occurred after brain size reached modern propor-
tions? These fossils from Sima de los Huesos (“Pit
of the Bones”), Sierra de Atapuerca, Spain, are an
important part of the puzzle. They are the best col-
lection of Homo fossils from a single site. Although
the remains possess cranial capacities overlapping
with the average size of contemporary humans, the
scientists who discovered them place them in the
species Homo antecessor. Dated to 400,000 years
ago, these fossils fit into the complex period of our
evolutionary history when brain size and cultural
capability began to separate.Challenge Issue With the appearance of
the genus Homo 2.5 million years ago, our
ancestors—with their increased brain size and
emerging cultural repertoire—were better able
to meet the challenges of survival. We know that
without this brain expansion, reliance on culture
could not have occurred, but we are not certain of
the exact relationship between biological change
and cultural capacity. Does each cultural innova-
tion mark the appearance of a new species? Does
a 20 percent increase in brain tissue do the same?
And what about all the cultural changes that have
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