Returning to Africa 10-15 million years ago, one possible scenario explaining this first phase of human evolution is that the ancient apes in the west continued to live in dense, humid, tropical forests, spending much of their time in the trees, eating fruit, with perhaps no significant pressure leading them to evolve significantly. However, ancient apes in the east had to adapt to a new life in a drier more open environment. Trees became fewer and farther apart, and eastern apes would have to spend more time on the ground, with less shade, avoiding predators and ranging further to find food. Possibly because of such pressures, about seven million years ago in East Africa there was a divergence of an ancient species of ape into the ancestors of gorillas and the ancestors of chimpanzees and humans, and about 5.5 million years ago there was a further divergence when the ancestors of humans separated from their nearest relative – the chimpanzee. The hominid branch had begun.

Hominid Branch

It is fascinating to realise that the difference between our DNA and present day chimpanzees is only 1.2%, and apparently we share O-type blood with them and no other animals.

1.3 Hominids

Relatively shortly thereafter (about 4.5 million years ago) there is evidence that our ancestors became bipedal, a hugely significant evolutionary step. At present the actual cause of this advance is uncertain, but there are several likely benefits. Bipedalism proves to be much more energy efficient, by a factor of 4 over apes on all fours, giving better running endurance; the need to move quickly with simultaneous good visibility might well have given the edge on survivability to some of those apes that spent more time upright; standing upright might keep the body cooler using less water; and it also leaves the hands free to carry food any distance.

A study of climate change around this time showed that there were two significant periods of dramatic cooling between 7 and 4.5 million years ago, and 3 and 2 million years ago. At the start of the latter period there was much snow and ice in Antarctica, but little in the Arctic and Greenland, so sea levels were much higher. Around 2.5 million years ago oceanic and atmospheric circulation patterns changed, starting a permanent build-up of ice and snow in the North Polar Region, so that by about 2 million years ago sea levels had dropped significantly. During these huge worldwide climate changes, significant evolutionary changes to animals on land and sea took place. However, much is speculation in this early period as the amount of evidence available to trace the origins of mankind from its ancient ape ancestor to the present Homo Sapiens is woefully inadequate. Fossil finds are very few and far between with considerable time gaps and usually very incomplete specimens. This paucity of data explains the lack of clarity of our ancestry and the controversy that surrounds it, as new discoveries throw earlier ideas back into the melting pot. However, as the first 2-3 million years of hominid fossil records are entirely restricted to Africa it is almost certain that humans originated there.