Hominines Lecture 18
Many of the crucial differences between plants and animals arise from this simple but fundamental difference: They can photosynthesize; we can’t.
T
he last two lectures described evolution in general, focusing on those evolutionary lines that would eventually lead to our species. Now we are ready to ask how our ancestors evolved from the primates. First we must be clear about our place in the biological world. We have seen that modern systems of biological classi¿cation (or “taxonomy”) build on the work of Carl Linnaeus (1707–1778). The multiple levels of a taxonomy (from superkingdom to species) allow us to de¿ne each species uniquely so as to reveal its position in the huge family tree of life. You and I belong to the “superkingdom” of eukaryotes (we’re made from eukaryotic cells); the “kingdom” of animals (we’re not single-celled, nor are we plants or fungi); the “phylum” of vertebrates, or “chordata” (we have backbones); the “class” of mammals (we’re furry, warm-blooded, and our young develop within the womb); the “order” of primates (lemurs and monkeys); the “family” of hominoids (great apes); the “subfamily” of hominines (bipedal apes); the “genus” Homo; and the “species” Homo sapiens. (Note that classi¿cation systems differ in details.) In short, we are eukaryotic, multi-celled mammals from the order of primates. The order of primates appeared about 65 million years ago, at about the time of the Cretaceous asteroid impact. The primates include all monkeys and lemurs, from tarsiers to gorillas, as well as humans! Primates share some distinctive features. Because early primates lived in trees, they developed stereoscopic vision and grasping limbs. Perhaps because visual information requires a lot of processing capacity (for brains as for computers), primates have disproportionately large brains for their size. (Elephants have huge brains, but their bodies also use a lot of computing capacity so it’s brain size relative to body size that really counts.) Larger brains generally imply longer lives to take advantage of the brain’s capacity to learn. The sense of smell is less important, so most primates have small snouts and Àattish faces. 81
