Modern humans belong to the primate family known as hominids or “ great apes “.
Even chimpanzees and the gorillas are classified as hominids.
Modern humans share a common ancestor with chimpanzees from about 8 million years ago .
Since that time various species of bipedal hominids have evolved in Africa , some of which are direct ancestors of modern man, while others simply went extinct.
The remains of Sahelanthropus tchadensis were discovered in Chad, date back to about 7 million years ago and may be a common ancestor of both humans and chimpanzees.
One million years later, Orrorin tugenensis lived in Kenya and walked upright, but still adapted to climbing trees.
Ardipithecus ramidus lived in Ethiopia about 4.4 million years ago , he walked erect and had smaller teeth, more human than other monkey species, but his brain size was smaller than modern chimpanzees and only 20% the size of modern humans .
In any case, the Australopithecus afarensis remains the only well-defined hominid in all of Africa, between 4 and 3 million years ago.
The characteristics of afarensis are a mosaic of evolutionary traits and archaic elements:especially the skull is surprising , very small ( 380-530 cc ) and with a simian appearance. The molars and the premolars they are very large compared to their body size ( 1.05 meters high by 27 kg. of weight ) but they are not particularly specialized. The palate and the mandible they have decidedly primitive traits. The face is prognate. Males and females differed in size, with such a marked difference in shape as to resemble our gorilla cousins , where males can weigh twice as much as females.
Lucy was human from the head down, remaining ape where spectacular development could be expected:skull and brain.
This evolution is of particular interest because it suggests that homination did not occur gradually, affecting all anatomical structures at the same time.
Some characteristics, such as the standing position , developed first, conditioning subsequent adaptations, according to the natural selection imposed by an environment, such as the African one of 3 million years ago , which was changing more and more rapidly.