to be unaffected by the loss of a few individuals.
"The more interesting issue now is to examine the speed and direction of evolutionary change in Homo erectus,' says Wolpoff.
Adds Philip D. Gingerich, director of the Museum of Paleontology paleontology (pā'lēəntŏl`əjē) [Gr.,= study of early beings], science of the life of past geologic periods based on fossil remains. at the University of Michigan: "I think Wolpoff was quite conservative in his definitions of which specimens are Homo erectus. We always want more details, but his study is a step above anything that has been done before.'
Photo: Skull of a 1.6 million year old H. erectus youth, discovered after Wolpoff's survey.