Lecture 21:
Homo sapiens
—The First Humans
Currently, there are two competing explanations for the origins of Homo
sapiens. The “multi-regional hypothesis,” defended by Milford Wolpoff and
Alan Thorne, argues that our species evolved gradually throughout Africa
and Eurasia from Homo ergaster. It implies that most hominines in this era
belonged to a single, evolving species, with regional variants that show up
today in racial differences. However, most anthropologists are skeptical
that individuals could remain suf¿ ciently interconnected over such large
distances to remain a single species.At present, most paleontologists prefer the “Out of Africa” hypothesis,
according to which our species evolved quite rapidly in Africa within the last
250,000 years. This theory builds on recent developments in evolutionary
thought and dating techniques. In their theory
of “punctuated equilibrium,” Stephen Jay
Gould and Niles Eldredge showed that the
pace of evolution can vary signi¿ cantly, so
that sometimes new species can evolve within
thousands rather than millions of years.One mechanism for rapid evolutionary change
is “allopatric speciation.” If individuals at the
edge of a species’ range get cut off for many
generations, they may diverge rapidly from
a parent population because variations can
spread rapidly in small populations. Besides, such groups may already be
statistically atypical. Allopatric speciation may explain the rapid species
formation Darwin observed on the Galapagos Islands and the sudden
appearance of modern humans.Modern genetic dating techniques show that modern humans are closely
related and probably evolved within the last 250,000 years. The fact that the
greatest variation appears within Africa suggests that that is where humans
have lived longest. Finally, the earliest fossil evidence of anatomically
modern humans comes from Africa, and the oldest remains of modern
humans are about 160,000 years old.I will argue in the
rest of this course
that human history
really begins
between 200,000 and
300,000 years ago,
somewhere in Africa.