A second vital type of evidence for understanding hominine evolution comes
from studies of closely related species that are still alive today. Richard
Leakey’s former students, Jane Goodall and Dian Fossey, pioneered the
study of apes in the wild. They showed that the great apes have complex and
clearly de¿ ned social relationships that differ from species to species: For
example, males compete for dominance. They also showed that humans are
not the only great apes to use tools. For example, chimps often strip leaves
from sticks to ¿ sh out termites from termite mounds. Though no apes make
tools as sophisticated as those of habilis, this ¿ nding undermined Leakey’s
claim that habilis was the ¿ rst great ape species to use tools.
The most recent technique for studying human evolution uses genetic
evidence from living species. The evolution of genetic dating techniques
counts as one part of the “chronometric revolution” described in Lecture
Four. Genetic dating was pioneered by Alan Wilson and Vincent Sarich in
the 1960s. How does it work? Many genes are not expressed in the physical
body, so they do not all affect a species’ “¿ tness.” Such genes can therefore
change randomly, so we can use statistical methods to estimate how much
random genetic change there has been between two different species. By
calibrating these differences against other evidence (such as the knowledge
that mammal species diverged rapidly after the Cretaceous extinctions of
65 million years ago), we can estimate when two species may have shared
a common ancestor. When they ¿ rst proposed the idea, Wilson and Sarich
met with great skepticism, but since then, genetic dating has become a
fundamental tool for the study of evolution in general. Genetic dating
techniques have revolutionized our understanding of human paleontology by
showing that the DNA of humans and chimps differ by little more than 1%.
This suggests that the two species had a common ancestor about 7 million
years ago, rather than 15–20 million years ago as suggested by earlier
studies of skeletal remains. This date establishes a clear time frame for
the history of human evolution. Such techniques are particularly important
because so few fossil remains survive from this era. We’ve seen some of
the evidence used to construct the story of human evolution, and now we
can complete the story. The next lecture asks: What was it that made our
species so different? Ŷ