Physical Anthropology Update

Philip L. Stein & Bruce M. Rowe

Number 6 Fall 1997


Copyright © 1997 by McGraw-Hill, Inc. All rights reserved. Printed in the United States of America. The entire contents or parts of this Update may be reproduced for use with Physical Anthropology, Sixth Edition, or Physical Anthropology: The Core, second edition, by Philip L. Stein and Bruce M. Rowe, provided each reproduction bears the copyright notice. The publisher's written permission must be obtained for other use.

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CONTENTS
"Neandertal Park" Another New Hominid Ancestor-Maybe
The Ups and Downs of Hominid Height Dolly's "Sister"-Polly
An Early Old World Monkey Oldest Hunting Weapon Reported
"Mitochondrial Rover" Origins of Domestication in the New World
Physical Anthropology Web Sites

"NEANDERTAL PARK"

See Physical Anthropology, 6th edition, Chapter 17, page 438; Physical Anthropology: The Core, Chapter 11, pages 260-261.

The plot of the highly successful movie "Jurassic Park" is based upon the premise that prehistoric DNA can be removed from dinosaur blood from the intestinal tract of prehistoric insects trapped in amber. This conjecture has been pretty well discounted lately. Researchers have concluded that the alleged DNA sequences from these samples are artifacts of the extraction process and that over the millions of years since the death of the insects the DNA has degraded.

Still, under some circumstances DNA does remain in ancient bone, but only bone of relatively recent derivation. One possible study would be of human fossils from the past 100,000 years. Recently a 3.5 gram sample of bone was removed from the right humerus of the original Neandertal material discovered in 1856 the Neander Valley of Germany. Using extremely careful laboratory procedures, the investigators were able to isolate a sequence of the hypervariable region I of mitochondrial DNA. Because this region is associated with fairly rapid mutation rates, differences in the sequence of nucleotides will show up in relatively closely related populations.

The mtDNA sequence isolated from the Neandertal material includes 360 base pairs. When the Neandertal mtDNA sequence is compared to the modern human reference sequence, there are 27 differences. Of the 27 differences, 24 are transitions, that is, a substitution of one pyrimidine (C or T) for the other or a substitution of one purine (A or G) for another. Another 2 differences are transversions, that is, a substitution of a pyrimidine by a purine or a purine by a pyrimidine. Finally, there is one insertion of an adenosine residue (that is, a nucleotide with an A).

Next, the mtDNA sequence was compared with 2051 modern human and 59 chimpanzee sequences, with the following results:

average number of differences:
among the modern human mtDNA lineages 8.0
between Neandertal and modern human mtDNA lineages 25.6
between modern human and chimpanzee mtDNA lineages55.0
From this data we see that the average number of differences in the mtDNA sequences between modern humans and Neandertals is three times that among modern humans. Also, the average number of differences between modern humans and chimpanzees is about twice that of modern humans and Neandertals.

The Neandertal sequence was then com-pared with a series of human mtDNA lineages from different parts of the world. The mean differences are:

European 28.2 substitutions
African27.1 substitutions
Asian27.7 substitutions
Native American 27.4 substitutions
Australian/Oceanic28.3 substitutions

One of the major areas of disagreement among paleoanthropologists is whether or not the Neandertal gene pool contributed to the gene pool of modern Homo sapiens. If this were true, we would expect the number of substitutions between the Neandertal and European mtDNA to be significantly less than that between the Neandertal and other mtDNA lineages. The data clearly shows that this is not the case. In fact, when this data is used to build a phylogenetic tree, we can only conclude that modern H. sapiens originated in Africa.

DATING THE DIVERGENCE

One of the more controversial aspects of DNA studies is the dating of the divergence of two DNA lineages. Determining the timing of the molecular clock is based upon the idea that substitutions in the DNA sequence occur on a regular basis, and that time is directly proportional to the number of nucleotide substitutions. The problem is that the rates of substitutions, and hence the molecular clock, differs in various segments of the genome and in different species.

Paleoanthropologists generally agree that the divergence between modern humans and chimpanzees occurred around 5 to 4 million years ago. Using that date in association with the number of substitutions between modern human and chimpanzee mtDNA, the investigators estimate that the divergence between Neandertal and modern human mtDNA, that is the date of the most recent common sequence, falls between 690,000 and 550,000 years ago. Using the same molecular clock, the common ancestor of all modern human mtDNA falls between 150,000 and 120,000 years. Of course we have to be very careful about these dates, for they are only as good as the estimated divergence date of humans and chimpanzees.

CONCLUSION

The study of Neandertal mtDNA is very interesting and supports the contention of those paleoanthropologists who propose that the Neandertals are a distinct species that did not contribute to the gene pool of modern Homo sapiens sapiens. It appears that the Neandertals split off from the lineage leading to modern humans over 500,000 years ago. Chris Stringer suggests that the Middle Pleistocene species Homo heidelbergensis was the common ancestor of the Homo neandertalensis and Homo sapiens. The Neandertals then become extinct without contributing any significant genetic material to the modern human gene pool.

Chris Stringer suggests a date for the divergence of modern humans and Neandertals between 300,000 and 250,000 years ago based upon the morphology of the available fossils. This is consistent with the archaeological data. This does not contradict the earlier date for the divergence of the mtDNA since a genetic divergence would be expected to proceed the evolution of distinct morphological and behavior features by a significant period of time.

A major problem is that this study is based upon a single sample. At least one additional study of another Neandertal fossil from a different part of Europe or western Asia needs to be done. But such a study must be approached with caution since fossil material is destroyed in the process.


Sources: M. Krings, et al., "Neandertal DNA Sequences and the Origin of Modern Humans," Cell, 90 (July 11, 1997), 19-30; T. Lindahl, "Facts and Artifacts of Ancient DNA," Cell, 90 (July 11, 1997), 1-3; R. Ward and C. Stringer, "A Molecular Handle on the Neanderthals," Nature, 388 (17 July 1997), 225-226; C. Stringer, "Chronological and Biogeographic Perspectives on Later Human Evolution," in O. Bar-Yosef and T. Akazawa (eds.), Neanderthals and Modern Humans in West Asia (New York: Plenum, in press).

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ANOTHER NEW HUMAN ANCESTOR-MAYBE

See Physical Anthropology, 6th edition, Chapter 17 and 18; Physical Anthropology: The Core, 2nd edition, Chapter 12 and 13.

Not so long ago, most anthropologists spoke of three species of the genus Homo: H. habilis, H. erectus, and H. sapiens. More recently additional species of Homo have been proposed, which suggests a more complex evolutionary history for our genus. These include H. rudolfensis, H. ergaster, and H. heidelbergensis. The latter species is used by some paleoanthropologists for a collection of fossils from Europe and Africa that date between 600,000 and 200,000 B.P. Now a new species of Homo has been proposed-Homo antecessor.

H. antecessor fossils have been recovered at the cave site of Gran Dolina in the Atapuerca Hills of northern Spain. These fossils, which may be more than 780,000 years old, are the earliest hominid remains in Europe. The new species designation is based primarily on a partial juvenile facial skeleton. Prior to the discovery of these fossils, European hominids were attributed to H. erectus dating to about 500,000 years ago.

To the discoverers, including Jose Maria Bermúdez de Castro of the National Museum of Natural Sciences in Madrid, H. antecessor may represent the common ancestor of modern humans and the Neandertals. Bermúdez de Castro and his colleagues describe the juvenile as having a very modern looking face, but a primitive jaw and brow. They suggest that H. ergaster, through traditional forms, evolved into H. antecessor. Different populations of H. antecessor, in turn, evolved into H. sapiens and the Neandertals. In this scheme Neandertals are placed into the species H. neandertalensis. If this is correct, than H. erectus is not a direct ancestor to H. sapiens; H. erectus is a side branch of hominid evolution that evolved from H. ergaster between 1.8 and 1.6 million years ago. In this scheme H. heidelbergensis is ancestral only to the Neandertals and not a common ancestor of both H. sapiens and the Neandertals. However, as with all new discoveries and reinterpretations of the hominid family tree, there are many disagreements over the new interpretation.

Source: J. M. Bermudez de Castro, et al., "A Hominid from the Lower Pleistocene of Atapuerca: Possible Ancestor to Neandertals and Modern Humans, Science, 275 (May 30, 1997), 1392-1395; A. Gibbons, "A New Face for Human Ancestors," Science, 275 (May 30, 1997), 1331-1333.

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THE UPS AND DOWNS OF HOMINID HEIGHT

See Physical Anthropology, 6th edition, Chapters 16-19; Physical Anthropology: The Core, 2nd edition, Chapters 11-13.

The traditional view of hominid stature is that as hominids evolved from prehominid ancestors to H. sapiens, each genus and species progressively got taller and larger brained. Some doubt had been cast on this generality with the realization that one early Homo fossil ("Turkana Youth"), dated at about 1.6 million B.P., represented an individual who might have grown to over 6 feet tall if he had lived to adulthood.

Recently, Christopher Ruff, Eric Trinkaus, and Trenton Holliday have used two different measures of body mass on 163 Pleistocene members of the genus Homo. These individuals lived between 1.8 million and 36,000 years ago. In comparing these fossils with contemporary humans, they found that the body mass of the fossil hominids gradually increased over time and was, on the average, 12.7 percent greater than the average for modern peoples. Neandertals were about 24 percent larger than modern humans living at the same latitudes.

In this same study, the investigators found that brain size relative to body size remained constant from about 1.8 million to about 600,000 years ago. Then, relative brain size began to increase until about 35,000 to 30,000 years ago. Since that time, brain size has declined by about 10 percent in comparison with early modern humans such as those found at the sites of Skh_l and Qafzeh in Israel and the Cro-Magnon rock shelter in France.

There are many reasons why such a decline in body mass and relative brain size may have occurred in recent modern people. New technologies that developed in the Upper Paleolithic and later may have reduced the selective advantage of brawn in some way while increasing the selective advantage of brain power. However, brain size was also decreasing. The decrease in brain size is not necessarily associated with a decrease in intellectual abilities. Also, as humans developed domestication, nutrition actually worsened. Eric Trinkaus suggests that poor nutrition could have contributed to a decline in body mass in recent modern peoples.

John Kappelman believes that the conclusions that Ruff's and his colleagues' make may have merit. Yet he also points to some possible problems in the calculations. He suggests that the modern humans used for comparisons should be athletes. They would be a better match for hunters, scavengers, and gatherers of the past, as opposed to more sedentary peoples. Also, 87 percent of the 163 fossils used are from the last 200,000 years. Finally, there are questions of sampling error with the estimates of body size and brain size. In most cases, the crania and postcranial materials do not come from the same individual.

Sources: C. B. Ruff, E. Trinkaus, and T. W. Holliday, "Body Mass and Encephalization in Pleistocene Homo," Nature, 387 (May 8, 1997), 173-176; J. Kappleman, "They Might be Giants," Nature, 387 (May 8, 1997), 126-127; A. Gibbon, "Bone Sizes Trace the Decline of Man (and Woman)," Science, 276 (May 9, 1997), 896-897.

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Dolly's "Sister"-Polly

In the last Update we reported the birth of the sheep Dolly, the first animal to be cloned from a cell of an adult animal. At about the same time, three other sheep were born that were cloned from fetal cells.

On July 24, 1997, five more sheep were born cloned from fetal cells and carrying extra genes. Among these extra genes were human genes that were introduced into the fetal cells before they were cloned. In the future is may be possible to design domesticated animals capable of producing human gene products.

Source: E. Pennisi, "Transgenic Lambs from Cloning Lab," Science, 277 (August 1, 1997), 631.

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AN EARLY OLD WORLD MONKEY

See Physical Anthropology, 6th edition, Chapter 15, pages 387-388; Physical Anthropology: The Core, 2nd edition, Chapter 10, page 226.

Much of the evolutionary history of the anthropoids has to be reconstructed from bone fragments and teeth. Therefore, a recovery of a complete and undistorted skull represents a highly significant event, especially since it is the only specimen of this quality that has been discovered between the middle Oligocene and the late Miocene. The early Old World monkeys, the Cercopithecidae from the Miocene, are commonly assigned to the family Victoriapithecidae. Although known from several hundred fragmentary finds, this new discovery of a Victoriapithecus skull provides new insights into the evolution of the Old World monkeys and the early anthropoids.

The Victoriapithecus cranium, designed as KNM-MB 29100, was recovered on Maboko Island, an island in Lake Victoria, Kenya. The site is dated to between 16 and 14.8 million B.P. The skull, thought to be that of male, is estimated to have weighed about 4.3 kilograms.

The researchers conclude on the basis of the anatomy of the cranium and dentition that the new find is clearly an Old World monkey (Cercopithecoidea) belonging to the family Victoriapithecidae, and not to the living family, Cercopithecidae. Details of the anatomy suggest that Victoriapithecus was a frugavore.

Because they are shared by Victoriapithecus, Aegyptopithecus (family Propliopithecidae), and several Miocene hominoids, several characteristics might be primitive features of all Old World anthropoids. Among the traits are a low cranial vault, a well-developed sagittal crest, tall and narrow orbits, and a moderately long snout.

Source: B. R. Benefit and M. L. McCrossin, "Earliest Known Old World Monkey Skull," Nature, 388 (July 24, 1997), 368-371.

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OLDEST HUNTING WEAPONS REPORTED

See Physical Anthropology, 6th edition, Chapter 17, page 457-463; Physical Anthropology: The Core, 2nd edition, Chapter 12, pages 310-321.

"All hominids were hunters and gatherers before the domestication of plants and animals some 13,000 to 10,000 years ago." Students heard this statement up until about fifteen years ago. In more recent years, the idea that early hominids were scavengers and gatherers rather than calculating hunters became predominant. In this scheme, systematic hunting is thought to be relatively recent, perhaps beginning no more recently that 100,000 years ago. This idea springs from the lack of evidence of hunting tools such as spears from early periods of hominid evolution. Data from studies using the scanning electron microscope show that many animals butchered by early hominids were first killed by carnivores.

Now, a new find from a coal mine in Schöningen, Germany, may reverse the thinking about systematic hunting back again to the idea of an earlier date. Three well-preserved spears, as much as 400,000 years old, were found at Schöningen. They are between 6 and 7 feet long and they are shaped like modern javelins. The spears were found in association with stone artifacts and the butchered remains of horses.

Until the find at Schöningen was made, the oldest possible spear was a wooden shaft found inside an elephant skeleton. This shaft, also from Germany, is dated at only 125,000 years ago. It may not have been a spear, but simply a stick used somewhat like a lance.

No hominid bones have been discovered at Schöningen. However, hominid remains have been made in association with butchered animals at Boxgrove, England. The Boxgrove site is dated at about 500,000 B.P. Since there are no hominid bones at Schöningen, the species of hominid that made the spears cannot be determined. Mark B. Roberts, director of the project, says that he would not be surprised to see hunting weapons at Boxgrove. Perhaps hominids were systematically hunting as far back as half a million years ago.

Source: H. Thieme, "Lower Paleolithic Hunting Spears from Germany," Nature, 385 (February 27, 1997), 807-810.

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"MITOCHONDRIAL ROVER"

See Physical Anthropology, 6th edition, Chapter 19, page 507-508; Physical Anthropology: The Core, 2nd edition, Chapter 13, page 343.

In 1987, "Mitochondrial Eve" entered the evolutionary debate over modern human origins. "Mitochondrial Eve" refers to a woman (or a population of women) who lived about 200,000 years ago in Africa and was the ancestor of all modern humans. "Mitochondrial Eve" was proposed on the basis of genetic comparisons of mitochondrial DNA (mtDNA) in living populations. The researchers calculated the length of time needed to establish the variation that is seen in the mtDNA of contemporary human populations. The time estimates of the separation from a common ancestor was based on a molecular clock, built upon the supposed mutation rates that occurred in mtDNA.

In the mid-1980's, the idea that modern humans existed as far back as 300,000 years ago seemed ridiculous to many physical anthropologists. There was no fossil evidence of this and the calculation of mutation rates was a tenuous task at best. However, in the 1990's, fossil evidence for the existence of modern humans has been pushed back from the 40,000 year old date of the mid-1980's to the 130,000 years ago or earlier date of the mid-1990's. This has made the "Mitochondrial Eve" hypothesis seem more plausible.

Now a similar claim has been made by researchers studying the mitochondria of dogs. It has been thought for many years that dogs were domesticated about 14,000 to 13,000 years ago, a time period that corresponds with the end of the last Ice Age. The dogs were thought to have been domesticated to help humans hunt for game that was diminishing in number and variety as the Ice-Age grasslands were replaced by forests. Many herd-dwelling herbivores of the Ice Ages had become extinct or had decreased in numbers by 14,000 B.P. The dogs' excellent sense of smell might have helped humans find elusive prey in the forests.

The new study confirms that dogs were domesticated strictly from wolves with no genes from other members of the family that includes wolves and dogs. The controversial part of the study claims that wolves were first domesticated into what we call "dogs" over 100,000 years ago. This date was arrived at by comparing mtDNA from 162 wolves from 27 localities and 140 dogs representing 67 breeds. The investigators calculated that on the basis of proposed mutation rates, domestic dogs could have separated from their wild wolf ancestors as much 135,000 years ago.

This report has not received wide support. There is no archaeological evidence of the dog cohabiting with humans before about 14,000 years ago, although early dogs may have been anatomically too close to wolves to distinguish them from each other. Even those who have proposed this early date for the domestication of the dog say that the age estimate may be considerably off. However, if people were making hunting weapons much earlier than thought (see the Update article "Oldest Hunting Weapons Reported") and had domesticated the dog about ten times earlier than thought, we will have to revise our ideas on the evolution of hunting and other aspects of hominid social evolution.

Source: C. Vila, et al., "Multiple and Ancient Origins of the Domestic Dog," Science, (June 13, 1997), 1687-1689; V. Morrel, "The Origin of Dogs: Running with the Wolves," Science (June 13, 1997), 1647-1648.

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ORIGINS OF DOMESTICATION IN THE NEW WORLD

See Physical Anthropology, 6th edition, Chapter 19, page 505-511; Physical Anthropology: The Core, 2nd edition, Chapter 13, pages 339-345.

The origins of domestication have always been thought to have been much earlier in the Old World than in the New World. In recent years, Old World plant domestication has been placed at about 10,300 years ago. Plant domestication in the New World has been thought to have begun between 5000 and 3500 years ago.

New studies using an improved radiocarbon dating technique, called accelerator mass spectrometry, has provided a date for squash seeds and stems as early as 10,000 B.P. These squash parts, from a cave at Oaxaca, Mexico, show signs of domestication, such as thicker stems than are found in wild squash.

If the antiquity of this sample is correct, then domestication in the New World started thousands of years before the date currently accepted, and at about the same time as domestication began in the Old World. Yet there is little evidence that any plants other than squash were domesticated at this time; beans and maize were domesticated much later. Perhaps the transition between hunting and gathering and farming in the New World was much longer than in the Old World. In the latter areas, farming was in full swing within 2800 to 1200 years after initial domestication. Of course the long delay between initial domestication and full-scale farming in the New World may be simply due to a lack of evidence.

Source: B. D. Smith, "The Initial Domestication of Cucurbita pepo in the Americans 10,000 Years Ago, Science, 276 (May 9, 1997), 932-934; W. Roush, "Squash Seeds Yield New View of Early American Farming," Science, 276 (May 9, 1997), 894-895.

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