Rất đơn giản hóa gia đình cây (cladogram) của quá trình tiến hóa vượn nhân hình: Khoảng 6 triệu năm trước có một sự chia rẽ trong gia đình vượn với một chi nhánh dẫn đến các loài vượn lớn khác và một chi nhánh dẫn đến sự tiến hóa của loài vượn đầu tiên được dominantly đi bằng hai chân | 174 Evolutionary echoes and the human camel Fig. Very simplified family tree cladogram of hominid evolution About 6 million years ago there was a split in the ape family with one branch leading to the other great apes and one branch leading to the evolution of the first ape-like species to be dominantly bipedal an Australopithicus species which in turn led to the evolution of the Homo family about 2 million years ago. Homo sapiens only evolved as a distinct species about 200000 years ago. While Homo erectus had spread through Euro-Asia as well as Africa over a million years ago Homo sapiens did not leave Africa until about 65 000 years ago. In evolutionary terms humans are relatively unusual in another way whereas most species continue to reproduce throughout life in the absence of disease the phenomenon of reproductive failure well before death is essentially unique to the human Therefore natural selection has not acted significantly to reduce the probability of disease in humans where that disease appears in later life. Putting these phenomena together it is not surprising that modern humans often now live in environments that can induce disease in middle age. In itself this is not a novel conclusion. However what is novel is the increasing realisation that evolutionary echoes of other processes acting in early life interact with the current environment to increase the risk of such disease. These echoes are retained in the set of PARs which have been essential processes over evolution to ensure the normal survival of mammalian species through transient environmental change. As humans have experienced recent and massive environmental change in the absence 3 Chimpanzees retain fertility until old age whereas rhesus monkeys have symptoms of reproductive failure in later life human females lose reproductive competence in middle age. 175 The post-evolutionary human and PARs of evolutionary progression these responses now lead to a particular set of .
