Download Concepts in the study of Evolution

Concepts in the study of Evolution
Your reading has discussed some concepts related to the study of biological evolution that we
have not discussed in class. I will attempt to summarize a few of these concepts here.
Homologous and Analogous Structures - Evidence for common ancestry can be found in
homologous structures. Consider the wing of a bat and your hand/forearm. The skeletal structure of
both contains the radius and ulna, carpels and metacarpals, and phalanges. So the underlying structure
is very similar yet the functions of the two are quite different. On the other hand (NPI), the wing of a
bat and wing of a insect are analogous structures because while the underlying structures are
fundamentally different, the function in both cases is flight.
Coevolution - When species evolve in response to one another, they co-evolve. This is evident in the
coevolution of specific pollinators for specific plants. The plant and the pollinator evolved in response
to one another. This example results in a symbiotic relationship between the two. Likewise, parasites
evolve in response to the evolution of their host. Parasitism is a form of symbiosis. Some predators
and prey have coevolved. While it may be difficult to imagine how a population of prey could benefit
from their primary predator, consider that the predator may have the effect of strengthening the prey in
an evolutionary sense. The prey would likewise evolve to enhance the evolution of its predator.
Convergent Evolution - During the Paleozoic Era, amphibians diverged from fish. Later, reptiles
diverged from amphibians and during the Mesozoic Era, mammals diverged from reptiles. Then
during the Cenozoic era, some mammals returned to a life in the ocean - dolphins. In the process of
adapting to the life aquatic, dolphins came to resemble a very distant relative, the shark. The
similarities of these two is a result of convergent evolution. Converge = to come together. Diverge =
to move apart.
Gradualism - The concept that evolution is slow and steady change as envisioned by Darwin.
Punctuated Equilibrium - The concept that evolutionary change is not steady, but rather, there are
periods of relative equilibrium punctuated by periods of rapid divergence of species. Mass extinctions
create biological vacuums in environments and ecosystems and plays a major role in this punctuated
equilibrium. Punctuated equilibrium is now considered to be a much more accurate description of the
pace of evolutionary change than is gradualism.
Lamark, and the theory of use and disuse - Before Darwin, Jean Baptist Lamark (a French scientist)
proposed a theory for how species evolve. He said that if organisms used some feature with greater
regularity, then they would somehow pass this trait to their offspring. The most commonly used
example of Lamarkism is the long neck of the giraffe. While Lamark's theory has long since been
discredited, it remains a staple of evolutionary study because 1. At least he came up with a theory, and
2. It shows yet again that scientific views can change. FYI: Very recent studies in the area of
epigenomics provide evidence that Lamark was not entirely wrong. Stay tuned.