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Theories of Evolution: Lamarck vs. Darwin

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  • 0:36 Population Genetics
  • 1:00 Lamarckism
  • 2:51 Darwinian Evolution
  • 5:00 Lamarckism or Darwinism?
  • 6:29 Summary
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Lesson Transcript
Instructor: Greg Chin
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.

Population Genetics Project

Given the burgeoning success of flying hamster research and our fascination with the little rodents, you and I have decided to do our senior research thesis in Adrian's lab. A lot of the other researchers in Adrian's lab are focused on studying the genetics and molecular biological function of specific genes and proteins in the flying hamsters. I think it would be interesting to study the genetics of an entire population of hamsters rather than studying just a single gene. The study of genetic variation within a population is called population genetics.

Since we seem to be working together so well, let's go ahead and collaborate on our population genetics projects. Let's think about the mechanism of evolution before we get started, which begs the question: what is evolution? For now, let's think about evolution as a change in a characteristic within a population over time. As we learn more about population genetics, we'll be able to further refine this definition.

Theory of Acquired Characteristics

The evolution of longer necks in giraffes is an example of Lamarckian inheritance
Acquired Characteristic
Jean-Baptiste Lamarckheritability of acquired characteristicsLamarckian 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.

Principles of Darwinian Evolution

Now, our classmates' theory seems pretty logical, but it's also a good idea to consider alternative possibilities. From our previous experiments, we know that variation exists within a population. Mutations can introduce new alleles, which might or might not give improved functionality as compared to the preexisting ones. Random assortment and crossing over create new combinations of alleles of different genes.

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.

The hamsters with larger wings are strong enough to make it to a 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.

He reasoned that populations rather than individuals evolved. This evolution is possible because genetic variation already exists within a population. Individuals with different genotypes in the population survive and reproduce at different rates. The agent that determines a differential rate of reproduction is called natural selection.

Lamarckism vs. Darwinism

Note the difference between Darwin's and Lamarck's theories. Lamarck believed that the need for a new trait would promote the evolution of that trait. Darwin proposed that evolution occurred through the selective pressure for a preexisting trait in a population. Both theories seem kind of reasonable, so how do we determine which theory most accurately describes what is going on in nature?

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