Human Evolution

Topics covered on this page are:

Introduction
Features of Primates
We started in Africa
Migration
Cultural Evolution
Human intervention in the process of selection.

Introduction

The mechanisms that led to the evolution of the huge diversity of species living today are believed to be identical to those that led to the evolution of our own species (Homo sapiens).

Whilst the above is true in general, there are details of the evolution of humans which are still the subject of much research and sometimes much controversy.

It is generally accepted that humans share a common ancestor with the other primates, and many lines of evidence support this. Most textbooks will have a diagram showing the most likely relationships between primates. Some of the animals on this diagram survive today, others have long been extinct.

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Features of Primates

Look at the pictures of primates here, look at other primate pictures in your textbook, visit the Primate Gallery Web site, or best of all, take a trip to the Zoo and look at the primates there.

You will see that all of these animals (including our own species), share many common structural, functional and behavioural characteristics, that is, there are many similarities in our phenotypes, including:

Rounded faces with reduced snouts. Eyes protected by bony ridges.
Relatively large brains, with a small area for smell, a larger area for vision.
Large eyes point forward, giving binocular 3D vision. Colour vision present.
Variation in tooth size and shape. A varied, omnivorous, diet is possible.
Collarbones present, enabling brachiation (swinging by arms).
Mobile limb joints, giving a wide range of limb movement.
Five digits on hands and feet. Nails, not claws. Opposable thumbs enable grasping.
Many quadrapedal, but most sit upright. Some bipedal, freeing hands for other activity.
Internal fertilisation, long gestation. Long period of parental care.
Social groups usually well developed. Heirarchies common. Communication evident.

This seems too much of a coincidence to blame on convergent evolution. When the biochemical evidence, based on similarity of DNA sequence for selected, common genes, is examined, it is clear that all of these animals are closely related.

Does this similarity between ourselves and our primate relatives mean that we came from "monkeys", or that "monkeys" evolved from humans?

Certainly not!

This is merely another example of divergent evolution from a common ancestor. Somewhere back in evolutionary history the first primate ancestor appeared. Then, over time, mutations occurred in some populations of that animal, natural selection acted to favour the best adapted individuals for the particular environments, and slowly new species evolved. This evolution continued and the 'branches' of the primate tree sprouted. Some branches flourished, some died, but what we are left with is a variety of similar but significantly different species. All are primates, all came from that common ancestor, but they are each the products of the environments that shaped their present forms.

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We started in Africa

At least 4 million years ago the first hominid ancestor appears in the fossil record in Africa.

Family Hominidae are humans and their (now extinct) close relatives. As the hominids evolved, many phenotypic changes were observed:

Body size varied, with a tendency to an increase over time.
Some species had thick, robust skeletons, others were gracile, or fine boned.
Skull capacity, and presumably, brain volume increased.
Skull bones and teeth had proportions more like apes than like modern humans.
But pelvis and thigh bones indicated that they walked on two feet (bipedal gait).
With increasing brain size it seems that the ability to make and use tools slowly developed.

Eventually one species of hominid remained. Perhaps Homo sapiens was better adapted to survive a major environmental change. Perhaps 'he' was merely smarter and he directly or indirectly caused the extinction of other Homo species which were already beginning to migrate out of Africa. Back to the top of this page

Migration

The evidence does seem strong that the origin of our species is somewhere in Africa, but the details will probably never be known for sure.

However, there is a great deal of evidence to show that many groups of early Homo sapiens migrated out of Africa about 200 000 years ago. The pressures of selection and adaptation that have been described for other species have acted on these population founding groups over the succeeding years and produced the sub-groups of the human species that we know as races.

Since interbreeding between members of different human races can and does occur, these groups must still be classified, according to the rules of taxonomy, as members of the same species.

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Cultural Evolution

Early Hominids developed a unique phenotype. The combination of structural features and enlarged brain enabled Hominids to manipulate their environment in a way no other animal has been able to do.

Over hundreds of thousands of years, Hominids, and later members of the Genus Homo, gradually learned how to live and survive in a variety of environments. Major milestones in this journey from Hominid to modern man (Homo sapiens) have included:

2.0 - 1.5 mya: Homo habilis, in E. Africa has permanent dwelling places, makes stone tools.
1.7 mya - 200 000 BP: H. erectus, in Africa, Asia and Europe, migrates out of Africa, uses fire.
90 000 - 30 000 BP: H. sapiens neanderthalis, in Europe, Africa and W. Asia, practise ceremonial burial.
30 000 BP to present: H. sapiens sapiens, world wide, use bone needles, produce art forms, perhaps begin their own decline by irreversible habitat destruction...?

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Human Intervention in the Process of Selection

For many years, humans have been manipulating the process of evolution to suit their own ends. By choosing organisms with desired phenotypes as breeding stock, humans are practicing artificial selection.

There is value in this practice when desirable characteristics such as disease resistance in crop plants is achieved. But sometimes undesirable results are obtained, such is the case with the development of antibiotic resistance in some pathogenic organisms.

As a result of human activity, rapid environmental changes have occurred in some locations. These, in turn, have changed ecosystems and habitats. As we have discussed earlier, mutations occur very slowly and are not necessarily favourable. It is, therefore, not surprising that many species are now endangered and many others have recently become extinct.

Recent advances in medical technology have reduced the incidence of death from human genetic disease, with affected individuals now remaining in the population long enough to reproduce. The implications for the frequency of the "disease" alleles in population gene pools should be obvious - they would be expected to increase. This may not seem to be a problem if the affected individuals can be treated, but the cost of such treatment may eventually place economic burdens on families and communities. Such issues will need to be addressed.

We welcome your comments about this project.

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This page is maintained by Jenny Herington, who can be contacted at bio_cat@bioserve.latrobe.edu.au by email. All of the pages at the VCE Biology Students' site are copyright © Biochemistry, LaTrobe University. Last update : 12 September 97

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