Human beings are a species of animal, belonging to the vertebrate group called mammals. All mammals have hair and females are able to produce milk to feed their babies. Some female mammals lay eggs (Monotremes e.g. platypus, echidna) and others have mostly external pregnancies (Marsupials e.g. opossum, koala, kangaroo). The females of all other mammals have internal pregnancies where the baby is nourished through an organ called a placenta.
There are four clear genetic groups of placental mammals, all with helpfully unpronounceable names:
- Afrotheres – 146 species; evolved in Africa and mostly stayed there; including elephants, manatees, aardvarks, tenrecs & elephant shrews;
- Xenarthrans – 31 species; evolved in South America and mostly stayed put; includes sloths, anteaters & armadillos;
- Laurasiatheres – 2,154 species; probably evolved in the Northern Hemisphere but now widespread; includes hedgehogs, bats, horses, rhinos, deer, pigs, whales and ALL true placental carnivores (cats, dogs, weasels, bears, seals etc.);
- Eurachontoglires – 2,480 species (of which 1,999 are rodents) uncertain origins, found on every continent today – includes rodents, rabbits & primates.