By TOMOKO STEEN & WILLIAM SITTIG
Evolutionary biology as a science is based on evidence provided by both fossils and DNA, explained Bernard Wood, a world-renowned physical anthropologist, in his Oct. 24 talk at the Library of Congress, which was sponsored by the Science, Technology, and Business Division.
Wood specializes in morphological studies of human origins, but he began his lecture by stating, "Important advances in understanding human origins in the last 10 to 15 years did not necessarily come from the fossil record."
Since the 1960s, evolutionary biology has been subject to heated debates between morphologists, who base their research on the fossil data, and molecularists, who base theirs on the molecular data such as DNA and proteins. The two schools, looking at the same evolutionary pathway using these two different data, often come up with conflicting results. Wood seems open-minded about new discoveries.
Using molecular data presented in the early 1960s, Wood pointed to the fascinating finding that chimps are more closely related to humans than they are to the great apes. Reconstructions of the human line used to be only based on fragmentary fossil remains. Sometimes scientists misread the fossil record, and sometimes they were misled, as in the case of the "Piltdown Man," which is now in the history books as a great scientific hoax, he said. (See Piltdown Man, a Web site at http://home.tiac.net/~cri_a/piltdown/piltdown.html for a report, which is replete with Web links and bibliographies, about the supposed planting of hominid fossils in the Piltdown quarry, in Sussex, England.)
Wood also presented an interesting example of fossils that once were believed to be the remains of human ancestors and later found to be fossils of modern apes whose cheekbones had been eroded by the action of strong winds over many years. Wood stressed that the fossil record will always be incomplete because there is no way for scientists to know how many fossils have never been found, nor do they know exactly where to look. He added that, in any case, fossils are by nature incomplete information.
Throughout his talk, Wood reiterated three important advances in the field: (1) scientists understand considerably more than they did about the relationship of modern humans to early hominids; they know the extent to which less variable modern humans compare to their close relatives; and they know that phenotypes (morphological characteristics) are not necessarily good witnesses for genotypes (DNA and proteins). Just because two individuals look alike does not necessarily mean that they evolved from a common ancestor, he said.
As an example of the second point, Wood added that a typical troop of African monkeys contains more variability than the entire human population. Wood concluded his talk by stating that, without question, all humans are derived from African ancestors, although more investigations will be needed to truly understand man's links to the past.
Tomoko K. Steen is a research specialist, and William Sittig is chief of the Science, Technology, and Business Division.