Human Evolution

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Text of Human Evolution

  • 1.We have seen that there is abundant evidence for the common descent of human beings and the rest of the living world.
    In Darwins time very little was known of the steps or intermediate stages that led to us.
    This has changed dramatically in the last 150 years and now we have a wealth of data that enables us to reconstruct much of our origins.

2. Human beings have always pondered over how they came into existence. This has given rise to a wide variety of speculation and several beautiful stories.
The Judeo-Christian tradition has the myth of Adam and Eve and the garden of Eden.
3. In ancient Indian mythology, Brahma created the world. He along with Siva the destroyer and Vishnu the preserver formed the Hindu trinity of Gods.
However, moving beyond mythologies science has pieced together a far more interesting story that is still in the process of development.
4. The scientific history of the human race would not have been possible but for many great explorer-scientists who combined their love of adventure with their immense scientific curiosity.
Though Darwin had surmised that evolution of hominids was in Africa, very soon the majority opinion shifted to Asia as the most likely place for early hominid evolution.
Eugene Dubois gave up a prestigious academic career to go looking for the so called missing link between apes and humans, in the remote islands of the Malay archipelago.
He was rewarded by the find of what came to be known as the Java man in Indonesia. We now recognize this as the Homo erectus.
5. The focus shifted back to Africa in the 20th century.
Much of the fossil evidence for the current view on human evolution has come from the great rift valley in Africa spanning from Ethiopia to East Africa.
6. The husband and wife team of Louis Leakey and Mary Leakey were pioneers in the exploration for human origins in Africa.
7. Most of the studies of the Leakeys were done in the Olduvai gorge and the nearby Laetoli in Tanzania.
8. The Olduvai gorge is a steep-sided ravine from wherefossil remains of human ancestors have been found from as long as 2.5 million years ago. It is also a site from which very old stone tools dating to about the same time were unearthed.
These tools called Oldowan tools indicate that our hominid ancestors started using tools from as early as 2.5 million years ago.
9. Richard Leakey (son of Louis and Mary) and Donald Johanson (right). Richards digs near the Lake Turkana in Kenya and Johansons in the Afar region of Ethiopia helped discover landmark fossils.
10. A team of researchers excavating in northern Chad unearthed in 2002 the well-preserved skull and other fossilized remains of what they believe was an early human precursor, that lived six to seven million years ago. It is probablythe oldest known ancestor of humans. Named Sahelanthropustchadensis, it is believed to have walked upright, but not all scientists agree on this.
11. The term missing link is often misinterpreted by those who oppose the theory of evolution, particularly the creationists.
It is understandable to talk of a common ancestor, in this case a now extinct ape which led to the lineages of Chimpanzees and Bonobos on one hand and humans on the other. It is to be remembered that both groups have evolved in its own way for millions of years before taking the present characteristics.
Missing link between chimps and humans is that way absurd, because evolutionary theory does not postulate the existence of such a creature that is half human and half chimp.
12. It is generally agreed that upright posture and walking on two feet was the most important event that led to the evolution of the hominid branch.
This led to the freeing of the hand which in turn led to the making and use of better and better tools. With tool making and the precision and co-ordination required for it, the brain capacity became an important factor for natural selection to operate. The increase in brain size followed in successive hominids reaching a culmination in Homo sapiens.
13. How do we get clues regarding bipedalism from the available fossil evidence?
Foramen magnum is the large hole in the underside of the skull, through which the spinal cord passes. It is found towards the back in animals that walk on all four limbs like that of the chimpanzee on the left. In the bipedal and upright animals like humans, the foramen magnum is seen much more towards the center.
14. The way bones are joined together in the pelvis and foot and the shape of the leg bones and vertebrae also give us a good idea about bipedalism.
15. The skeleton of Lucy, the famous fossil of the definitely bipedal hominid discovered by Donald Johanson in the Afar region of Ethiopia dated to be about 3.2 million years ago. On the right is a reconstruction of how Lucy would have looked like.
Since then more remains have been unearthed of this creature named Australopithecus afarensis.
A afarensis had a small brain size like that of the apes. This is proof that bipedalism preceded increase of brain size during evolution of the hominids.
16. 3.6 million year old footprints (dated by radiometric methods) discovered by Mary Leakey in Laetoli.
The prints are strikingly different from those of a chimpanzee, and in fact are hardly distinguishable from those of modern humans. The only known hominid fossils of that age in that location are those of Lucy and her kind, the small-brained but upright-walking hominids classified as Australopithecus afarensis.
While the detailed interpretation of the prints remains a matter of debate, they remain an extraordinary and fascinating fossil find, preserving a moment in prehistoric time.
17. Homo habilis existed from 2.3 million to 1.6 million years ago. It displayed human like traits not seen in earlier hominids like the shape of its upper jaw. But they retained a number of ape like characters like long arms and short legs.
Homo habilis is believed to be one among the first tool users.
18. Homo habilis tools were simple stone flakes with a sharp edge. They probably used these tools for cleaving meat off of dead animals rather than hunting.
19. Homo ergaster which lived 1.9 million to 1.3 million years ago had a larger brain than Homo habilis.
Some regard this as a subspecies of Homo erectus.
20. Homo erectus which lived from 1.8 million to less than 100000 years ago was the first human ancestor to leave Africa and reach various parts of Asia and Europe.They had brain sizes varying fro 850cc in the older to about 1100 cc in the later specimens.
Many consider Homo erectus to be the direct predecessor of modern humans and the Neanderthals.
21. Homo ergaster and Homo erectus made tools which were more sophisticated than the stone flakes used by Homo habilis. The tools indicate that they were definitely hunters. These type of tools called the Acheulean tools have been recovered from all over the world and had remained unchanged for nearly a million years.
22. Homo erectus was the first to have definitely used controlled fire, though whether they made fire is debatable.
23. Neanderthal and modern humans. Both spread from Africa to Europe and Asia and co-existed till about 30000 years ago when the Neanderthals disappeared. There is difference of opinion whether to regard them as two sub-species of Homo sapiens or as separate species ie. H sapiens and H neanderthalis. Both the groups had similar brain size of about 1400 cc.
24. Brain size increased progressively during hominid evolution to the 1400 cc or so in the moderns and neanderthals.
We have seen that bipedalism preceded increase in brain size and that resulted in freeing of hands and its it use in fine co-ordinated movements.
This is reflected in the anatomy of the human brain.
25. This is the human brain. Areas shown in red and blue are those concerned with voluntarymovements and their coordination.
26. See the various parts of the body represented in the motor areas of the brain according to scale. Note that about one third of the area is just for the hand.
27. The Neanderthals were our closest cousins. They spread from Africa to the colder climates of Europe and Northern Asia earlier than us. Their body was more adapted to cold. They were stockier and had large noses and a heavy ridges on the brows.
28. Their tools were far more sophisticated than that of Homo erectus.
29. Reconstruction of how a Neanderthal girl would have looked like. We wouldnt have recognized her in a crowd of modern humans as someone belonging to a different species.
Did we interbreed with the Neanderthals? Current evidence from DNA isolated fromNeanderthal remains says no.
30. Both Neanderthals and modern humans buried their dead. Modern humans frequently buried other artifacts along with their dead indicating rituals.
Here is a Homo sapiens woman and a baby buried togetherin a cave in Israel some 100,000 years ago.
31. Homo sapiens tools were superior and used material like quartz. They also made new kind of tools like arrowheads.
32. One thing that seems to have set apart Homo sapiens from others is the capacity for abstract thought and expression.
Animal figures engraved in the Cussac cave (France) about 22000 years ago.
33. A 24000 year old sculpture of a womans head (France)
34. The family tree of hominids spanning about 4 million years. It has branching shape some branches leading to dead ends.
35. There have been two theories regarding the origin of modern humans ie. Homo sapiens sapiens.
One view called the Multiregional model is that modern humans arose separately in the different continents from the predecessor species ie. Homo erectus.
The second view dubbed the Out of Africa