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Evolution of Anthropology

"In the future I see open fields for far more important researches...  Much light will be thrown on the origin of man and his history."
– On The Origin of Species
Evolution of Evolution: Interview with Integrative Biologist Tim White. Darwin's theory of natural selection included that, as humans, we have overridden natural selection because we have culture. Provided by National Science Foundation
 
With one, single sentence in "On the Origin of Species," Charles Darwin created a firestorm of debate by implying that humans evolved from animals. He wrote: Much light will be thrown on the origin of man and his history. But it was later, when German biologist Ernst Haeckel revealed a hypothetical human family tree in 1868 using 'Origin's' principles of evolution that Darwin countered with "The Descent of Man" in 1871. In it he overtly said, "The conclusion that man is the co-descendant with other species of some ancient, lower and extinct form is not in any degree new."  Since then, the human family tree has been modified again and again with some startling twists and turns.

 
Evolution of Evolution: Interview with Biological Anthropologist Ken Weiss. The 1859 book "On the Origin of Species" is notorious for Darwin's evasion of the subject of human evolution. In it, he wrote only: "much light will be thrown on the origin of man and his history." Provided by National Science Foundation
 
Audio:
Interview with Anthropologist Susan Antón
 

Essays


Skeletal Morphology
Anthropologist considers change within species over time


By Susan Antón

In "On the Origin of Species," Charles Darwin spent little time discussing fossil species but a great deal of time discussing variation in living species.  One of his key insights was recognition of the biological importance of individual variation while allowing that members of a specific species all share a 'unity of type.'  Darwin reached the critical conclusion that individual, even minor, variation was not so much 'noise' around an ideal type, but rather was important stuff upon which an individual's survival might depend.  That is, the differential survival and reproduction of particular individuals with particular kinds of variations, could, given enough time, shift the average appearance of a species by changing the frequency of certain types of variation in the population.    

There is evidence from living species that Darwin vastly underestimated the power of natural selection, and overestimated the duration of time needed to change the average morphological appearance of a species.  For example, measurable morphological change can happen between just two generations due to natural selection.  But even given this, is there evidence of gradual skeletal change in the human fossil record?

Although the fossil record forms a primary set of evidence that evolution has occurred, paleoanthropologists ironically spend infinitely more time focused on what characteristics constitute the 'unity of type' (or underlying plan) of a fossil species than they do on the all-important variation in the species.  This is in large part due to the incompleteness of the geological record and the fragmentary nature of the remains that are preserved, limitations that Darwin rightly recognized.  However, over the past 50 years, a few human lineages have yielded enough fossils that we can begin to consider individual variation and how change accumulates within a species over time.  These lineages include Australopithecus afarensis, Neandertals, and to a lesser extent, Homo erectus

Within each of these species we see evidence of significant individual variation, but also consistent change with time.  For example, in the long-lived and geographically diverse species H. erectus, brain size varies quite a bit in each geographic region.  Over the entire duration of the species (1.9 million years ago to perhaps 100,000 years ago), brain size varies from about 650 to 1250 cubic centimeters (cc).  At any given period, the difference in brain sizes is about 400 cc between the smallest and the largest individuals, but the mean value for the species increases with time.  The same is true of average brow-ridge size, which increases with time while still maintaining a fair degree of individual variation (smaller brained H. erectus also have smaller brows).  This suggests that at least some important variables increased consistently, possibly gradually, through the duration of this species.  Although this doesn't preclude the possibility that other traits might change at different paces, such evidence is consistent with Darwin's view of evolution as a slow and steady process. 

Although Homo is a relatively well-represented genus, we have little evidence about the pace of change between species because early Homo fossils, dating before the origin of H. erectus, are precious and few.However, the lineage from Australopithecus anamensis to A. afarensis seems to suggest a gradual accumulation of change in these time-successive species.

Regardless of the pace of the origin of species, understanding—as Darwin did—intraspecies variation in the context of environmental and ecological (natural selective) factors is essential to understanding our evolutionary past, as well as to providing insight into the potentials and pitfalls in the evolutionary future of our world.

Susan Antón is the joint-editor of the Journal of Human Evolution, and associate professor at the Center for the Study of Human Origins in the Department of Anthropology at New York University (NYU).  She is director of NYU's MA program in Human Skeletal Biology and recently received NYU's 'Golden Dozen' award for excellence in undergraduate teaching.  Her field research concerns the evolution of genus Homo in Indonesia and human impact on island ecosystems in the South Pacific. Her published work includes papers on the evolution of the genus Homo in Asia and Africa, for which she was elected a fellow of the American Association for the Advancement of Science (AAAS)in 2008.  The National Science Foundation supported her work on "Late Pleistocene Homo erectus in Java."

Please see the Resources section for the Bibliography/Additional Reading list for this essay.

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Darwin as Anthropologist, Anthropologists as Darwinians
Cultural evolution hinders application of natural selection to humans

By Ken Weiss

Charles Darwin avoided dealing with human origins in his "On the Origin of Species"(1859). But in "Descent of Man"(1871), he explained human physical traits in the context of primate evolution, correctly identified our African origins and stressed that human variation does not fall into a few racial categories. He offered adaptive explanations for some variable human traits like skin color, but many human traits seemed to confer no physical advantage, and he developed his theory of sexual selection to account for their evolution. In these ways, Darwin was a good anthropologist.

Biological anthropologists are committed Darwinians. We routinely use his principle of descent with modification from a common ancestor in our research, and we integrate genetic, geographic, geologic and fossil data to reconstruct the evolutionary history of primates, including ourselves. We can compare human and other primate DNA sequences to search for aspects of our genome that may reflect natural selection which occurred specifically in our human lineage. Genes that contribute to the adaptive evolution of several relatively simple human traits like skin color or resistance to malaria have been identified.

However, the theory of natural selection presents subtle and difficult problems for anthropology. Darwin wrote that he over-stressed natural selection to show that historical processes alone could account for human origins. In "Expression of the Emotions in Man and Animals"(1872), he used cross-cultural data to identify human behavioral universals in order to show that our species had a single evolutionary origin. He abstained from offering selective explanations in that book, but in "Descent of Man," he identified important behavioral questions whose evolution is difficult to explain, such as traits like celibacy or self-sacrifice for others, in which individuals seem to voluntarily short-change their own biological interests. The evolution of such traits is still discussed today, and some of Darwin's ideas accepted. 

Darwin recognized the difference between cultural and biological evolution, but he indulged in rather ethnocentric and unsupported speculation about how natural selection made people in 'civilized' cultures superior to people in less technically complex cultures. Proper recognition of Darwin's legacy must acknowledge that, from his time to the present, it has been easy to be so Darwinian that we incautiously assert what natural selection may have favored in human groups or individuals, making us lesser anthropologists due to the fact that differences may more likely be simply cultural. The value judgments resulting from such speculation have been misused to justify social inequality, racism, eugenics and even genocide.

Ironically, Darwin himself became a lesser Darwinian by saying that modern societies are exempt from the otherwise universal applicability of natural selection, because culture can overcome environments and protect the weak. This overlooks the central fact that culture has always been part of the uniquely adaptive context that made us human, and culture has always covered for traits that would otherwise be weak or harmful. 

Darwin transformed our view of ourselves. The great genius of his ideas was their elegant simplicity. But genetic research has shown that both natural selection and the causal connections between genes and the traits that evolution has produced are usually weak, complex and difficult to identify, in part because of our inherently interwoven, ever-changing biocultural evolution. The best way to honor Darwin will be to develop a more integrated anthropology, a challenge that will keep anthropology vibrant for another 150 years.

Ken Weiss is the Evan Pugh Professor of Biological Anthropology and Genetics at Penn State University in University Park, Penn. He is the author of several books, including "Demographic Models for Anthropology;" "Genetic Variation and Human Disease: Principles and Evolutionary Approaches;" "The Mermaids Tale: Four Billion Years of Cooperation in the Making of Living Things," with Anne V. Buchanan; and "Genetics and the Logic of Evolution," also with Buchanan.  His work consists of more than 250 journal articles covering topics such as evolutionary and developmental genetics, complex biological traits and human variation, evolutionary principles, and the philosophy and societal implications of biology. He writes "Crotchets and Quiddities," a regular column on evolutionary topics, for the journal Evolutionary Anthropology.

Please see the Resources section for the Bibliography/Additional Reading list for this essay.

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Human Evolution's Winding Path:
Darwin got it mostly right

By Tim White

The 1859 book "On the Origin of Species" is notorious for Darwin's evasion of the subject of human evolution. In it, he wrote only: "much light will be thrown on the origin of man and his history." However, Darwin more directly discussed the subject of human evolution in his 1871 treatise, "The Descent of Man." In that book, he clearly laid out a prediction that human ancestors would be found in Africa. Of course, at the time, there was virtually no known fossil record, so Darwin could only predict that someday, some "future geologist" would find fossils connecting modern apes with modern humans via an ancient undiscovered common ancestor. These predictions proved to be remarkably accurate.

Based on what was known at the time about living apes and humans, Darwin 'triangulated' that our earliest hominid ancestors were the result of feedback between bipedality, freedom of the hands, reduction of the canine tooth and face, expansion of the brain, and the increasing use of tools. In other words, he postulated simple, straight-line, human evolution. In the 138 years that followed, however, evidence showed this model was too simplistic as the fossil record revealed a more complicated path to modern humans.

Prehistoric stone tools were found across Europe long before Darwin and his contemporary British naturalist Alfred Russel Wallace explained evolution via the mechanism of natural selection. Accompanying some of these tools were human-like fossils that took their name from Neanderthal, the German site where they were first discovered.  The "Neanderthal Men" associated with the site became one of the earliest challenges to Darwin's view of human evolution. Neanderthals were interpreted by some as pathological, whereas others saw them as an evolutionary side branch, and yet others as direct human ancestors. The Neanderthal debate persisted for nearly 150 years, and was only recently resolved by a powerful combination of well-dated African fossils and comparisons of ancient Neanderthal DNA with DNA of modern humans. Evidence now indicates these near-humans were a circum-Mediterranean side branch that went extinct about 30,000 years ago and did not give rise to modern humans.

Neanderthals show that the path to modern humans was not the simple, straight-line predicted by Darwin, since they existed too recently to bear on Darwin's predictions about what our much earlier progenitors were like, or where they lived. However the recovery of well-preserved fossils in a well-calibrated, dated geological sequence largely have proved Darwin's original hypothesis about an African birthplace. These early human-like fossils first were discovered in the 1920s, in Africa, as Darwin predicted. At first there was considerable controversy over these remains. Today, however, we recognize several species that all belong within Australopithecus, a zoological genus closely related to the human genus Homo—and seemingly ancestral to it. Perhaps the most important of the thousands of Australopithecus fossils known today is a small female found in the Ethiopian desert. Her scientific name is Australopithecus afarensis, and she died 3.2 million years ago. Her bones eventually eroded out of ancient channel deposits and her discoverers nicknamed her "Lucy." The completeness and quality of her skeleton has provided considerable insight into early hominids. On the family tree, Lucy's species is one of many now bridging the gap between modern people and the last common ancestor that we shared with the living African apes.

Science has both creative and critical dimensions. Darwin, as a historical scientist, employed what he knew about the modern world to predict what might have been found in the world of the past. He creatively and correctly hypothesized that humans evolved in Africa. He creatively but incorrectly hypothesized that our earliest ancestors would appear to be a halfway house between chimpanzee and human. The evidence of Lucy and the many other fossils of the species that she represents shows that these creatures were neither chimps nor humans, nor were they halfway between modern chimpanzee and human, but rather had their own unique characteristics. This uniqueness is confirmed by evidence of the archaeological record as well as geochronology. The molecular evidence also confirms this in the living endpoints of two very different evolutionary trajectories.

Although Darwin's hypothesis on the location of the evolution of man has proven correct, Darwin's hypothesis about the sequence in which human characteristics arose during our evolution has been rejected. It seems likely that Darwin would have been delighted to witness the arrival and interpretation of that new evidence. The approach that he brought us—how to be curious, critical and creative scientists—has indeed seen evolutionary biology through the last 150 years very nicely. Darwin's core insight lets us understand how evolution works and is now the bedrock of biology. It is also the very basis for understanding how we got here.

Tim White is a world renowned paleoanthropologist and professor of Integrative Biology at the University of California at Berkeley. His work frequently takes him to study sites in Afar, Ethiopia, Jordan, Kenya, Malawi, Tanzania (at Olduvai Gorge and Laetoli) and Turkey. His primary research involves human evolution in all its dimensions and he and his colleagues are credited with the discovery in Ethiopia in 1995 of perhaps the oldest known human ancestor, Ardipithecus ramidus, dated to 4.4 million years ago. The National Science Foundation supports his work on a Middle Awash research project in Ethiopia.

Please see the Resources section for the Bibliography/Additional Reading list for this essay.

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