Life Sciences: Theories of Evolution

Life Sciences: Theories of Evolution

We'll look at the interplay between population genetics and environment. Are traits individually acquired or do entire populations evolve? The flying hamsters and a few other notable experiments will provide the answers.

Theory of Acquired Characteristics

While having lunch with some other students in our building, we learn about their theories regarding the evolution of traits. They tell us they believe that the evolution of new anatomical factors is driven by necessity. Similarly, if an organism doesn't need a structure, that structure will become smaller and less developed because of disuse. The idea that characteristics an organism acquires during its lifetime can be passed on to its offspring is attributed to the scientist Jean-Baptiste Lamarck. This theory is called heritability of acquired characteristics or Lamarckian inheritance.

Lamarckian Inheritance

Under this theory, a giraffe that stretches its neck to reach leaves in higher branches of trees would pass on stronger necks to its offspring, which would enable longer reach and eventually result in the evolution of giraffes with longer necks.

Similarly, the theory proposes that the disuse of the small toe in mammals, such as pigs, caused it to disappear over time. We might say that the theory of acquired inheritance is akin to the adage Necessity is the mother of invention. The need for a trait drives the evolution of that trait.

Pinciples of Darwanian Evolution

For a given situation, new combinations of a gene could provide a competitive advantage for individuals of a population. Let's consider an example: suppose there are variations in size and strength of wings within an island hamster population. Hamsters with stronger, larger wings can fly farther than hamsters with smaller wings. However, since food and mates are plentiful on the island, the difference isn't really that important. Now, suppose the giant volcano on that island erupts, and the flying hamster habitat is completely destroyed.

Pinciples of Darwanian Evolution

The hamsters with larger wings are strong enough to make it to new islands, while the weaker ones are stuck on the ruined island or simply can't make it all the way to the other island. In the end, the significant alteration to the environment resulted in hamsters with larger, stronger wings. These are the basic principles of the theory of evolution that was proposed by Charles Darwin.

Theories of Evolution

Lamarckism vs. Darwinism

Multiple Choice

Which of the following is NOT a principle of Darwin's theory of evolution?

• An individual can evolve.

• Individuals with different genotypes may pass on their traits at different rates to the next generation.

• Some traits give an individual a better chance of surviving.

• Traits are heritable.

Multiple Choice

Which of the following is an example of natural selection? I. Albino animals are rare in nature because they are easy for predators to find. II. The fastest gazelle is least likely to be eaten by a lion. III. The gorilla that is strong enough to become alpha male is the most likely to pass on his genes.

• I and II

• I and III

• II and III

• I, II and III

Multiple Choice

Which of the following statements does NOT represent the idea of heritability by acquired characteristics? I. A body builder develops stronger muscles during the course of his life, so his son will be strong as well. II. A cat that lost its tail will produce offspring with shorter tails. III. Over time, a population of heavily striped zebras increased over those without as much striping, as the heavily striped ones had a competitive advantage over the zebras with fewer stripes, and were, therefore, better able to reproduce.

• I and III

• I

• III

• II

Multiple Choice

_____ can be defined as a change in a characteristic within a population over time.

• Evolution

• Lamarckian inheritance

• Natural selection

• Creationism

Multiple Choice

The study of the genetic variation within a population is known as:

• Population genetics

• Lamarckian inheritance

• Population dynamics

• Natural selection