Friday, December 07, 2007

Human Evolution On Trial - The First Humans - Terry Toohill


The First Humans



Of course Human Evolution is impossible until we have humans. Unfortunately, even with all the evidence available, it is impossible to decide when we first became human. Or even what the defining change was. We certainly can’t use technology to identify our ancestors (D’Errico 2003). On this subject Chris Stringer and Robin McKie (1996), very strong supporters of the single origin theory, admit “Nevertheless, archaeologists can find virtually no dissimilarity in types of tools used by Neanderthals or Homo sapiens in the Levant at the time” (about 100,000 years ago). Debate over whether Neanderthals are the same species as modern humans goes back to when their fossil remains were first found around Darwin’s time (Tattersall and Schwartz 2000).



Supporters of the single origin theory believe the defining change is related somehow to the appearance of a single woman, “mtEve”. Her descendants are said to have moved out of Africa at some time and replaced all other humans. But if we decide to use this definition we find for a start that it is actually impossible to identify her descendants and only her descendants in the fossil record. Fossils classified by one worker as being “early modern human” are sometimes considered by other workers not to be (Stringer and McKie 1996). Even the change within Africa is not simple. And when we examine the dating of mtEve we see that her lifetime doesn’t really correspond to any sudden change in human fossils. Besides can we say mtEve’s parents were not human? Or even that mtEve was? Whether she was or wasn’t human we can certainly presume she looked and behaved very much like her brothers, sisters, parents, cousins and neighbours.



Many people like to believe possession of culture is the main thing that separates us from both our earlier ancestors and other animals but it too presumably developed gradually. Our large brain is usually associated with the development of language, culture, abstract thought and a belief in a god or gods and any one of these could be regarded as a defining characteristic. But we don’t know what early humans thought or when they first thought it. Besides any physical measurement we decide on to define the size of brain that makes us human would automatically include the Neanderthals in our definition, and many people would prefer to exclude them. Anyway Cavalli-Sforza (1995) says, “in modern human populations brain volume has little relation to actual intelligence”.



The enlarged brain of modern humans is just one of the many things that make us human and allow us to believe we are superior to the rest of nature. At times it has been fashionable to emphasise upright walking; at other times such things as tool making, shape of teeth, jaws or chin, and possession of language have been considered our defining characteristic (Tattersall and Schwartz 2000).



Any characteristic used to define what makes us human depends on what values are accepted as important by the person making the judgment. His or her attitude depends to a large extent on their own background and what values are believed to be important in their society at the time. K. R. Howe (2003) has examined this phenomenon in relation to the development of ideas about the settlement of New Zealand but his observations have a much wider relevance.



There is actually no sudden change we can use to define the first humans or to date their subsequent migration round the human star, nothing we can use to define our point of origin (Tattersall and Schwartz 2000). All human characteristics seem to have developed gradually (Johanson and Edey 1982) and so it is fairly arbitrary what we actually decide to use as a single defining characteristic for the first humans.



The biggest jump in our evolution was actually the change from Australopithecus to Homo erectus. Homo erectus itself may or may not have evolved from Homo habilis but as you saw in “The First Point” they almost certainly evolved from some member of the Australopithecus group. Apart from by evolution-deniers, Homo erectus is almost universally considered to be a direct ancestor of modern humans, Homo sapiens, if not actually human itself. For convenience we’ll go way back to this species’ development as the beginning. Walker and Shipman (1996) have called Homo erectus an animal in a human body and they give a great account of this species in their publication “The Wisdom of the Bones”.



Homo erectus



Homo erectus appeared in Africa nearly two million years ago, about the time the ice age began. A time of 1,700,000 years is generally accepted although dating in Southeast Asia suggests Homo erectus developed a bit earlier than this (Curtis, Swisher and Lewin 2001). Homo erectus had a primitive stone technology but some members of this species were presumably responsible during the Lower Palaeolithic for the change from the Oldowan to Acheulean.



This early Homo erectus population was about the same height as modern humans, and looked a fair bit like us, except for being stockier and having a smaller brain, a receding or flattened forehead, and a bulging brow ridge. In spite of what artists’ impressions usually show, my feeling is that the modern human hair pattern was already fairly well developed. I have two reasons for thinking this. Firstly the young of most apes, and virtually all monkeys, grab their mother’s hair with their fingers and their toes.

Homo erectus was already walking fully upright, and so a baby’s toes had probably become inadequate for gripping its mother’s hair. Human babies today have a very strong handgrip and many of them like to grab adults' head hair. This would have been the most effective way for an adult to carry a baby and leave its own hands relatively free. Secondly, the lack of human body hair is supposed to have developed to allow efficient heat loss through sweating under tropical conditions (Stringer and McKie 1996). If this is so it would have already developed in the tropical element of our Australopithecus ancestors.



Most people believe Homo erectus was not as good at hunting as we later became but it is agreed they ate more meat than did the earlier Homo habilis or any Australopithecus species (Tudge 1996). Of course even chimpanzees and baboons eat meat when they can get it. Their preferred environment was probably what is called “savannah”. That’s open grassland with small clumps of trees scattered through it, “mosaic vegetation”. In fact this has probably been the preferred human habitat for all our history. Even today. Many people believe it was the decrease in the size of the forest clumps that pushed the development of Homo erectus from its ancestors in the first place.



All the same it actually pays to remember what Homo erectus didn’t have. Our ancestors didn’t have electricity for instance, or clothes, or digital watches, or play the guitar. They presumably didn’t have a very advanced language, if they had one at all. They did use stone for tools and may have used sticks and bones. Everything else we have has been developed since that time.



The grassy plains would also have been different in those days. Humans are not the only creatures to have changed in the last two million years. For example,lions seem to have started developing about that time. This could lead to other interesting theories about the development of extra hair on the head of male animals on the open plains. My guess is the ability to identify male and female from a distance is involved.



We could therefore say Adam and Eve were Homo erectus. You can even get four rivers running from the “Garden of Eden.” Three of them are easy: the Nile, the Congo and the Zambezi. The fourth can be got by splitting the Nile into the Blue and White Niles or by including the Niger River or the Limpopo in a wider “Garden of Eden.” Myth is always flexible. Besides the geography of Africa has changed a bit in two million years. For example the area of Lake Chad may have drained westward into the Niger River. And the Red Sea has probably widened a little.



Expansion



Once a creature can move into an area previously unoccupied by anything like its own species expansion can be quite rapid. The fox for example was introduced to Victoria in the south east of Australia and within sixty years it had reached the Kimberly coast, over 3000 kilometres to the northwest (Flood 1988). Humans don’t breed as fast as foxes but their spread would also be very rapid when they are able to move into previously uninhabited areas. They live off the easy pickings first.



Homo erectus had managed to reach their maximum spread through Europe and Asia by at least 800,000 years ago but, because of the extreme cold, couldn’t get north of about latitude 40° or 50° north and so they failed to get to America. They weren’t able to cross the water to Australia either but if we use mainland Southeast Asia to represent the Australian point they or their immediate descendants did occupy the five main points on the human star.



The geographic extremities of a population are the most different. As Homo erectus spread out selection in different regions of the world led to change in the various populations’ characteristics and the development of a series of clines. In Homo erectus times the Indonesian island of Java was occasionally connected to mainland Southeast Asia. In fact Java was then at the very extreme end of what I have called the human star’s Australian point. An accident of history has meant the type specimen of Homo erectus is represented by its first discovery in Java (Jobling et al 2004). This specimen and others in the region had an especially large brow ridge. Within Southeast Asia Homo erectus remained fairly isolated and changed very little over the period between at least 1,500,000 years ago until probably as recently as 40,000 years ago, or even more recently (Tattersall and Schwartz 2000, Wade 2001 and Curtis, Swisher and Lewin 2001).



The name Homo ergaster is sometimes used these days as a replacement for Homo erectus outside of Southeast Asia but I’ll carry on using Homo erectus for them all. I feel sure they are no more than subspecies rather than being separate species anyway.



Subspecies?



No Homo erectus fossils have yet been found in the Northwest European point of the star although stone technologies usually associated with them have been. The earliest substantial remains found so far are of a species that has been called Homo heidelbergensis, although a species Homo antecessor dated at 750,000 years has been named from fragments. The first humans to reach Europe were presumably members of one or other of these species. In that point of the star they eventually developed into the Neanderthals (Homo neanderthalensis). In the East Asian point of the star Homo erectus developed into what has been called “Peking Man” (Homo pekinensis) and in the African points later Homo erectus are called “Rhodesian Man” (Homo rhodesiensis). All these species may also have had early input and gene flow from another species, Homo heidelbergensis, though.



I have given names of some different species on the human line but a few lumpers believe humans have consisted of a single continually evolving species since Homo erectus evolved (Milford Wolpoff quoted in Gore 2002). They believe two million years change is insufficient time to lead to separate species. The number of species in the human line may have been exaggerated. We look more closely at the species we are most interested in rather than at other animals. Small differences have been emphasised. There is probably also a desire by many workers to discover a new species. In other words all these first humans should be called Homo sapiens erectus.



Today we are quite a variable and still evolving species, even within a small area let alone over the whole world. Sure, as supporters of the single origin theory point out, our distant ancestors are very different from us (Stringer and McKie 1996). The greatest variations within any species always appear when we compare the opposite extremities of space and time. But the variations over time or space are actually fairly gradual.



Precise boundaries between the various human species are impossible to define through both time and space. Different workers often classify the same fossil as being a different species. It seems to me classifications of such species as Homo erectus, Homo heidelbergensis, “Archaic Homo sapiens” and even the much earlier Homo habilis have often been made according to both when and where it is considered to have lived rather than what it actually looked like. This is really a circular means of classification. It shows that all human species were quite variable and there is not straightforward progress from one species to another. I have already pointed out several times that different species can breed together in the right circumstances. Therefore it is sort of irrelevant whether we class all these humans as separate species or not. Giving them different names does allow us to look more closely at details of human development though.



Anyway, even outside Africa Homo erectus began changing towards Archaic Homo sapiens over a wide area (Stringer and McKie 1996). Development was by gradual change rather than by sudden jumps. This could only have happened by gene flow. Population isolation leads to diversification, not change in a single direction.


see also :: 'Species Or Not'





References





Cavalli-Sforza, Luigi Luca and Cavalli-Sforza, Francesco (1995) The Great Human Diasporas. Addison- Wesley

Curtis, Garniss, Swisher, Carl and Lewin, Roger (2001) Java Man. Little, Brown and Company, London.

D’Errico, F. (2003) The Invisible Frontier: a Multiple species Model for the Origin of Behavioral Modernity. (pdf)Evol. Anthrop.12, 188[-202.

Flood, Josephine (1988) Archaeology of the Dreamtime. Collins, Australia.

Gore, Rick (2002) New Find. National Geographic, Vol. 202, No. 2 August

Howe, K. R. (2003) The Quest for Origins. Penguin, New Zealand

Jobling et al (2004) Human Evolutionary Genetics. Garland Science, New York.

Johanson, Donald and Edey, Maitland (1982) Lucy. Warner Books, New York.

Stringer, Christopher and McKie, Robin (1996) African Exodus. Random House, UK.

Tattersall, Ian and Schartz, Jeffrey H. (2000) Extinct Humans. Westview Press, New York.

Tudge, Colin (1996) The Time Before History. Scribner, New York.

Wade, Nicholas ed. (2001) The New York Times Book of Fossils and Evolution. The Lyon Press, New York.

Walker, Alan and Shipman, Pat (1996) The Wisdom of the Bones. Alfred A. Knopf, New York.



1 comment:

terryt said...

Link to the next step in the argument:

http://remotecentral.blogspot.com/search/label/Human%20Evolution%20On%20Trial%20-%20Species%20or%20Not

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