Natural Selection

Question 1

Who was the co-discoverer of natural selection (along with Darwin)?

Answer 1

Alfred Russel Wallace

Question 2

What is artificial selection? What do we mean by “artificial”?

Answer 2

The process where humans intentionally select specific traits or animals to breed and pass onto future generations. “Artificial” means the selection is not coming from the environment it is coming from humans.

Question 3

Why was Darwin interested in pigeons?

Answer 3

Darwin saw pigeons as a prime example of how artificial selection can drastically alter traits within a single species.

Question 4

Know the three steps to Natural Selection presented in class. Why is it “natural”?

Answer 4

1. Individuals vary in phenotype
2. Some of this phenotypic variation is heritable
3. The variable, heritable traits affect an individual’s probability of leaving offspring.

Question 5

Why is Darwin’s “struggle for existence” important for natural selection?

Answer 5

Not all individuals survive to reproduce, or reproduce maximally. There is a struggle for existence, leading to variability in reproductive output.

Question 6

What is the consequence of natural selection?

Answer 6

Traits which increase an organism’s chance of survival and reproduction become more prevalent in a population over time

Question 7

If a population exhibits variation in a character, can natural selection act on that
character? If the variation character is not variable due to heritable genetic factors,
can it evolve through natural selection?

Answer 7

Yes, natural selection can only act on a character within a population if there is variation. The character cannot evolve through natural selection if it is not variable due to heritable genetic factors.

Question 8

Does natural selection operate directly on phenotypes or genes?

Answer 8

It operates directly on phenotypes.

Question 9

Why is it that to understand natural selection, one must think in terms of probabilities?

Answer 9

Traits under natural selection only impact the probability of survival and reproduction

Question 10

Is natural selection testable?

Answer 10

Yes it is testable

Question 11

Why is Peter & Rosemary Grant’s work on Darwin’s finches an excellent example of evolution by natural selection? What trait evolved?

Answer 11

They were able to directly observe, over multiple generations, how the beak size of the finches changed in response to environmental pressures (like droughts in 1977 and 2004).

Question 12

What evidence was used to show that beak depth is heritable?

Answer 12

Peter and Rosemary Grant created a graph showing the strong correlation between parent finches and their offspring’s beak depth. The offspring of surviving medium-ground finch individuals had beaks similar in size to those of their parents

Question 13

What evolves: individuals or populations?

Answer 13

Populations

Question 14

What is a histogram?

Answer 14

the most commonly used graph to show frequency distributions

Question 15

In 1977, a drought resulted in the selection of deeper beaks. In 2004, a drought resulted in selection for narrower beaks, due to the presence of another species that was not there in 1977. What does this say about the nature of natural selection?

Answer 15

The direction of selection depends on ecology.

Question 16

What does it mean to say that Natural Selection is non-random (systematic, in fact), but not necessarily progressive?

Answer 16

while the initial genetic variations within a population may occur randomly through mutation, the process of selection itself is not random, it is leading to a better mutation for the environment. It is not progressive because there is no predetermined goal in natural selection

Question 17

What is wrong with this: Fishes wanted to get onto land, so they evolved limbs.

Answer 17

It implies that evolution is driven by conscious desire or intent. Also, evolution is a “tinkerer” not an engineer. Tinkering proceeds step-by-step.

Question 18

What is teleology?

Answer 18

the explanation of phenomena in terms of the purpose they serve rather than of the cause by which they arise.

Question 19

Pick either A or B: populations reflect (A) the impacts of natural selection in the previous generation, or (B) the needs of the population in the next generation

Answer 19

A

Question 20

If Natural Selection acts on phenotypes in a population, but the frequency of alleles in
the next generation has not been altered, has evolution occurred? Why might this
happen?

Answer 20

No, if allele frequency isn’t changed. Natural selection without evolution can occur though.

Question 21

Using the tinkerer analogy, explain why it is that Natural Selection may not always lead to perfection. Compare and contrast local vs. global optima.

Answer 21

Natural selection is limited to tinkering with existing variations, leading to local optima (the population has reached a point where further changes would be detrimental to their survival in the current environment), not always reaching the theoretical “global optimum”( theoretical “best possible” adaptation for a given environment) that could exist in an idealized scenario

Question 22

What is wrong with this statement: “The female decided not to breed last year, because resources were scarce and it would have been bad for the species.”

Answer 22

An adaptation must evolve by increasing the reproductive output of its possessor. Reproduction, not survival, determines which genes make it to the next generation. A gene that benefits reproduction at a young age, yet leads to undesirable things can be favored by natural selection. Natural selection never favors the trait “for the good of the species,” as it can only act on individuals and proceeds without foresight (no teleology!)