As you read the following quote from Stephen Jay Gould, think about
how he compares upright posture to the enlarged brain.
Upright posture is the surprise, the difficult event, the rapid and
fundamental reconstruction of our anatomy. The subsequent enlargement of our brain is, in
anatomical terms, a secondary epiphenomenon, an easy transformation embedded in a general
pattern of human evolution. As a pure problem in architectural reconstruction, upright
posture is far-reaching and fundamental, an enlarged brain superficial and secondary. But
the effect of our large brain has far outstripped the relative ease of its construction.
(From "Our Greatest Evolutionary Step," in The Panda's
Thumb. [London: Penguin, 1980])
A second major adaptive advantage that appeared later in human evolution
was bigger brains. Fossil evidence allows us to trace the development of the brain as it
increased threefold over the past 3 million years. Early hominids such as the australopithecines
had brains the size of modern apes (400 to 500cc). Homo habilis, with a brain of
about 650cc, was probably the first hominid discovered to make and use stone tools. As
brain size increased, new capabilities evolved as well, giving these early humans
abilities to adapt to and modify their environments. Tools became more sophisticated and
eventually humans developed culturally as well as biologically.
Another earlier hominid, Homo erectus (with an approximate brain
size of 900cc), was the first to develop humanlike culture. Homo erectus used
tools, including hand axes, made fires, and were the first hominid species believed to
have spread from Africa into Asia. Modern humans, Homo sapiens (with brains ranging
from 1200 to 1600cc), have even more sophisticated capabilities, probably due to
neurological developments within the brain rather than size alone. Brain size gives only
limited information about the internal structure and capabilities of the brain. One later
hominid species, Homo neanderthalensis, had a brain size of over 1300cc, but is
considered to have been much less sophisticated than, and possibly even driven to
extinction by, modern humans.