What evidence has allowed scientists to conclude that the common ancestor of modern chimps
and humans lived around 7 million years ago?
a. Stone tool usage began showing up in the human lineage around 7 million years ago, and
chimps do not use stone tools.
b. From the changes scientists have observed in chimps over the past 200 years, they predict it
will take at least 7 million years for today’s chimps to evolve into more humans.
c. Biological molecules such as proteins and DNA reveal differences between humans and
chimps that would have taken around 7 million years to accumulate.
d. Scientists know from whale evolution that it takes around 3.5 million years for brain size to
double in volume in a species’ lineage, and chimp brains are 300 cubic centimeters, while
human brains are around 1,300 cubic centimeters.