Final answer:
A hominid encompasses all modern and extinct great apes including humans, while a hominin refers specifically to species closely related to humans, characterized by bipedalism and including genera like Homo and Australopithecus.
Step-by-step explanation:
A hominid refers to any member of the family Hominidae, which includes modern and extinct great apes: humans, gorillas, chimpanzees, and orangutans, as well as their ancestors. However, the term hominin is more specifically used to describe the group that includes modern humans, all our ancestors, and other species that are more closely related to us than to chimpanzees. This includes the genera Homo, Australopithecus, Paranthropus, and Ardipithecus. Hominins are characterized by bipedal locomotion—walking on two legs—and various other evolutionary markers such as increased brain size and opposable thumbs.
Human Evolution and Hominins
The process of human evolution can be traced back to the divergence from a common ancestor with chimpanzees, approximately six million years ago. Bipedal hominins have included several groups within our lineage, such as Australopithecus, Homo habilis, and Homo erectus, as well as species considered to be our 'cousins,' like the Neanderthals and Denisovans.