There was a great diversity of ape species in the Miocene, with dozens of species known from the fossil record across Africa, Europe, and Asia. Hominins are species on our branch of the hominoid tree after the split with the chimpanzee & bonobo line, including all of the extinct species and evolutionary side branches (Figure 1). The Human-Chimpanzee Last Common Ancestor (HC-LCA) is the species from which the hominin lineage and the chimpanzee & bonobo lineage diverged. In order to understand the evolution of any species, we must first establish its ancestral state: what sort of animal did it evolve from? For our lineage, this requires that we try and reconstruct the Last Common Ancestor of humans and chimpanzees (marked "A" in Figure 1). We begin this discussion of our species' evolution in Africa, near the end of the geological time period known as the Miocene, just before our lineage diverged from that of chimpanzees and bonobos. The fossil record, along with studies of human and ape DNA, indicate that humans shared a common ancestor with chimpanzees and bonobos sometime around 6 million years ago (mya). Among the great apes, our closest relatives are the chimpanzees and bonobos (Figure 1). Our immediate evolutionary family is comprised of the hominoids, the group of primates that includes the "lesser apes" (siamangs and gibbons) as well as the "great apes" (chimpanzees, bonobos, gorillas, and orangutans). The implications are breathtaking if we could travel back far enough in time, we would find common ancestors between ourselves and every other living organism, from porcupines to flamingoes to cactuses. Darwin's great insight, and the unifying principle of biology today, is that all species are related to one another like sisters, cousins, and distant kin in a vast family tree of life.
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