3. Behavioral Evolution II
Stanford・74 minutes read
Evolutionary principles predict animal behaviors like infanticide and mating strategies. Imprinted genes show intersexual competition and varied reproductive strategies in species.
Insights
- Grading in the course heavily relies on the final exam, which focuses more on integration than the midterm, which tests course factoids.
- Required readings are not essential until the second half of the course, with specific chapters from Zebra and Chaos books to be announced; readings on CourseWorks are mandatory.
- Understanding the relevance of readings is more crucial than memorizing details; wait until after lectures to read for better comprehension.
- Evolutionary principles can accurately predict social behaviors in various species, revealing mating strategies, parenting roles, and social dynamics.
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Recent questions
What is the breakdown of grades in the course?
1/3 from midterm, 2/3 from final.
When are required readings necessary in the course?
Second half of the course.
How should readings be approached in the course?
For relevance, not memorization.
What is the schedule for lectures in the course?
Evolution spans two classes.
What are the key building blocks of evolutionary behavior principles?
Individual selection, kin selection, reciprocal altruism.
Related videos
Summary
00:00
Evolutionary Behavior Principles and Predictability in Species
- Grading breakdown: 1/3 of points from midterm, 2/3 from final; midterm focuses on course factoids, final on integration.
- Required readings: Books not needed until second half of course; specific chapters from Zebra and Chaos books to be announced; CourseWorks posted readings are mandatory.
- Reading approach: Readings should be understood for relevance, not memorized in detail; wait until after lectures to read.
- Lecture schedule: Evolution topic spans two classes; Molecular genetics, Behavior genetics, Ethology, Neurobiology, Endocrinology each get one to one and a half classes.
- Midterm details: Scheduled for a Monday night; material up to previous Wednesday is covered; review materials will be provided.
- Evolutionary behavior principles: Individual selection, kin selection, reciprocal altruism are key building blocks.
- Tournament species behavior: Males compete aggressively for females, leading to male size differences, high aggression, and low parenting.
- Pair-bonded species behavior: Males invest in parenting, females can abandon offspring, leading to equal male-female size, low aggression, and high parenting.
- Predictability through principles: Applying evolutionary principles can predict social behaviors in different species accurately.
- Animal behavior examples: Applying principles reveals mating strategies, parenting roles, and social dynamics in various species.
13:08
Evolutionary strategies behind animal infanticide behaviors
- Babies are perceived as cute and evoke caregiving instincts in humans.
- Initially, the belief was that baby features reduce aggression, but field biologists observed infanticide in various species.
- Infanticide, primarily by adult males, is a competitive strategy to decrease the reproductive success of other males.
- In species with competitive infanticide, males target infants most likely to be sired by other males.
- Competitive infanticide occurs when the average interbirth interval among females exceeds the tenure of high-ranking males.
- Females in some species induce miscarriages when a new male threatens their offspring, maximizing their reproductive success.
- Older females and grandmothers in langur monkeys defend offspring more vigorously, prioritizing genetic propagation.
- Pregnant females in some primate species enter pseudo-estrus to deter infanticide by new males, deceiving them into mating.
- Evolutionary pressures may favor males who do not recognize their offspring, as impulsive mating behaviors prevail.
- The behavior of animals, including infanticide, often reflects evolutionary strategies rather than conscious cognitive decisions.
26:13
Male Baboons' Strategic Offspring Selection for Protection
- Males may not have evolved to understand the connection between mating and offspring, lacking cognitive ability in this area.
- Studies on baboons in the 1960s revealed a male's use of infants to avoid aggression from dominant males.
- Males strategically choose which infant to grab, often selecting their own offspring to protect against aggression.
- High-ranking males with more offspring are less likely to have their children kidnapped by lower-ranking males.
- Male baboons have been observed consciously selecting the offspring of other males to use as leverage in conflicts.
- Dominance hierarchies among female primates are based on nepotism, with daughters inheriting their mother's rank.
- The decision to have male or female offspring is influenced by the reproductive costs and probabilities associated with each gender.
- In species with high male reproductive variability, having sons is a riskier strategy compared to daughters.
- Ecological pressures can influence the sex ratio of offspring, with females being favored during times of scarcity.
- Adelphic polyandry, where a female mates with multiple males, often involves brothers sharing breeding rights, seen in species like lions and occasionally in humans.
39:03
"Imprinted genes and intersexual competition in species"
- In traditional Tibetan society, adelphic polyandry is practiced, where a woman marries a man along with all his brothers to prevent land inheritance splitting.
- Adelphic polyandry is seen in agriculturally impoverished areas to maintain land unity among brothers.
- Intersexual competition is observed in species where males and females have different reproductive interests.
- Imprinted genes, which work differently depending on the parent they come from, were discovered in the early 1990s.
- Imprinted genes from fathers promote fetal growth, while those from mothers tend to slow it down, showcasing intersexual competition.
- Imprinted genes can affect fetal development and placental invasion, leading to diseases like choriocarcinoma.
- Imprinted genes also influence post-birth behaviors, such as suckling reflexes, showing the ongoing competition between males and females.
- Imprinted genes are prevalent in tournament species but not in pair-bonding species like voles.
- Humans exhibit imprinted genes, indicating a mix of tournament and pair-bonding species traits.
- Homosexuality and the complexity of intersexual competition will be further discussed in a future lecture.
52:37
Sperm competition and evolution in animal reproduction.
- Females in the animal kingdom have sperm from multiple males inside them due to mating frequency.
- Sperm competition is a field of research where sperm from different males compete.
- Male fly species produce toxins in their sperm to kill the sperm of other males.
- These toxins can harm female health, shortening their life expectancies.
- Male sperm evolve to become more toxic, affecting female reproductive success.
- Females evolve ways to detoxify male sperm over generations.
- In social primates, either females or males disperse to avoid inbreeding.
- In species where males disperse, there is higher male-male aggression within groups.
- Group selection can occur when a subset of a population becomes isolated and more inbred.
- Inbred populations can drive cooperation through kin selection and founder effects.
01:05:49
Cooperation and Group Selection in Evolutionary Biology
- People related to each other engage in cooperative and kin-selective behavior, such as making low-interest loans to each other.
- This cooperative behavior leads to increased success in business and incorporation into a group, creating an economic force that others feel compelled to join.
- The concept of group selection is explored, where cooperation and kin selection drive initial cooperation, leading to the crystallization of cooperative traits in the population.
- Initiating cooperation in a world without reciprocal altruism is challenging, as someone must make the first move towards cooperation.
- Group selection can lead to the dominance of certain traits within a group, even if they are disadvantageous individually.
- Evolutionary biologists like David Sloan Wilson have studied the role of group selection in the formation and success of religious groups like Calvinism.
- Multi-level selection is a crucial concept, highlighting how selection can occur at the gene, individual, or group level.
- The reconciliation between individual selectionists and group selectionists like David Sloan Wilson and EO Wilson has led to a new understanding of how selection operates at different levels.
- Applying evolutionary models from other species to humans must be done cautiously, as humans possess unique traits and behaviors that may not fit neatly into these models.
- Criticisms of the framework that social behavior is solely driven by kin selection and group selection include questions about the heritability, adaptiveness, and gradual nature of behavioral traits.
01:19:14
Genetic Influence and Evolutionary Change in Behavior
- The phrase "when a behavior is genetic" is misleading and should be reframed as "how to determine if a behavioral trait has a genetic influence."
- Sociobiological thinking involves an inverse style of proof to determine genetic influence in behaviors, focusing on heritability and adaptiveness.
- The adaptationist fallacy criticizes the belief that all traits evolve for a specific adaptive purpose, leading to the creation of "just-so stories" to explain traits.
- Some traits may not have evolved due to adaptiveness but rather as spandrels, unintended outcomes of other selected traits.
- Spandrels are traits that occur as a byproduct of other selected traits, not necessarily for adaptive reasons.
- Evolution is described as tinkering with preexisting structures, leading to the presence of spandrels in various traits.
- Evolution is not solely driven by competition, as emphasized by evolutionary biologists from the Soviet Union who focused on surviving environmental extremes.
- The concept of gradualism in evolution, where every advantage is worth fighting for, is challenged by the idea of punctuated equilibrium, suggesting long periods of stability followed by rapid evolutionary change.
- Punctuated equilibrium proposes that evolution occurs in sudden bursts of change rather than gradual, incremental steps.
- Molecular genetics align better with models of punctuated equilibrium and stasis, challenging the traditional gradualist view of evolution.
01:31:34
"Evolution: Punctuated Equilibrium and Sociopolitical Implications"
- Evolution is not a constant process of competition; rather, it involves periods of severe selection followed by long periods of inactivity.
- The punctuated equilibrium model is emphasized as a more fitting explanation for evolution, aligning better with molecular biology.
- Critiques of the idea that everything in evolution is adaptive include the presence of spandrels and the argument that not all aspects need to be gradual.
- Sociopolitical implications are deeply intertwined with evolutionary theories, with contrasting views on naturalistic grounding and societal structures leading to significant debates and critiques.
