The hominid family tree has 7 widely acknowledged genera: Sahelanthropus, Orrorin, Ardipithecus, Kenyanthropus, Paranthropus, Australopithecus, and Homo. There were doubtlessly more.
Hominins were born when grasses were on the rise. ~ American paleoanthropologist Ann Gibbons
Climate was a likely driver of the radiation of early hominids, at a time of warming, when forests thinned. Social factors may have also been instrumental, but there is no evidence of this, nor would there be even if it were so.
The fossils of the earliest hominids were found in Europe. Living 9.6–7.2 MYA, Ouranopithecus appears a mixture of ape and hominid.
The fossils of the other early hominids were dug in central east Africa. Later finds range more widely, to the west and south.
Teeth are the most common fossils, because they withstand the punishments of time better than any other body part. Dental remains, by the shape of various teeth and their wear patterns, yield indications of diet.
To estimate evolution, early hominids have been compared to our closest relatives: chimpanzees and gorillas. This apples-and-oranges comparison is complicated by lacking any significant fossil record of apes.
Once asked if hominid fossils spoke to him, Kenyan fossil hunter Kamoya Kimera replied: “yes, but you can’t understand them!”