Tetsuro Matsuzawa writes:

The most recent common ancestor of chimpanzees and humans lived between five and seven million years ago. This shared heritage became evident when sequencing revealed a 1.2% DNA difference between species. Chimpanzees have a living sister species, bonobos, that is equally closely related to humans. Both chimpanzees and bonobos are found only in Africa; this is also true of gorillas. Chimpanzees and humans shared a common ancestor with gorillas between eight and nine million years ago. Another species of great ape closely related to humans are orangutans, which live in Southeast Asia, mostly on the islands of Borneo and Sumatra.

The family Hominidae consists of four genera: humans, chimpanzees (and bonobos), gorillas, and orangutans. The most recent common ancestors of hominids is thought to have lived around fourteen million years ago. In 2019, the International Union for Conservation of Nature listed no less than 512 living species of primates belonging to seventy-nine genera. These species were previously classified as hominids, gibbons, old-world (Afro-Eurasian) monkeys, new-world (American) monkeys, lemurs, and prosimians. With the exception of humans, all the living species of primates reside in Africa, Asia, and Central and South America.

Japan has its own indigenous monkey species in the Japanese macaque, which are sometimes referred to as snow monkeys. The monkeys found in the Shiga Kogen area of central Japan have become famous as the only species known to bathe in hot springs during winter. Another monkey community living on the tiny island of Kōjima near the southern tip of Japan is known for washing sweet potatoes. To wash away the sand from the potatoes they pick up from the beach, the monkeys carry the potatoes to the shallows and dip them in the sea, where they acquire a salty taste. This behavior was first observed in 1953 and is passed from one generation of monkeys to the next. The sweet-potato washing observed on Kōjima was the first example of cultural behavior found in nonhuman animals. [Continue reading…]