Evolution and our human origins

-Daphna Whitmore

Eighty years ago Tennessee school teacher John Scopes was put on trial for teaching evolution. He was duly found guilty, but the verdict was later overturned on a technicality. Anti-evolutionists in the United States are still at war with science. In November 2005 a court ruled in Kansas that science teachers must cast doubt on evolution and present “Intelligent Design” as an alternative theory. More significantly on 20 December 2005 a Pennsylvania court ruled that intelligent design could not be taught in public schools in that state. The ruling was a significant setback for ID and a victory for science and rational thought.

Even though Darwin’s Origin of the Species was published 150 years ago many people lack even a rudimentary understand of evolution. A Gallup poll a few yars ago in the United States found that over 40 per cent of people agreed with the statement “God created human beings pretty much in their present form at one time within the last 10,000 years or so.” Only 12 per cent “agreed humans have developed over millions of years from less advanced forms of life, and God had no part in this process”. [1]

Public ignorance is one thing, but just as worrying is the lack of evolutionary thinking in modern medical science. In the medical profession an understanding and application of evolutionary principles is rare. This, despite evolution being one of the most solidly proven scientific theories. [2]

Evolution

Mention evolution and the name Charles Darwin immediately springs to mind, but the notion was around well before Darwin. By the middle of the eighteenth century ideas about organic evolution and the transformation of animals were gaining acceptance. In the early nineteenth century Lamarck had published a theory of evolution and the geologist Charles Lyell was interpreting the earth’s history as a process of gradual change.

Darwin formulated his theory of natural selection after working as a ship’s naturalist on board the HMS Beagle. Perhaps wanting to avoid controversy he decided to keep quiet about his groundbreaking explanation of how evolution worked and locked his manuscripts away in 1844. There they might have stayed until he died if it was not for Alfred Wallace who, in 1858, independently discovered natural selection. Darwin was hurriedly forced to reveal his findings and the two agreed to present their papers on the same occasion to the Linnean Society.

Darwin’s theory held that the rich variety of life was a result of the existence of a diverse set of environments to which different species have become fitted by natural selection. The process he called adaptation. [3]

Life’s persistent pulse

Life developed on earth very early on. The earth’s surface became solid 3.9 billion years ago but within a short time - around 3.85 billion years ago - in a primordial chemical soup, life first appeared. Nothing grand, just single cell replication, but it was life. Life has not stopped since, although 99.99 per cent of all species that have ever existed are extinct, a fate that awaits nearly all species.

Life evolved in the sea and there it remained for most of earth’s history. It is thought the first cells must have been anaerobic because there was no oxygen in the atmosphere. Photosynthesis evolved around 3.4 billion years ago and gradually transformed the earth’s atmosphere into about 20 per cent oxygen. Bacteria oxidised the world, one-celled organisms invented sexual reproduction and complex life evolved.

All life is interrelated and from the seas it ventured out on to land and into the air.

Mammals, the broad group that humans belong to, originated hundreds of millions of years ago, from reptilian animals. By around 65 million years ago, when dinosaurs had become extinct, some mammals had evolved into the earliest primates. These later gave rise to monkeys, apes, and humans. The fossil evidence in Africa suggests the appearance around 20 million years ago of the first hominoids - the family which includes all living and extinct humans and apes. Human and ape ancestors branched off in separate directions around seven million years ago.

A giant step

The first hominins (the collective term for all human-related species, or hominids as they were formerly categorised) were apelike creatures that had moved from the tropical forests of Africa to the open savannas and adopted upright walking. They were australopithecines of which there were many varieties. They were not direct ancestors of ours, more of a side branch that died out.

The picture that has emerged of the human family tree is of a diverse bush not a single ascending line.

The homo genus is thought to have started with Homo habilis (handy man) and ended up with Homo sapiens (the thinker). Along the way there were other branches: Homo ergaster, Homo neanderthalensis, Homo rudolfensis, Homo heidelbergensis, Homo erectus, Homo antecessor, and Homo floresiensis whose fossil remains were recently discovered on the Indonesian island of Flores. [4]

H. habilis were bipedal, made tools, had larger brains, smaller teeth, and more prominent noses than apes. They were probably both foragers and scavengers rather than full time hunters.

The human brain has lopsided architecture with left and right dealing with different functions. This division of mental labour makes most humans right-handed and about one-fifth left handed. No other primates have this specialisation but H. habilis did. With a brain about 50 per cent larger than that of australopithecines there may have been room for the feature associated with speech production known as Broca’s area. The tools made by H.habilis stayed unchanged for more than 500,000 years and showed no sign of innovation.[5]

It is not fully understood why human brains became so large. They are demanding organs, making just two per cent of the modern human’s body mass but using 20 per cent of its energy.[6] As meat is a concentrated and nutritious food it is thought to have played an important part in the growth of the brain.

Around 1.5 million years ago H.erectus appeared. They had more versatile tools than H.habilis a much larger brain and a large brow ridge but a smaller face and more prominent nose with downward-facing nostrils. The teeth were small and the lower jaw was still chinless.

H.erectus was tall and long-legged and travelled out of Africa, across Europe and Asia.[5] What was the impetus behind this wandering? It is thought to be food. Meat-eaters generally require far bigger home ranges than do herbivores of comparable size because they have fewer total calories available to them per unit area. With its big build and growing dependence on a meat diet erectus most likely needed much more territory than the smaller, more vegetarian australopithecines.[7]

Labour and language

H. erectus had mastered fire and was able to cook, greatly expanding its food sources. According to paleontologist Richard Leaky it is very likely that erectus used speech as there are signs of a Broca’s area, although there are some who dispute this. Furthermore, the appearance of tool making suggests that some level of speech was necessary.

The connection between the development of upright walking, tool making and language was examined in the 19th century in a brilliant essay by Frederick Engels entitled The Part Played by Labour in the Transition from Ape to Man. Engels looked at the divergence of apes and humans, tracing the transition from knuckle-walking common to apes, to the bipedalism of humans which freed up the hand, bringing major consequences. While monkeys and apes use their hands for a variety of simple functions “no simian hand has ever fashioned even the crudest stone knife” he points out. [8]

Acknowledging that most likely tens of thousands or hundreds of thousands of years were involved in the development of the human hand to attain ever greater dexterity and skill, Engels noted “the hand is not only the organ of labour, it is also the product of labour”.[8] Engels doesn’t treat the hand in isolation but shows how it is one part of a highly complex organism. As the hand developed other parallel developments took place, such as the adaptation of the feet. Darwin had established the law of correlation of growth which explained that particular forms of individual parts of an organic being are always connected to other parts of the organism which have no apparent connection. “Thus all animals that have red blood cells without cell nuclei, and in which the head is attached to the first vertebra by means of a double articulation (condyles), also without exception possess lacteal glands for suckling their young. Similarly, cloven hoofs in mammals are regularly associated with the possession of a multiple stomach for rumination. Changes in certain forms involve changes in the form of other parts of the body, although we cannot explain the connection.”[8]

As the hand, toolmaking and human labour developed so to did the organ of speech. “In short, men in the making arrived at the point where they had something to say to one another”.[8]

With erectus there was the first appearance of hominins outside of Africa, the development of systematic hunting, the first appearance of “home bases”, the first systematic tool making, the use of fire and the first sign of extended childhood. [9]

Apart from areas in Java where erectus became extinct in the last 500,000 years this species made room through evolutionary change or replacement for new species of ‘archaic” homo sapiens.[5] (The discovery of Homo floresiensis, which died out 12,000 years ago due to a volcanic eruption, has raised the possibility that there are other descendant species of Homo erectus yet to be discovered in the islands of South-East Asia. In addition, Homo floresiensis is so different from other members of genus homo that it provides further evidence against linear evolution.)

Recent DNA studies of several populations suggest that modern humans originated in Africa around 170,000 years ago, possibly from erectus/ergaster. Our ancestors migrated to other parts of the world replacing other hominins, including the neanderthals. Although we lived alongside neanderthals there is no genetic evidence of interbreeding, and they gradually became extinct 27,000 years ago.[9]
Around 90,000 years ago humans reached Asia, 50,000 years ago Australia and Europe, and 30,000 years ago arrived in North America via Siberia.

The human race

Despite differences in skin colour and other physical features that were selected for in various geographical latitudes, there is far more genetic variation from individual to individual than there is between different ethnic populations. According to geneticist Richard Lewontin about 85 per cent of variation is among individuals within local national or linguistic populations. Only around 6 to 10 per cent of the total human variation is defined by skin color, hair form, and nose shape and most variation does not show any “race” clustering. [10]

Humans are not alone in this. Lewontin points out that zoologists also abandoned the category of “race” for dividing up groups of animal populations within a species, because so many of these races turned out to be based on only one or two genes, so that two animals born in the same litter could belong to different “races”. [10]

As tempting as it is to think of humans as special - and our intelligence, technology and culture is a defining feature - our existence was a matter of chance not design. A slight variation in conditions and there would have been no evolution of humans.
As geneticist JBS Haldane observed: “If one could conclude as to the nature of the Creator from a study of his creation it would appear that God has a special fondness for stars and beetles”.

……………………………………………………………………..

Notes
1. Holmes, B. and J. Randerson, A sceptic’s guide to intelligent design. New Scientist, 2005.
2. Since the 1990s the ideas of evolutionary medicine have been developing, but they are still on the fringes. A leading figure in this field is the evolutionary biologist Paul Ewald.
3. There is not the space in this article to delve into the various debates among evolutionists, but a brief mention is warranted of the further development of evolutionary theory by geneticist and biologist Richard Lewontin. He argues that organisms don’t “adapt” to an externally imposed environment rather they construct it. “The world inhabited by living organisms is constantly being changed and reconstructed by the activities of all of those organisms, not just by human activity.” In his book The Triple Helix he contends that construction is a more suitable concept than adaptation.
4. The word homo is Latin for “person”, chosen originally by Carolus Linnaeus in his classification system. The word “human” is from humanus, the adjectival form of homo.
5. Andrews, P. and C. Stringer, The Book of Life. The Primates’ Progress, ed. S.J. Gould. 1993.
6. Bryson, B., A Short History of Nearly Everything. 2003.
7. Leonard, W.R., Dietary change was a driving force in human evolution. Scientific American, 2002.
8. Engels, F., The Part Played by Labour in the Transition from Ape to Man. 1876.
9. Lewin, R., Human Evolution. 1998. 10. Lewontin, R., Confusions About Human Races. 2005.

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