13 Emergence of Man

Dr. Arpita Mandal

Contents of this unit

1. Introduction

2. The debate on the origin

3. Important early modern Homo sapiens sites

4. Who are modern humans?

5. Anatomical features

6. Material culture

7. Origins

8. Explanation of their expansion

9. What mitochondrial DNA reveals?

10. New hypothesis

11. Summary

Learning objectives:

• Who are Humans?
• Where did they come from?
• When did they first appear?
• What was their path of emergence?

Introduction:

All modern human beings belong to the genus Homo. Between 2.5 and 2.3 million years ago, the fossil record reveals the emergence of several new hominid species that anthropologists place into the genera Paranthropus and Homo. Both genera most likely have evolved from a late species of Australopithecus.

Genus Homo evolved some 400,000 years ago. This is known from the fossil evidence of a lower jaw found in Africa. The time dates approximately to 2.8 million year when it is learned that Homo branched out from a common ape-like ancestor.

The early fossils belonging to the genus Homo were originally placed into a single species, Homo habilis (handy human being). The first specimen of H.habilis was discovered by Louis and Mary Leakey in 1960 at Olduvai Gorge.

  This lower jaw found in the Afar region of Africa show features common to both the Australopithecus and Homo. The sloping chin was somewhat similar to Australopithecus while narrow and symmetrical molars push it towards the genus, Homo. Two early modern hominids from Israel, one from Jebel Qafzeh and the other from Tabun, placed anatomically modern humans well back into the Neanderthal time range, the dating being between 115,000 and 96,000B.P. and 100,000 B.P years respectively. Early modern humans are often seen in terms of a population called Cro-Magnon, which lived about 28,000 years ago or later. In 1868, several partial skeletons were discovered in a rock shelter in south-western France. They became the prototype of Homo sapiens. A recent discovery of a skull at a site near the village of Buia, Eritrea, East Africa shows a mixture of Homo erectus and Homo sapiens features at around one million years ago.

  The past century and a half of palaeoanthropological discoveries have provided a general outline of hominid evolution. At around 1.9 million years ago a new grade of hominids, Homo ergaster and Homo erectus begin to appear. Many fossil hominids dating from about one million to 130,000 years ago show more Homo sapiens like characteristics than Homo erectus like, these are placed into the species Homo heidelbergensis. However populations of Parathropus survived until about 900,000 years B.P.; some populations of Homo erectus survived as late as 27,000 years B.P.

  The Neanderthals existed between 130,000 to about 30,000 years ago. They have been seen as a direct ancestor to modern Europeans and a side branch of humanity that genetically contributed little or nothing to modern populations. Today details of Neanderthal anatomy such as an oval shaped foramen magnum, the distinctive structure of th middle and inner ear, and the unique shape of the nasal region have convinced paleoanthropologists that Neanderthals should be placed in a separate species, Homo sapiens neanderthalensis.

The debate on the origin

• It has been continuining for long now, that H. erectus, considered to be the precursor to modern humans, evolved in Africa and gradually spread or migrated to Europe and Asia about 1.7 million years ago. The dating considered for the appearance of the anatomical modern humans is considered to be at least 130,000 years ago.
• Further, it was commonly agreed upon that, by 100,000 years ago, several species of hominids populated the Earth. The populations of the H. sapiens—us—lived in Africa, whereas the populations of H. erectus in Southeast Asia and China, and Neanderthals in Europe. Then in around 50,000 years ago, there was a sudden explosion of human migration out of Africa and by about 30,000 years ago, only the anatomical modern humans were existing.
• The debate arises by differing definitions and views of the archaic and anatomical modern humans.
• Anatomical humans were supposed to differ from their counterparts by possessing qualities of the brain which helped them to plan ahead, innovate different technological methods, being able to adapt themselves to their environmental situations, exhibiting behavior like, cave painting, bead making or burying the dead.

Important Early Modern Homo sapiens Sites

 Source: http://www.nature.com/scitable/content/map-of-homo-erectus-fossil-localities-96680469

Who are modern humans?

• All over the world people are classified as classified as Homo sapiens. We appeared about 200,000 years ago. Henceforth, our evolution progressed further with the advent of varying technologies. It can be clearly stated modern humans were contemporary with the Neanderthals and did not come after them. . Furthermore, the forehead is also relatively higher. Chin is present only in the modern humans.
• Compared to the Neanderthals and other late archaic humans, modern humans generally have lighter skeletons. Their skulls are more rounded and their brow ridges generally protrude much less. They rarely have the occipital buns found on the back of Neanderthal skulls. They also have relatively high foreheads, smaller faces, and pointed chins.
• The first fossils of early modern humans to be identified were found in 1868 at the 27,000-23,000 year old Cro-Magnon rock shelter site near the village of Les Eyzies in south western France. They were subsequently named the Cro-Magnon people. They were very similar in appearance to modern Europeans. Males were 5 feet 4 inches to 6 feet tall (1.6-1.8 m.) and were 4-12 inches (10-31 cm.) taller than Neanderthals. Their skeletons and musculature generally were less massive than the Neanderthals. The Cro-Magnon had broad, small faces with pointed chins and high foreheads. Their cranial capacities were upto 1590 cm3, which is relatively large even for people today.

Three important shifts in human evolutionary history:

• the emergence of genus Homo
• the transition between non-erectus early Homo and H. erectus, and
• The appearance of regional morphological variation in H. erectus (including Homo ergaster).

Using this integrated data set, we consider the implications for understanding the changing selective pressures that led to the transition to and evolution of early Homo.

Anatomical features

Modern humans have a distinctly round head that contains a large brain that averages 1350 cubic centimeters. From front to back, the cranial arch, or vault, is short but high. The occipital bone is delicate.

Compared with earlier hominids, the modern human’s face and eye sockets are smaller, the front of the upper jaw and the mandible are also small. The modern human has a strong chin, which is the bony projection of the lower part of the mandible. The modern human skeleton is less robust and the musculature is lighter as compared to the earlier hominid skeletons.

Material Culture

The archaeological record provides evidence of several key behaviours—including changes in dietary niche, ranging, and cognition—that are often associated with the rise of genus Homo. The manufacture and use of stone tools have long been thought to signal a foraging shift and to be associated with the origin of Homo. The first unambiguous tools appear at 2.6 Ma, with cut-marked animal bone ubiquitous in sites. However, occurrence of one cut-marked bone has been argued to occur before the emergence of Homo. Although the Oldowan is linked to carcass processing, other uses related to plant or food processing are important. This emerging picture is consistent with dental evidence and supports a modest dietary shift to more carnivory in Homo and increased dietary breadth compared with Australopithecus. A second noteworthy change occurs at approximately 1.95 Ma with an increase in stone transport distances that suggests the movement of rock over ∼12 km interval. Further, by 1.76

Ma, Acheulian tools appeared in the record. These changes are often attributed to H. erectus and are used to suggest increased range, although it is worth noting that this temporal association may be coincidental and that increased transit distances may be characteristic of all post-2.0-Ma Homo.

Origins

Current data suggest that modern humans evolved from archaic humans primarily in East Africa. A 195,000 year old fossil from the Omo 1 site in Ethiopia shows the beginning of the changes in skull that can be associated with modern people, including a rounded skull case and possibly a projecting chin. A 160,000 year old skull from the Herto site in the Middle Awash area of Ethiopia also seems to be at the early stages of this transition. It had the rounded skull case but retained the large brow ridges of archaic humans. Somewhat more advanced transitional forms have been found at Laetoli in Tanzania dating to about 120,000 years ago. By 115,000 years ago, early modern humans had expanded their range to South Africa and into Southwest Asia (Israel) shortly after 100,000 years ago. There is no reliable evidence of modern humans elsewhere in the Old World until 60,000-40,000 years ago, during a short temperate period in the midst of the last ice age.

Explanation of their expansion

Since the early 1980’s, there have been two leading contradictory models that attempt to explain modern human evolution– the replacement model and the regional continuity model.

The replacement model of Christopher Stringer and Peter Andrews proposes that modern humans evolved from archaic humans 200,000-150,000 years ago only in Africa and then some of them migrated into the rest of the Old World replacing all of the Neandertals and other late archaic humans beginning around 60,000-40,000 years ago or somewhat earlier. If this interpretation of the fossil record is correct, all people today share a relatively modern African ancestry. All other lines of humans that had descended from Homo erectus presumably became extinct. From this view, the regional anatomical differences that we now see among humans are recent developments– evolving mostly in the last 40,000 years. This hypothesis is also re ferred to as the “out of Africa”, “Noah’s ark”, and “African replacement” model. (Edwards, 2012). The regional continuity model (or multiregional evolution model) advocated by Milford Wolpoff proposes that modern humans evolved more or less simultaneously in all major regions of the Old World from local archaic humans. Supporters of this model believe that the ultimate common ancestor of all modern people was an early Homo erectus in Africa who lived at least 1.8 million years ago. It is further suggested that since then there was sufficient gene flow between Europe, Africa, and Asia to prevent long-term reproductive isolation and the subsequent evolution of distinct regional species. It is argued that intermittent contact between people of these distant areas would have kept the human line a single species at any one time. However, regional varieties, or subspecies, of humans are expected to have existed (Edwards, 2012).

Use of Mitochondrial DNA

Beginning in the 1980’s, Rebecca Cann, at the University of California, argued that the geographic region in which modern people have lived the longest should have the greatest amount of genetic diversity today. Through comparisons of mitochondrial DNA sequences from living people throughout the world, she concluded that Africa has the greatest genetic diversity and, therefore, must be the homeland of all modern humans. Assuming a specific, constant rate of mutation, she further concluded that the common ancestor of modern people was a woman living about 200,000 years ago in Africa. This supposed predecessor was dubbed “mitochondrial Eve”. More recent genetic research at the University of Chicago and Yale University lends support to the replacement model. It has shown that variations in the DNA of the Y chromosome and chromosome 12 also have the greatest diversity among Africans today. John Relethford and other critics of the replacement model have pointed out that Africa could have had the greatest diversity in DNA simply because there were more people living there during the last several hundred thousand years. This leaves open the possibility that Africa was not necessarily the only homeland of modern humans.

New Hypothesis: Assimilation model

It is apparent that both the complete replacement and the regional continuity models have difficulty accounting for all of the fossil and genetic data. Hence, a new hypothesis knows as the assimilation (partial replacement) model has emerged. It takes a middle ground and incorporates both of the old models. Gunter Brauer, of the University of Hamburg in Germany, proposes that the first modern humans did evolve in Africa, but when they migrated into other regions they did not simply replace existing human populations. Rather, they interbred to a limited degree with late archaic humans resulting in hybrid populations. In Europe, for instance, the first modern humans appear in the archaeological record rather suddenly around 45-40,000 years ago. The abruptness of the appearance of these Cro-Magnon people could be explained by their migrating into the region from Africa via an eastern Mediterranean coastal route. They apparently shared Europe with Neanderthals for another 12,000 years or more. During this long time period, it is argued that interbreeding occurred and that the partially hybridized predominant Cro-Magnon population ultimately became modern Europeans. In 2003, a discovery was made in a Romanian cave named Peştera cu Oase that supports this hypothesis. It was a partial skeleton of a 15-16 year old male Homo sapien who lived about 30,000 years ago or a bit earlier. He had a mix of old and new anatomical features. The skull had characteristics of both modern and archaic humans. This could be explained as the result of interbreeding with Neanderthals according to Erik Trinkaus of Washington University in St. Louis. Alan Templeton, also of Washington University, reported that a computer-based analysis of 10 different human DNA sequences indicate that there has been interbreeding between people living in Asia, Europe, and Africa for at least 600,000 years. This is consistent with the hypothesis that humans expanded again and again out of Africa and that these emigrants interbred with existing populations in Asia and Europe. It is also possible that migrations were not only in one direction–people could have migrated into Africa as well. If interbreeding occurred, it may have been a rare event. This is supported by the fact that most skeletons of Neanderthals and Cro-Magnon people do not show hybrid characteristics

Schematic representation of the emergence of H. sapiens from earlier species of Homo. The horizontal axis represents geographic location; the vertical axis represents time in millions of years ago. Blue areas denote the presence of a certain species at a given time and place. Early modern humans spread from Africa across different regions of the globe and interbred with other descendants of Homo Heidelbergensis, namely Neanderthals, Denisovans, and unknown archaic African hominins (top right).

Summary

• Where fully modern H. sapiens first evolved is still being debated, however, Africa seems to be the origin of this new stage in human evolution about 100,000 years ago or perhaps earlier.
• In various places populations appeared who were basically migratory.
• It is very likely that the rate of evolution for our species has continuously accelerated since the end of the last ice age, roughly 10,000 years ago.
• Our human population has grown drastically, and moved into new kinds of environments, including cities, where we have been subject to new natural selection pressures.
• Humans have been able to adapt to the new environment as it could acquire a greater genetic diversity.
• As populations become large due to this adaptation and increased the types of variations among them, it helped the humans to have a larger gene pool.
• Larger the population more the mutation causing more variation in its gene pool.
• As long as there is differential reproduction among those carrying the variants, natural selection would take its course.
• In this scenario, current human population is poised for significant evolution toward what kind of descendant we do not know.

    The legacy of our human evolutionary past has been one of unparalleled evolutionary success, due to remarkable adaptability born of our expanded brains. The legacy we leave for the future will depend upon how well we choose to adapt to the predicament we have brought upon this world.

References:

• Conroy, G., 2000, Reconstructing Human Origins: A Modern Synthesis. New York: W. W. Norton.
• Edwards S.,2012, Analysis of Two Competing Theories on the Origin of Homo sapiens sapiens: Multiregional Theory vs. the Out of Africa 2 Model, The Collegiate Journal of Anthropology,vol:1
• Ehrlich, Paul, E.,2000, Human Natures, Genes, Cultures, and the Human Prospect. Washington, DC: Island Press for Shearwater Press.
• Howells, W.W., 1976, explaining modern man: Evolutionists versus migrationists, Journal of Human Evolution, vol 5,477-496.
• Pettitt, P (2009 a-i). The rise of modern humans. In: Scaare, C. the Human Past. 2nd ed. London: Thames and Hudson 124-173.
• Wolpoff, M and Thorne, A (1992). ‘The Multi-Regional Evolution of Humans’ Scientific American, 28-33.

Internet links: Accessed on 15.2.15

• http://anthropology.si.edu/HumanOrigins/ha/weid.html
• Becoming Human: Paleo-anthropology, Evolution, and Human Origins. The Institute of Human Origins.<http://www.becominghuman.org>.
• http://anthro.palomar.edu/homo/homo_2.htm
• http://www.nature.com/scitable/content/map-of-homo-erectus-fossil-localities-96680469
• www.theguardian.com