1.2 Africa

Some 15 million years ago Africa was covered in tropical forests from east to west, producing large quantities of fruit that sustained a number of different species of ape and monkey. At the time there were more ape species than monkey, but today this is reversed and there are only three great African apes remaining, gorilla and two species of chimpanzee. Over the next few million years there were huge geological upheavals in the East of Africa, thought to be caused by a fault in the Earth’s crust, on a line from the Red Sea, through the present Ethiopia, Kenya, Tanzania and into Mozambique. As a result some parts of the land rose to form a mountain range up to 3000 metres high, and others sank to form lakes, creating the 3000-mile long Great Rift Valley, one of Earth’s major features visible from space.

So, this region had a very diverse landscape of lakes, rivers, high plateaus and more arid plains. This changed the climate significantly between east and west as the mountains affected the rainfall pattern and it also formed a significant barrier to animal movement.

Rift Valley - source Wikipedia US Geological Society

It is apparent that when a species of animal suffers long-term stress it is likely to evolve in ways to reduce the stress. So if the climate changes and, for example, the normal source of food declines over an extended period, the species under such stress, in this case hunger, will have to adapt to survive. This mechanism operates in that those members who are marginally better at accommodating the changes will breed more successfully than those who do not and the species slowly migrates to the “fittest”, which in this case is the “fittest for purpose” rather than necessarily physically stronger. If the stress is too sudden or the adaptation inadequate then the species dies out – as many have done in the past. Two examples of such relatively sudden stress are firstly, the warming of the oceans some 250 million years ago that caused inadequate temperature differential to allow polar water to sink so the ocean currents stopped. There was insufficient oxygen in the water to support marine life and the stagnant oceans released poisonous hydrogen sulphide gas that killed land animals, resulting in 90% of living things dying. The second was the extinction of 70% of living things, including all the non-flying dinosaurs, as a result of the collision of a huge asteroid, the size of Everest, with the earth (Mexico) some 65 million years ago, throwing so many billions of tons of dust into the atmosphere it caused darkness for years.