Hominines.........................................................................................

LECTURE

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 À attish faces.