Year 10, General Science

3.4 Human EvolutionFossils support the theory that humans evolved from a common beginning just like all the other animals on Earth. Not everyone agrees with this theory. There is ongoing debate between scientists and those who believe that humans have not evolved but were created by a god or gods.

Primates

Humans belong to the order Primates and have the same features as others in the primate group. Primates have:

forward-facing eyes

five fingers or toes on each limb

four upper and four lower incisor teeth

opposable thumbs (for grasping things)

nails (not claws) on the fingers and toes

large brains for their body size

a flexible skeleton, with arms that rotate in the shoulder socket to allow them to reach behind their body.

Fossil evidence suggests that primates arose from tree-dwelling, shrew-like insectivores around 50 million years ago. This group soon split into several divergent lines of evolution, giving rise to the modern day primates. These are the prosimians (pre-monkeys, similar to lemurs), New World monkeys, Old World monkeys and hominoids.

Evolution of humans

The most recently evolved group of primates is called the hominoids. The hominoids include the lesser apes (gibbons), great apes (gorillas, chimpanzees and orang-utans) and humans. The earliest humans almost certainly arose from the same common ancestor as the other hominoids. Although they have similar ancestors, apes and humans are very distantly related, taking different evolutionary pathways millions of years ago.

Relatively few human fossils have been found, and the human evolutionary process is not definitely known. There is no accurate record of when modern humans emerged, and the exact relationships linking the few existing fossil remains to today’s humans are controversial.

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Year 10, General Science

Our distant relatives

The picture we have of the common ancestor of modern apes and humans is largely based on the fossils of Dryopithecus, an ape-like animal, which first appeared 25 million years ago. Ramapithecus, another ape-like animal, appeared 14 to 16 million years ago, lasting another 6 million years. Some believe Ramapithecus to be the ancestors of the Asian orang-utan, while others see a relationship to other apes and humans. There are significant gaps in the fossil records of 5 to 8 million years ago.

Southern ape

Although apes and humans had similar ancestors in the past, the Homo line diverged from the apes. The first true ‘human-like’ fossils belong to the genus Australopithecus (meaning ‘southern ape’, after the first fossils found in South Africa). The oldest known fossils, Australopithecus afarensis (A. afarensis), are around 4 to 5

million years old. These bipedal (walked on two legs) and had a brain size of 400 cm3, less than one-third that of modern humans (approximately 1450 cm3). All fossils of Australopithecus have been found in Africa.

More recent ancestors

The first clear representation of the Homo line is Homo habilis (handy man). Fossils aged 1.5 to 2 million years old found in East Africa reveal major changesin anatomy (a brain 50 per cent larger) and behaviour (they used tools) from Australopithecus afarensis.

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Year 10, General Science

Homo erectus (upright man) came next. Although fossils have been found in Europe, China and Africa, Homo erectus is often called Java man, after the initial discovery site. The oldest are 1.5 million years old. Average brain size was 1000 cm3.

Other fossil humans

There are other species of the Homo line that have been identified.

Homo neanderthalensis (Neanderthal man) is thought to have lived approximately 35000 to 100000 years ago. Neanderthals are thought to have become extinct due to a change in climate or through competition with other human species in Europe. The common ancestor of humans and Neanderthals probably lived in Europe around 600000 years ago.

Cro-Magnons lived about 10000 to 40000 years ago in Europe and were nomadic hunter-gatherers. They were anatomically similar to modern human, but more robust. The exact reasons for their extinction are not known.

Anatomical changes

Whatever the exact pathways were in the evolution from ape-like ancestor to modern human or Homo sapiens, some changes are clear:

the various forms walked more upright than their ancestors

they developed smaller teeth, reduced eyebrow ridges, shorter arms, flatter feet and non-opposable big toes

they developed flatter faces and a progressively larger brain size.

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Cultural evolution

Humans have changed in many non-physicalways. We have learned how to use tools, and have developed speech, forms of writing, artistic creativity, reasoning powers and a sense of right and wrong. It is these changes that most distinguish modern humans from their ancestors. Humans have highly complex social structures and an accumulation of learning and knowledge. This stored experience is passed from generation to generation, and affects our survival. This is cultural evolution.

It is estimated that of all the animal species that have ever existed, only 1 per cent are alive now. The ultimate fate of most species appears to be extinction. Homo habilis lasted for around 1 million years, Homo erectus around 1.5 million. Modern humans have existed for about 200000 years. With cultural evolution, humans continue to acquire knowledge, enabling us to exert more control over our environment than any other species ever has, but we have probably done more damage also. What does this mean for the future of Homo sapiens?

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Questions

Primates

Question 1. List the characteristics of primates.

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Question 2. What is the importance of a 50-million-year-old shrew-like insectivore to us?

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Question 3. Various features distinguish humans from the other primates. Give two examples each of distinguishing features that are:

a physical

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b non-physical.

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Evolution of humans

Question 4. Give five examples of hominoids.

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Question 5. What distinguishes hominoids from the rest of the primates?

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Question 6. Identify three physical changes marking the evolution of humans from an ape-like ancestor.

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Cultural evolution

Question 7. What is meant by ‘cultural evolution’?

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Question 8. Give two examples of cultural evolution in action.

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Question 9. Place the following primates in correct order of evolution.

Old World monkeys apes humans prosimians New World monkeys

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Question 10. Place the skulls shown in the order of likely evolution. Explain your order.

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