Natural Selection (Lecture 4)

A set of Question-and-Answer flashcards covering natural selection, evolution, Darwin’s observations and inferences, artificial selection, and common misconceptions.

What is natural selection?

A process where individuals with favorable inherited traits are more likely to survive and reproduce, leading to a higher frequency of those traits in a population and the elimination of maladaptive traits; it is the mechanism that leads to evolution.

How is evolution different from natural selection?

Evolution is the change observed in populations over time; natural selection is the mechanism that produces that change. Natural selection changes the average traits in a population across generations, and individuals do not evolve.

What three components together yield natural selection (per the notes)?

Variation, differential reproduction, and heredity (inherited variation).

What does fitness mean in this context?

Fitness equals survival plus reproduction.

Do individuals evolve according to the notes?

No. Individuals do not evolve; populations do. The average traits in a population can change over generations.

What does the ‘average’ change in a population illustrate?

The population average changes due to differential survival and reproduction, not because individuals change during their lifetimes.

What are Darwin’s five observations summarized in the notes?

1) All species can produce more offspring than the environment can support; 2) Natural populations remain relatively constant in size; 3) Resources are limited; 4) Members of a population vary in their traits; 5) Much of this variation is heritable.

Observation #1 in Darwin’s observations

All species can produce more offspring than the environment can support.

Observation #2 in Darwin’s observations

Natural populations remain relatively constant in size.

Observation #3 in Darwin’s observations

Resources are limited.

Observation #4 in Darwin’s observations

Members of a population vary in their traits.

Observation #5 in Darwin’s observations

Much of this variation is heritable.

What are Darwin’s inferences #1, #2, and #3?

1) Overproduction with limited resources leads to a struggle for existence; only a portion of offspring survive. 2) Survival is not random; it depends on hereditary traits, leading to natural selection. 3) Over generations, natural selection leads to evolution and sometimes new species.

What is the artificial selection discussed in the notes?

Humans modifying species by selecting and breeding individuals with desired traits.

Give examples of artificial selection in Brassica species shown in the notes.

Brussels sprouts, Kale, Cabbage, Broccoli, Wild mustard, Kohlrabi.

What is the key takeaway about artificial vs natural selection and descendant variety?

If humans can produce very different descendants through artificial selection, natural selection can do the same, just over a longer time.

How is natural selection described as a sieve?

Natural selection acts like a sieve, favoring individuals with traits favorable to a given environment; it has no goals or objectives.

What is a common Lamarckian claim that Darwin argued against?

That individuals acquire traits during their lifetime and pass those acquired traits to offspring; in contrast, populations evolve, not individuals, and acquired traits are not inherited.

Why did long necks evolve in giraffes, according to the notes?

Mutations that lengthened necks arose; natural selection favored longer necks over generations; evolution proceeded because those variants survived and reproduced.

What does the phrase “Good enough is good enough” imply in evolution?

Evolution often produces workable solutions rather than perfect designs; mutations that work well enough to improve survival can be selected over time.

What is the role of variation being heritable in natural selection?

Heritable variation allows traits to be passed to offspring, enabling differential survival and reproduction to shift trait frequencies across generations.

What does Darwin’s Inference #2 state about survival?

Survival in the struggle for existence is not random but depends on the hereditary constitution of individuals, which is natural selection.

What does Inference #3 say about generations and evolution?

Over generations, natural selection leads to a continuing gradual change in populations, potentially producing new species.

What is the main takeaway of Darwin’s logic as presented in these notes?

All species have high reproductive potential, resources are limited, variation exists and is heritable, and natural selection acts on this variation to change populations over time.