Natural Selection Flashcards
Who was the co-discoverer of natural selection (along with Darwin)?
Alfred Russel Wallace
What is artificial selection? What do we mean by “artificial”?
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.
Why was Darwin interested in pigeons?
Darwin saw pigeons as a prime example of how artificial selection can drastically alter traits within a single species.
Know the three steps to Natural Selection presented in class. Why is it “natural”?
- Individuals vary in phenotype
- Some of this phenotypic variation is heritable
- The variable, heritable traits affect an individual’s probability of leaving offspring.
Why is Darwin’s “struggle for existence” important for natural selection?
Not all individuals survive to reproduce, or reproduce maximally. There is a struggle for existence, leading to variability in reproductive output.
What is the consequence of natural selection?
Traits which increase an organism’s chance of survival and reproduction become more prevalent in a population over time
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?
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.
Does natural selection operate directly on phenotypes or genes?
It operates directly on phenotypes.
Why is it that to understand natural selection, one must think in terms of probabilities?
Traits under natural selection only impact the probability of survival and reproduction
Is natural selection testable?
Yes it is testable
Why is Peter & Rosemary Grant’s work on Darwin’s finches an excellent example of evolution by natural selection? What trait evolved?
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).
What evidence was used to show that beak depth is heritable?
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
What evolves: individuals or populations?
Populations
What is a histogram?
the most commonly used graph to show frequency distributions
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?
The direction of selection depends on ecology.
What does it mean to say that Natural Selection is non-random (systematic, in fact), but not necessarily progressive?
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
What is wrong with this: Fishes wanted to get onto land, so they evolved limbs.
It implies that evolution is driven by conscious desire or intent. Also, evolution is a “tinkerer” not an engineer. Tinkering proceeds step-by-step.
What is teleology?
the explanation of phenomena in terms of the purpose they serve rather than of the cause by which they arise.
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
A
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?
No, if allele frequency isn’t changed. Natural selection without evolution can occur though.
Using the tinkerer analogy, explain why it is that Natural Selection may not always lead to perfection. Compare and contrast local vs. global optima.
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
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.”
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!)
