Encyclopedia of Evolution.pdf - Online Reading Center

Flores Island people
Christopher Stringer, head of Human Origins at the Natural History Museum in London, displays a skull of a Homo erectus, left, a cast taken from the
skull of the newly discovered Homo floresiensis, center, and the cast of a modern Homo sapiens skull during a news conference in London, October ,
00 . (Courtesy of Richard Lewis/AP)
this was the only known example of human evolution going
in the direction of smaller bodies and brains. The evolutionary
myth (myth in the sense of a big story that helps humans
understand their place in the world) as understood by most
laymen is that evolution produced ever larger and brainier
humans. Human evolution had frequently been portrayed
as a march upward (see progress, concept of). For people
who adhered to the evolution myth rather than evolutionary
science, H. floresiensis came as a shock.
Why might these hominins have evolved small size? On
islands, immigrant animal species with large bodies evolve
smaller bodies, and immigrant animal species with small bodies
evolve larger bodies. Extremes of body size may be the
result of competition: Animals can avoid direct competition
with other animals of their species either by being bigger,
and overpowering them, or by being smaller, and avoiding
competition by specializing on more limited resources. This
is why islands may have big rodents and small elephants.
Flores Island itself had giant tortoises, giant lizards, ele-
phants as small as ponies, and rats as big as hunting dogs, at
the same time that H. floresiensis lived there. Isolated from
competition with other H. erectus, the Flores islanders may
have been free to evolve into smaller form. Smaller bodies
can survive more easily upon limited food supplies than can
larger bodies.
One particularly surprising aspect was the very small size
of the brain. The cranial capacity of H. floresiensis was in the
range of chimpanzees and australopithecines. Amazingly,
despite such small brains, the Flores Island people continued
making stone tools and building fires, neither of which
activities had been invented by australopithecines. Presumably
it takes less brain power to maintain a technological tradition
than to develop one. Although it has been suggested
that the smaller brain might have resulted simply from the
overall decrease in body size (see allometry), in this case
the decrease in brain size was disproportionately more than
the decrease in body size: H. floresiensis bodies were about
half the size, but their brains only a third the size, of those