5 Steps to a 5 AP Biology, 2014-2015 Edition

146 ❯ STEP 4. Review the Knowledge You Need to Score High

deduce phylogenetic relationships. By the end of the nineteenth century, it was clear this

law rarely holds. The real development of organisms differs in several important ways

from Haeckel’s schemes.

3. Vestigial characters.Most organisms carry characters that are no longer useful, although
   they once were. This should remind you of our short discussion about why organisms
   are not perfectly adapted to their environments (because the environment is constantly
   changing). Sometimes an environment changes so much that a trait is no longer
   needed, but is not deleterious enough to actually be selected against and eliminated.
   Darwin used vestigial characters as evidence in his original formulation of the process
   of evolution, listing the human appendix as an example.
   Keep in mind that the kinds of evidence we’ve described are often found in the fossil
   record–the physical manifestation of species that have gone extinct (including things like
   bones as well as imprints). The most important thing to remember is that adaptations are
   the result of natural selection.

Macroevolution

Biologists distinguish between microevolution and macroevolution. Microevolution

includes all of what we have been discussing so far in this chapter—evolution at the level

of species and populations. Think of macroevolutionas the big picture, which includes the

study of evolution of groups of species over very long periods of time.

There are disagreements in the field as to the typical pattern of macroevolution.

Those who believe in gradualismassert that evolutionary change is a steady, slow

process, while those who think that evolution is best described by the punctuated equi-

libria modelbelieve that change occurs in rapid bursts separated by large periods of

Gradualism Punctuated equilibrium

Constant gradual change

Time Stasis

Speciation Sudden, rapid change

Speciation

Variation

Figure 12.3 Gradualism versus punctuated equilibrium.