Born in Africa_ The Quest for the Origins of Human Life - Martin Meredith [2]
Even Darwin’s scientific colleagues found difficulty in accepting some of his ideas, especially his emphasis on natural selection as being the mechanism of change. One eminent scientist dismissed natural selection as the ‘law of higgledy-piggledy’. Most scientists disliked the idea that evolution could be an open-ended process of adaptation and divergence. They preferred to believe that evolution was guided inexorably in the direction of progress towards humankind.
Nor did they concur with Darwin’s model of an evolutionary tree with numerous branches to explain the extent of biological diversity. The model they favoured was based on linear development—a tree of life with a main trunk leading upwards from ‘lower’ organisms at the bottom to humans at the top—a modernised version of the ancient notion of a Chain of Being that had previously been used to explain life on earth. They remained convinced that evolution was all part of a purposeful process, directed towards a predetermined goal.
There was also disagreement about the way that human faculties were said to have developed. Darwin speculated that human ancestors had moved from a forest environment onto the open plains of Africa, acquiring the ability to walk upright on two legs as a better means of locomotion. Bipedal locomotion had thus been the key breakthrough—the first attribute separating human ancestors from the ape masses. It had freed their hands for primitive toolmaking, which in turn had stimulated the growth of their intelligence. Other apes meanwhile had stayed in the trees, continuing to use their hands as a means of locomotion; they had consequently never acquired the need for additional intelligence. In other words, Darwin regarded the development of higher human faculties as no more than a by-product of a change in the mode of locomotion by one particular group of African apes.
The theory supported by most other scientists was that the brain had been the original driving force behind human evolution. Impressed by the large size of the modern human brain, they believed that it must have been sheer brainpower that had propelled humans along the road to preeminent status.
Darwin’s suggestion that Africa was the cradle of humankind was also challenged. An influential German biologist, Ernst Haeckel, argued that Asian apes—orang-utans and gibbons—were more closely related to humans than African apes were, making Asia a more likely birthplace. Haeckel’s tree of life also differed from Darwin’s. He proposed the existence of an intermediate link between humans and apes that he called ‘Ape-like Man’, or Pithecanthropus. His reasoning was that the human capacity for speech must have required more than a single evolutionary step in which to develop. Haeckel described this hypothetical link as a hairy, primitive creature with a long skull and protruding teeth that walked semi-erect. This idea of an intermediate figure from the past became popularly known as ‘the missing link’.
Whatever theories scientists chose to air, there was scant evidence on the ground to support any of them. Only one possible candidate for the missing link had come to light: parts of a skeleton unearthed in 1856 by quarry workers clearing out a limestone cave in the Neander Valley near Düsseldorf in Germany. The remains—the top of a cranium, some leg and arm bones—belonged to an individual who was evidently human but unlike any other human known. The individual was heavily built, short in stature, with prominent ridges above the eyes and a low, receding forehead—similar to an ape but with a modern-sized brain.
The reaction of scientists to this discovery was mixed. The biologist