3. Behavioral Evolution II

TL;DR

Three building blocks explain the evolution of behavior: individual selection (passing on your own genes), kin selection (helping relatives in proportion to shared genes, so you would lay down your life for two full siblings or eight cousins), and reciprocal altruism (cooperation between unrelated individuals). Knowing only whether a species is tournament or pair-bonded predicts aggression, body-size differences, parenting, and mate choice.

Transcript

[MUSIC PLAYING] Stanford University. OK. Let's get going. Various announcements, procedural things. A number of people want more information about grading and what the exams are like, all of that. I think I mentioned one-third of the points will come from the midterm, 2/3 from the final. In terms of the style of the midterm, the midterm is heavily... Read More

Key Insights

• Individual selection is the first building block of behavioral evolution: an organism passes on as many copies of its own genes as possible through its own reproduction, which makes behavior an epiphenomenon in service of getting another copy of the genes into the next generation.
• Kin selection works by Mendelian arithmetic: you share half your genes with a full sibling and a quarter with a half sibling, so the logic predicts you would gladly lay down your life for one identical twin, two full siblings, or eight cousins.
• Social animals across the galaxy are obsessed with kinship because cooperative behaviors play out along lines of relatedness, which determines who counts as an "us" and who counts as a "them."
• Reciprocal altruism is the third building block, and it shows that cooperation does not require relatedness. You scratch my back, I'll scratch yours, formalized by game theorists working out when to cooperate and when to defect.
• The prisoner's dilemma is the building block of the entire field of game theory, with strategies worked out by mathematicians, economists, and diplomats, and real animals in the wild have evolved optimization strategies for when to cooperate and when to defect.
• In tournament species, males are dramatically un-choosy about mates because the only cost involved is the cost of sperm and no parental behavior, and reproductive variability is extreme, with 5% of males accounting for 95% of matings.
• Female choice in tournament species targets good genes alone, since no fatherhood is forthcoming from the male, which drives a corresponding world of males across the animal kingdom faking markers suggesting better genes than they actually have.
• Pair-bonded species show low aggression, small differences in body size, secondary sexual characteristics, and lifespan, because males are selected to be as close to females as a male can be, and females select for competent fatherhood rather than genes alone.

Questions & Answers

Q: What are the three building blocks for understanding the evolution of behavior?

The three building blocks are individual selection, kin selection, and reciprocal altruism. Individual selection means passing on as many copies of your own genes as possible through your own reproduction. Kin selection means that sometimes the best way to increase the number of genes you pass on is to help relatives reproduce, constrained by the mathematical logic of how related you are. Reciprocal altruism means cooperation between individuals who need not be related at all, captured by the phrase "you scratch my back, I'll scratch yours."

Q: How many relatives would you lay down your life for under kin selection logic?

Under the mathematical logic of Mendelian relatedness, you would gladly lay down your life for one identical twin, two full siblings, or eight cousins. This follows from the fact that you share half your genes with a full sibling and a quarter with a half sibling. The point is that the calculation is constrained by a vicious mathematical logic in which the value of the sacrifice depends entirely on how related you are to the relative you are helping, since the currency being maximized is copies of genes reaching the next generation.

Q: What is a tournament species and what traits does it predict?

A tournament species is one with high levels of aggression among males and male-male competition for access to females. Because males are selected for muscle mass, secondary sexual characteristics, plumage, and big sharp canines for slashing the other guy, males tend to be a lot bigger than females. Tournament species also show single births, low levels of male parenting, no female abandonment of offspring since nobody else would care for them, extreme variability in male reproductive success, and males living a lot shorter than females.

Q: Why are males in tournament species un-choosy about who they mate with?

In tournament species, males will mate with anyone who will mate with them because there is essentially no cost involved. There is no parental behavior required of them, so the only thing invested is the cost of sperm. Researchers have literally analyzed the relative cost of sperm versus eggs in tournament species. Because the investment asymmetry is so large, males are dramatically un-choosy while females, who bear the full cost of offspring, become highly selective.

Q: What do females look for in a mate in tournament species versus pair-bonded species?

In a tournament species, a female is certainly not going to get good fatherhood out of the male, so all she can hope for is good genes. This produces a whole world of female selectivity for markers of good genes, and a corresponding world of males across the animal kingdom trying to fake out females by suggesting they have better genes than they actually do. In pair-bonded species, a female wants someone who is going to be a competent father, which is why males in those species court with rituals such as bringing food.

Q: How do pair-bonded species differ from tournament species?

Pair-bonded species present a completely different picture. Males are careful about who they mate with because the wiring is that you mate and then you take care of the kids. Male parenting levels are high, which lets females abandon offspring and have multiple births. Males are selected to be as close to females as a male can be, so there is no big difference in body size, no big difference in secondary sexual characteristics, no high level of aggression, and no big difference in lifespan between the sexes.

Q: Why is behavior treated the same way as organs like hearts and kidneys in evolutionary biology?

There is an un-fightable logic to why hearts have to be the size they are and kidneys have the filtration rates they have, namely that these features solve the challenge of leaving as many copies of your genes in the next generation as possible. Making sense of hearts and kidneys can be the work of bioengineers and biomechanics researchers operating under that underlying logic. The rationale for applying the same reasoning to behavior is that behavioral strategies can be optimized just as you can optimize how long a giraffe's neck should be.

Q: What can you infer about a species from just a male and a female skull?

Knowing nothing more than that one skull is an adult female and the other an adult male, you can work through the logic of individual selection, kin selection, and reciprocal altruism and infer a great deal about the private lives of that species. The size difference and the presence or absence of features such as large canines tell you whether the species is tournament or pair-bonded, which in turn predicts aggression levels, parenting patterns, mate choice, birth patterns, and lifespan differences between the sexes.

Summary

In this video, the speaker discusses various announcements and procedural details for a course. They go on to explain the style of exams, required readings, and the length of each lecture topic. The speaker also covers topics like evolution, behavior genetics, and reciprocal altruism. They explore the concept of infanticide and its implications for reproductive success. The speaker then applies evolutionary principles to understand social behavior in animal species. They discuss dominance hierarchies, sex ratios, and polyandry.

Questions & Answers

Q: What is the midterm focused on?

The midterm mainly tests your knowledge of the factoids from the first half of the course. It ensures that you have a solid understanding of the basics of each topic covered.

Q: What is the style of the final exam?

The second half of the final exam is focused on integration and thinking across different categories. It requires you to apply your knowledge to connect different concepts.

Q: What chapters of the required books should be read?

The chapters from the required books are not necessary for the first half of the course. The reading handout will specify the chapters from the [? Zebra ?] book, and the chapters from the [? Chaos ?] book will be provided shortly.

Q: Are the readings being posted on CourseWorks necessary to read in detail?

It depends on the paper. Some papers may require a full reading, while others may only need an abstract. The goal is to be able to summarize the paper and understand its relevance to the topic it falls under.

Q: When should the readings be completed?

It is recommended to read the assigned papers after the first lecture of each topic. This way, you can better grasp the context and relevance of the papers.

Q: How long will each lecture topic last?

The duration of each lecture topic varies. For example, the evolution lecture topic will cover two classes, while the molecular genetics topic may take one to one and a half classes. It is important to stay on schedule to cover all the material.

Q: When is the midterm scheduled?

The midterm is scheduled for a Monday night. You will be responsible for material up to the previous Wednesday. Review material will be provided to help you prepare.

Q: What should I expect during the week devoted to intro to the topics?

The week devoted to intro to the topics is crucial for everyone to be up to speed. It will be taught by the TAs. The following week will have more advanced lectures, and there may be a half-lecture on statistics based on the proximity to the midterm.

Q: What are the main takeaways from the lectures on evolution and behavior genetics?

The lectures on evolution and behavior genetics explore various concepts and principles. They discuss the logic behind the evolution of certain behaviors, the significance of individual selection, kin selection, and reciprocal altruism. They also address questions related to the evolution of cooperation and infanticide.

Q: Can we infer the social behavior of a species based on individual factoids?

Yes, once you have a basic understanding of individual selection, kin selection, and reciprocal altruism, you can logically infer the social behavior of a species. By analyzing characteristics like gender differences, aggression levels, and parental behavior, you can make accurate predictions about the species' social dynamics.

Q: How do animals behave in terms of killing and offspring protection?

Animals do not always behave for the good of the species or group. The speaker mentions examples of infanticide in various species, which challenges the idea of nature being benign. They explain that infanticide can be a competitive strategy to reduce the reproductive success of other males. They also discuss the role of kinship, maternal defense, and pseudo-estrus in protecting offspring.

Takeaways

The lectures covered in this video provide insights into various topics related to evolution, behavior genetics, and social behavior in animal species. The principles of individual selection, kin selection, and reciprocal altruism help explain various behaviors observed in nature. The lectures emphasize the importance of understanding these principles in order to make logical inferences about social dynamics and reproductive strategies. Additionally, the examples of infanticide challenge the notion of animals always behaving for the good of the species, highlighting the complexity and varied strategies in nature.

Summary & Key Takeaways

• The lecture opens by discarding three popular misconceptions covered earlier: that Darwin invented evolution, that "survival of the fittest" captures the mechanism, and that animals behave for the good of the species. Group selection arguments are rejected. What replaces them is a logic in which every organ and every behavior is judged by how many copies of your genes reach the next generation.

• The same engineering logic that explains why hearts are a certain size and kidneys have particular filtration rates applies to behavior. Just as a bioengineer can ask how long a giraffe's neck should be, a behavioral biologist can ask which behavioral strategies are optimal. No animal, with the possible exception of some other apes, consciously strategizes; personifying the organism is only a convenience for teaching.

• Three building blocks structure the field. Individual selection: a chicken is an egg's way to make another egg, and behavior is an epiphenomenon serving gene transmission. Kin selection: helping relatives reproduce, constrained by Mendelian relatedness (half your genes with a full sibling, a quarter with a half sibling). Reciprocal altruism: cooperation among non-relatives, formalized through game theory and the prisoner's dilemma.

• Tournament species show high male-male aggression over access to females, so males are larger, carry secondary sexual characteristics such as plumage and large slashing canines, and are dramatically un-choosy about mates because the only cost is sperm. Reproductive success is highly skewed, with 5% of males accounting for 95% of the matings, and females select for markers of good genes alone.

• Pair-bonded species invert the picture. Males mate carefully because mating comes wired to parenting, so male parental investment is high and females can abandon offspring and have multiple births. Selection pushes males to resemble females, so size differences, secondary sexual characteristics, aggression levels, and lifespan gaps all shrink. Females choose competent fathers, and males court by bringing food and similar rituals.

• The course structure was also outlined: one-third of points from the midterm and two-thirds from the final, with the midterm testing factoids from each conceptual bucket and the second half of the final testing integration across categories. Molecular genetics, behavior genetics, ethology, neurobiology, and endocrinology follow, and the midterm falls on a Monday night.