Reading Assignment: Why We Get Sick: The New Science of Darwinian Medicine, pp.13-25.
 

CHAPTER 2: EVOLUTION BY NATURAL SELECTION:

How do Nesse & Williams explain the process of natural selection?

"The process is fundamentally very simple: natural selection occurs whenever genetically influenced variation among individuals affects their survival and reproduction. If a gene codes for characteristics that result in fewer viable offspring in future generations, that gene is gradually eliminated. For instance, genetic mutations that increase vulnerability to infection, or cause foolish risk taking or lack of interest in sex, will never become common. On the other hand, genes that cause resistance to infection, appropriate risk taking, and success in choosing fertile mates are likely to spread in the gene pool, even if they have substantial costs." (My italics)
 

Does the British moth example illustrate natural selection?

Yes, the rare mutant form of moth (its darker color better matched color of pollution-coated trees, making it harder for birds to detect them) spread quickly.
 

Does Herbert Spencer's catchy phrase "survival of the fittest" capture the essence of evolution

by natural selection? If not, what misunderstandings does it promote?

Not at all. Survival is of no consequence per se, e.g., consider salmon and annual plants that

reproduce once and then die. Survival increases fitness only so far as it increases reproduction. 'Fittest' does not mean healthiest, strongest, fastest, etc. Roughly, those with the most grandchildren are the fittest. Fitness is not absolute but is relative to environments. Even in a particular environment, every gene involves compromises, e.g., fearfulness in rabbits.
 

NATURAL SELECTION BENEFITS GENES, NOT GROUPS:

Is group selection exemplified by lemmings engaging in mass suicide when food is scarce?

No, this is a hokey example cooked up by a TV company. Lemmings seldom drown or fall victim to mass accidental death en masse. Consider two imaginary lemmings, one with self-

sacrificial genes, the other without them. Which one would likely have the most grandchildren?
 

Can group selection ever occur?

Yes, but only under very special and rare circumstances.
 

How does Richard Dawkins's characterization of organisms as vehicles created by genes in

order to replicate themselves fit in with ideas that evolution tends toward a world of health,

harmony, stability, and happiness? How apt is Dawkins's moniker "selfish genes"?

It shows how misguided these ideas are. What promotes reproductive success will be selected for, irrespective of how it affects individuals. Dawkins's term nicely emphasizes that genes have no concern for their vehicles as such, but it causes many people to attribute intentionality to genes.
 

KIN SELECTION:

Does reproduction by a carrier organism or vehicle enable a gene to get more copies of itself into

future generations? Always?

Usually, but it depends on the environment, on historical accident, etc.
 

Suppose that the carrier organism performs actions that increase the reproductive success of

its close relatives. Does this circumstance also enable a gene to get more copies of itself into

future generations?

Probably yes, because a child shares all of its genes with an identical twin; [3/4 of its genes with a half-identical twin] 1/2 with a sibling; 1/2 with a parent; 1/4 with a grandparent; and 1/8 with a cousin. From the perspective of your genes, your brother's survival is half as important as yours, etc.
 

Why is it called "kin selection"? Explain J.B.S. Haldane's quip that he'd sacrifice his life for

two brothers or eight first cousins, but not for one brother or seven cousins?

Because it is kin with whom we share a significant fraction of genes. Two brothers have same significance for a person's genes as does the person himself, etc.
 

Is kin selection the only exception to the "Nice-guys-finish-last" principle (formulated by Leo Durocher, manager of the old Brooklyn Dodgers)?

No, there is also reciprocal exchanges or reciprocity.
 

What is reciprocity? Does reciprocity amount to mutual backscratching? Explain how reciprocal behavior by the carrier organism enables a gene to get more copies of itself into future generations. What bearing do kin selection and reciprocity have on social behavior and the possibility of altruism?

Reciprocity is mutual favor-granting, positive tit for tat, mutual backscratching. It helps an individual to survive to reproduce and to promote the well-being of offspring. It enables biologists/ethologists to account for altruism, which would otherwise be baffling from an evolutionary point of view.
 

HOW DOES NATURAL SELECTION OPERATE?

Does natural selection proceed according to some overall plan or scheme? In some particular direction, e.g., toward better or higher beings?

No, no goal or plan apart from fostering reproductive success.
 

Is it predictable? If not, is the theory of natural selection untestable?

Although the course of natural selection is not generally predictable, natural selection leads to many predictions, and so is empirically testable.
 

In what five ways does chance influence natural selection?

(1) In the production of a genetic mutation; (2) in whether the bearer lives long enough to show the effects of such a mutation; (3) in chance events that influence the bearer's reproductive success; (4) in whether a gene happens to be eliminated by accident; and (5) in unpredictable changes in the environment of the group of organisms that the bearer is a member of.
 

If one rewound and then replayed the tape of biological history, would one see the same show? Would there be humans in the replay?

The probability of seeing the same show is zero. Similarly for humans.
 

Does natural selection always do what is best for the long-term welfare of a species? Does it create every adaptation that would be valuable to a species?

Natural selection would do what is best for the long-term welfare of a species only if it operated at the group level, which it almost never does. Nor does natural selection create every adaptation that would be valuable to a species, as is shown by African monkeys who lack tails, which their South American counterparts find quite valuable.
 

Explain how natural selection approaches perfection by optimizing certain quantitative features of organisms? Give some animal and human examples.

If a quantitative trait serves a definite function, selection among minor modifications results over many generations in an optimal, or nearly optimal, value of the trait. Examples: the length of a birds' wings is long enough to provide good lift but short enough for the bird to maintain control; our

blood pressure is optimal, neither too high nor too low.
 

What is the point of the story about Henry Ford and the steering column of his Model T's? What's the connection between costs and benefits?

Henry Ford recognized that engineering decisions are based on cost-benefit analyses. A steering column that never breaks down probably has an inordinately high cost. By modestly disimproving the steering column, the engineer could save the Ford company a lot of money without significantly disimproving the hypothetical Model T.
 

Does natural selection ever compromise, i.e., does it ever make decisions based on cost-benefit analyses? Give some animal and human examples.

Virtually all the 'decisions" made by natural selection are compromises. Example: the fear instinct of horses is strong enough to enable them almost always to escape predators, but not so strong as to make their lives impossible.
 

Are some apparent design mistakes really positive benefits to an organism? Give examples?

A classic example is the gene for sickle cell anemia, which protects against malaria. Another

example: our fondness for fat promotes survival in a central-African hunter-gatherer environment.
 

TESTING EVOLUTIONARY HYPOTHESES:

Aristotle, the father of functional analysis (What is it for?), stated that the body as a whole

has a special purpose or function. What do Nesse & Williams take that purpose or function

to be?

Reproduction!
 

What does it mean to say that a biological trait or behavior is "adaptive"? Give animal and

human examples. Can one test hypotheses about the adaptiveness of traits or behaviors?

It is adaptive if it promotes reproductive success. E.g., ears enable humans and animals to

detect the approach of predators, to communicate over distances, etc., all of which enable the

individual to reproduce and get its genes into the next couple of generations.
 

Mention some adaptational hypotheses that are superficially attractive but empirically false.

Mention some adaptation hypotheses that are obviously true.

False hypotheses: infants cry to exercise their lungs; people die by age 100 to make room for

new people. True hypotheses: the heart pumps blood to nourish the cells of the body; coughing

expels foreign matter from the respiratory tract; shivering increases body heat.
 

Which adaptational hypotheses do Nesse & Williams view as "interesting"?

Ones that are plausible and important, but that are not obviously right or wrong.
 

THE ADAPTATIONIST PROGRAM:

What is the method of inquiry known as "the adaptationist program"?

Make an educated guess at the functional significance of some known trait or behavior (a functional hypothesis); then form a testable prediction by tracing the consequences of that hypothesis; then test the prediction. If it holds good, we may be on to something; if it proves false, then discard

the functional hypothesis.
 

Does it ever lead to novel predictions? To empirically testable knowledge?

Yes to both. The three following cases are examples of empirically testable predictions made from functional hypotheses that lead to new knowledge.
 

Explain the significance of Nesse & Williams three examples: (1)How beavers decide which trees to fell; (2) How woodland songbirds decide how many eggs to lay; and (3) How woodland songbirds determine the male-female ratio of their offspring.

Gary Belovsky conjectured that beavers decide which trees to cut down in a way that promotes fitness, i.e., in an economically rational way. This functional hypothesis lead to the prediction that the caliper of trees harvested by beavers decreases with distance from their pond, and that at some definite distance only ideal trees would be cut down, and beyond that distance, no trees would be felled.
 

How do adaptationists explain the 50-50 sex ratio of humans and other sexual animals? What does it have to do with the genetic fact that an individual has an equal chance of getting an X or a Y chromosome from its father?

The minority sex has the advantage in mating, so natural selection over time would produce a 50-50 sex ratio. The chromosomal facts are the proximate mechanism by which the result of natural selection is accomplished.
 

What bearing do Nesse & Williams think the adaptationist program has for the investigation of disease, illness, and physiological disorders? Do they expect it to lead to important medical discoveries?

They expect it to lead to important medical discoveries, just as it has led to important discoveries in ethology.
 

Can a trait or behavior have more than one function or purpose? Give animal and human examples.

Yes, e.g., the tongue plays a role in speech and in eating.
 

What experimental limitations does the adaptationist program encounter?

There is no way to experiment on the hypothesized evolutionary history of an organism.
 

If we cannot reconstruct the history of a trait or behavior, how can we be confident that it

was shaped by natural selection?

Fossils, carbon traces, behavioral tendencies, protein and DNA structures, etc., all help us to reconstruct evolutionary history. Comparative physiology can help to determine the function of a trait or behavior.
 

How many of the evolutionary (adaptationist) hypotheses advanced in their book do Nesse & Williams consider to be tested and confirmed? What is their goal or objective?

They claim confirmation for none of them. They want to demonstrate that evolutionary questions are interesting, important, and testable. They hope to cause people to ask new questions.