Figure 7.20: The bones in your arms and hands have the same bone pattern as those in
the wings, legs, and feet of the animals pictured above. How have the bones adapted for
different uses in each animal? ( 6 )
vertebrae that come under your hips. These are called your tailbone. We do not use these
small vertebrae; they are further evidence of our evolution.
Embryological Evidence
Some of the oldest evidence of evolution comes from embryology, the study of how organisms
develop. An embryo is an animal or plant in its earliest stages of development, before it is
born or hatched.
Centuries ago, people recognized that the embryos of many different species have similar
appearances (Figure7.21). The embryos of some species are even difficult to tell apart.
Many of these animals do not differ much in appearance until they develop further. Many
traits of one type of animal appear in the embryo of another type of animal. For example,
fish embryos and human embryos both have gill slits. In fish they develop into gills, but in
humans they disappear before birth (Figure7.22).
The similarities between embryos suggests that these animals are related and have com-
mon ancestors. For example, humans did not evolve from chimpanzees. But the similarities
between the embryos of both species may be due to our development from a common an-
cestor with chimpanzees. As our common ancestor evolved, both humans and chimpanzees
developed different traits.