Human Behavioral Biology Lectures by Robert Sapolsky Summary (Part 1)

Key Takeaways:

• People who are treated more positively during childhood development are more extroverted in adulthood.
• People who are taller are treated better and considered more attractive.
• Political affiliation is 70% heritable.
• Aggressiveness comes from higher pain sensitivity.
• “Environment” does not begin at birth. It begins at conception. The fetus is altered based on hormones, calories, external voices and sounds, etc. These can cause life-changing effects before the fetus is born.
• Bad genes (predisposition towards anxiety, antisocial behavior, or aggressiveness) only get “activated” if you have bad childhood experiences.
• Studies of twins separated at birth give us huge behavioral insights. They found that there is 50% heritability in IQ, trait extraversion, and aggressiveness.
• The age that a child reaches puberty is determined by the age of the mother (her estrogen levels) when she gave birth.
• Heritability is not what you think. Heritability is the rate of variability, not the average prevalence.
• For marketers: If you want someone to remember your product, make the advertisement scary. People remember emotional (fear) events.
• Smiling repeatedly over the course of an hour will make you feel happier.
• Memorize the key biology, physiology, and neuroscience terminology. It will make your life far richer.

Lecture 2: Behavioral Evolution

• Evolution was a known theory before Darwin. Darwin came up with a mechanism for evolution—natural selection.
• Darwinian principles:
• There are traits that are heritable (not genetic, heritable).
• There is variability among traits.
• Some versions of those traits are more adaptive (more fit in a Darwinian context) than others.
• Sometimes there is a mutation—a new trait.
• The Darwinian principles above apply to physical traits as well as behaviors (personality traits).
• Animals do not behave for the good of the species.
• Animals behave to pass on their genes.
• 3 Types of Selection
• Individual selection—the selfish gene. Animals want to reproduce as much as possible to that there are a many copies of their genes as possible.
• Sexual selection. Selecting for traits that have no value in terms of survival but for some reason the opposite sex is attracted to it. Those traits will become more common.
• Natural selection. Traits that cause an individual to survive make them more likely to survive and reproduce.
• Your life from a genetic viewpoint is worth 1 identical twin, 2 siblings, or 8 cousins. Because your siblings have 50% of your genetics.
• Reciprocal altruism is found throughout biology. Even at the bacteria level. Animals reciprocate good deeds.
• Humans are more attuned to noticing cheating than kindness.
• When do you cooperate and when do you cheat?
• Game theory answers that question. There are games that have mathematically optimal strategies.
• The prisoner’s dilemma is an essential example in game theory.
• Tit for tat is the best strategy in a prisoner’s dilemma. This solution came from computer simulations. You start off cooperating but if they cheat, you cheat the next round, if they cooperate, you cooperate the next round.
• Why does tit for tat work so well?
• It starts off nice—cooperation
• It retaliates if you do something bad
• It is forgiving—if you go back to cooperating, it will too
• It’s clear cut—not probabilistic
• Tit for tat strategies are vulnerable to signal error. If someone is cooperating but the other person thinks they cheated (due to a communication error) they will continue to go back and forth cheating each other.
• “Forgiving tit for tat” solves the above problem. Every X rounds, you do cooperation to get back on the cooperating track.
• Is it a beneficial strategy to make your opponent think you’re crazy and will do anything? Maybe at times.
• Animals in the wild naturally use the same tit for tat strategy.
• Naked mole rats are one of the weirdest animals. They have insect-like colonies.
• Species with high sexual dimorphism where one sex is larger will result in the larger sex being more aggressive and there will be a larger disparity between reproductive success within the larger sex. Females select for the largest male because it makes her offspring big and healthy. Tournament species.
• Species with low sexual dimorphism where both sexes are roughly the same size will result in relatively equal levels of aggression and reproductive success. Females select for parental ability—can they provide for the kids? Lots of male parental behavior. Females cheat on these males because (1) the males will raise the kids and (2) their genes aren’t noteworthy. Pair-bonding species.
• ~1% of pregnancies are twins.
• Economic and demographic polygamy.
• Economic: the wealthiest make gets all the women
• Demographic: the warriors get multiple women after the war because most of the men die in war, so there are fewer men for every woman.
• Most cultures allow polygamy but most males in those cultures are not polygamous because only the best males can be polygamous.

Lecture 3: Behavioral Evolution II

• Males try to trick females into thinking their genes are better so the females will mate with them.
• There are animals of every species that kill infants. It tends to be adult males killing the offspring of other males.
• Older females and grandmothers defend their children the most because they have low or no reproductive capabilities.
• Pseudo-ovulating is when a female gives out signs of ovulation even though she is pregnant. This tricks males who may want to kill her infant into thinking the child is theirs, so they don’t kill the kid.
• Having sons is high-risk, high-reward. It’s more likely that they do not reproduce but there is a chance that they become hyper-successful and have many kids. Girls are less risky. They are virtually guaranteed to have kids but they can only have ~5 max.
• Boys require more resources to bring to term. In times of famine, more girls are born.
• Sometimes there are 2 males at the top. What keeps them from killing each other’s offspring? They’re usually brothers.
• Levels of cooperation will be higher in smaller groups because of a higher degree of relatedness.
• Cooperation in a hostile group causes you to lose. But cooperation in a cooperative group causes everyone in the group to win.
• At different times, the most important aspect of natural selection could be a single gene, a single organism, or a single group.
• “Eventually, all of the social sciences will be under the wing of evolutionary biology.” - (a bold statement from) E. O. Wilson
• Assumptions of evolutionary biology:

1. Heritability. Physiology and behaviors are heritable. (Counter argument: show me the genes that make it heritable.)
2. Adaptiveness. There was a selective reason for why certain traits emerge and succeed. (Counter argument: these are just stories that rationalize behaviors. Whoever has the best story gets tenure. Show me experimental evidence that it’s adaptive. Some behaviors can be inadvertent byproducts of something else—rather than being adaptive.)
3. Gradualism. It’s incremental. Evolution and change take time.

Lecture 4: Molecular Genetics I

• Everything flows from DNA. (This is wrong actually—see below.)
• 95% of DNA are on/off switches for the 5% of DNA that have physiological or behavioral effects. The 95% are called transcription factors.
• DNA are essentially lines of code. The transcription factors determine which “lines of code” run. So what influences transcription factors? The environment.
• Epigenetics—when the environment or your behaviors affect the way your genes work.

Lecture 5: Molecular Genetics II

• There’s a gene that can be turned on that predicts divorce. Do we have free will? Probably not.
• Women’s immune system shoots up after child birth which can cause or worsen autoimmune disorders. Women’s immune system weakens during pregnancy so as to not reject the baby.
• Diabetes is driven by caloric excesses in westernized diets.

Lecture 6: Behavioral Genetics I

• Studies of twins separated at birth give us huge behavioral insights. They found that there is 50% heritability in IQ, trait extraversion, and aggressiveness.
• The age that a child reaches puberty is determined by the age of the mother (her estrogen levels) when she gave brith.
• “Environment” does not begin at birth. It begins at conception. The fetus is altered based on hormones, calories, external voices and sounds, etc. These can cause life-changing effects before the fetus is born.
• Eggs have mitochondria and sperm don’t. 100% of the mitochondrial DNA of a child is from the mother.
• People who are taller are treated better and considered more attractive.
• People who are treated more positively during childhood development are more extraverted in adulthood.
• Political affiliation is 70% heritable.
• Aggressiveness comes from higher pain sensitivity.

Lecture 7: Behavioral Genetics II

• Antisocial feral aggressive dogs tend to look like wolves over time.
• Biologists used to find two people with the same genes except for one gene that caused a health problem. This allowed them to narrow down on which gene it was. They were somewhat accurate.
• Today, we have gene sequencing, which allows biologists to find specific genes.
• Most issues (diabetes, psychological problems, etc.) stem from more than one gene.
• When cells split, they’re not perfect clones. There are transcription factors and mitochondria that are more on one side than another.
• Around (55:00) Sapolsky explains heritability. It’s not what you think. Heritability is the rate of variability, not the average prevalence.
• You cannot ask: what does this gene do? You have to ask: what does this gene do in a particular environment?
• Bad genes (predisposition towards anxiety, antisocial behavior, or aggressiveness) only get “activated” if you have bad childhood experiences.
• Breastfeeding maximizes IQ?

Lecture 8: Recognizing Relatives

• Inherited is not the same as heritability.
• Larger families on average have lower socioeconomic status.
• When doing a study, you have to ask yourself: (1) is the effect reliable? And (2) is the effect important (big)?
• Animals use olfactory senses to determine if another is a relative.
• Autoimmune diseases occur when the immune system believes that a friendly is an enemy.

Lecture 9: Ethology

• Psychology used to be philosophical. The young turks of psychology wanted to make it a science.
• History of ethology:

1. The blank state—human behavior is completely determined by the environment.
2. Reinforcement theory—human behavior can be completely determined by the rewards and punishments given in response to a behavior.
3. B. F. Skinner—he wrote Walden Two and said that utopia could be brought about with the “correct” application of reinforcement theory.

• Wild rats have a thicker cortex (a good thing) than lab rats even given the best environmental conditions.
• Rats laugh. Peterson talks about this study too. Affective neuroscience.
• When people smell the sweat of someone who is fearful, the person who smells the sweat rates pictures of faces as more fearful.
• (All) species have cute baby faces. Other species recognize a cute baby face of another species (a polar beat will recognize a baby monkey’s face as cute, for instance).

4. The Disney animators studied what made baby animal faces cute and put those features into their animations.

• Animals have to learn certain behaviors (they’re not all innate). A monkey has to learn, for instance, how to eat a scorpion without getting stung.
• Say event B caused event A. We often (incorrectly) believe the event that happened closest to A caused A. If you ate food that gave you a stomach ache later that day, for instance, you might attribute the stomach pain to the opera that you went to see because it was the event closest to the onset of the stomach pain.
• On the question of animal awareness by Donald Griffin

5. People have been studying animal awareness ever since but it was laughable at the time. Griffin only published the book when he was old and had tenure.

• Studies show that chimps have theory of mind. They know that other chimps do not necessarily have the same information they do. For chimps, this only applies to competition, not cooperation.
• Birds have theory of mind.

Lecture 10: Introduction to Neuroscience

• The hippocampus is responsible for forming new memories.
• The amygdala is important for fear and anxiety responses.
• The hypothalamus and pituitary gland control hormones. Hypothalamus controls: Fight, flight, feeding, and reproductive behavior.
• Santiago Ramon y Cajal (1852-1934) is the grandfather of modern neuroscience.
• Dopamine is a neurotransmitter.
• Epinephrine (adrenaline) is a neurotransmitter. (Fight or fight)
• Serotonin is a neurotransmitter.(sleep, appetite, mood)
• Psilocybin, LSD, and mescaline interact with serotonin receptors because they have a similar structure to serotonin.
• You have to be extremely careful in pharmacology because a drug can have unexpected side effects.

Lecture 11: Introduction to Neuroscience II

• Glutamate is a very important neurotransmitter. It’s excitatory.
• There are more than 40 neurotransmitters in the human nervous system.

• Stress responses can enhance memory in the short term. Because evolutionarily, you want to be able to remember and analyze events that cause fear (so that you can prevent them in the future). But stress over the long term has negative effects.
• Emotional memories last longer.
• Alcohol makes it more difficult to remember.
• Some people can’t remember anything (hippocampus damage/removal) and some people have a photographic memory. But most people fall somewhere in between.
• Signal is good information. Noise is bad information.
• Neurons can send their message multiple times and/or block the messages of neighboring neurons to try to increase the signal to noise ratio.
• There are 2 kinds of pain. Sharp fast pain and a dull lasting pain. There are 2 different kinds of neurons that carry the types of pain.
• The fast pain can start the slow (dull) pain by talking to the neurons around it. The slow pain gets the fast pain to stop by talking to the neurons around it. Generally, sharp pain happens first and is replaced by slow pain. It makes you pay more attention to the pain in the moment so that you can get away from what caused the pain but then reduces the pain because it’s likely that you know you’re hurt.
• For marketers: If you want someone to remember your product, make the advertisement scary. People remember emotional (fear) events.
• Autonomic nervous system—behaviors that happen automatically. Heart beating, digesting, goosebumps, orgasm.
• The central nervous system (CNS) is the brain and spinal cord.
• The peripheral nervous system (PNS) is everything else.
• The PNS contains the somatic (voluntary) and autonomic nervous systems.
• Sympathetic nervous system = high blood pressure, high pulse, stress, etc.
• Parasympathetic nervous system = relaxed, calm, rest, repair.
• Males can’t get an erection when the sympathetic system is engaged.
• The sympathetic system gets engaged in orgasm.
• 60% of erectile dysfunction is due to stress and not a physiological problem.
• The receptors on organs can be opposite. The GI tract, for instance, has the opposite ACh and NE receptors than the heart. Because when the parasympathetic system is on, we want to excite the GI tract (so we digest food) but inhibit the heart (so that our heart doesn’t beat too fast).
• Beta blockers block the excitatory NE receptors on the heart so that the heart rate slows down and you are more relaxed/less stressed.
• The hypothalamus is the center of regulation for the ANS.
• The parasympathetic and sympathetic nervous systems regulate blood pressure. If you get into an accident and lose blood, for instance, your sympathetic nervous system would increase your blood pressure to make up for the blood loss. If your blood pressure gets too high, your parasympathetic nervous system lowers your blood pressure.
• The limbic system controls emotions, behavior, and memory.
• Seeing someone you hate can cause a similar response to losing a lot of blood.
• Many of the symptoms of depression (loss of pleasure, pain pathways on, loss of appetite, loss of libido, exhaustion) are the same as if your sympathetic nervous system was overly activated. The cortex can activate those systems by having bad thoughts.
• Plasticity of the ANS. The ANS can change over time. Sensitization: you can get more scared of things by not facing them. Desensitization: you can get less scared of things by incrementally facing them. Your automatic blood pressure responses to sensory stimuli will change based on if you face or run away from your fears.

Lecture 12: Endocrinology

• Neurons have to use neurotransmitters to communicate with each other.
• Endocrine signals are about hormones (chemical messengers) in the blood.
• Neurotransmitters are only between neurons. Hormones are in the blood (throughout the body).
• Dopamine, epinephrine, etc are neurotransmitters but they are hormones when in the blood.
• Peptide hormones: quick onset, short duration, main effect: protein activity.
• Steroid hormones: slow onset, long duration, main effect: transcription.
• The endocrine glands (below) secrete hormones.
• The brain has control over the other endocrine glands.
• The pituitary gland
• Anterior pituitary hormones: FSH, LH, ACTH, TSH, prolactin, endorphins, GH
• Posterior pituitary hormones: vasopressin and oxytocin
• Hormone to Neuron: An Epic Journey
• Can it get past the blood-brain barrier?
• Does the neuron have the right receptor?
• Once it binds, how can it influence activity?
• The blood-brain barrier regulates what things can get in and out of the brain.
• More hormone receptors typically means you are more sensitive to hormones.

Lecture 13: Advanced Neurology and Endocrinology

• Jerome Lettvin was a great neuroscientist.
• The amount of messengers is important but the amount of sensitivity to messengers is just as important. Ex) if the body down regulates sensitivity to insulin, the pancreas will produce more and more insulin. The body will see that there’s too much insulin and down regulate further. The pancreas will continue to produce more and more insulin until it works so hard that it can’t produce insulin anymore. This causes diabetes. (42:22)
• There are receptors at the end of neurons. Other neurotransmitters can connect to them and cancel signals from the neuron. This is neuro-modulatory rather than neurotransmitter.

Lecture 14: Limbic System

• The limbic system is linked to emotion.
• Memorize the key biology, physiology, and neuroscience terminology. It will make your life far richer.
• The frontal cortex is the most interesting part of the brain according to Sapolsky.
• Studies suggest that the frontal cortex developed for social interactions and communication.
• The frontal cortex doesn’t fully develop until the mid 20s in humans. It is larger in humans than in other animals. It is used for impulse control and other things.
• People with PTSD have a larger amygdala.
• People with long-term major depression have a smaller hippocampus—it atrophies.
• Amygdala: fear, anxiety, aggression
• Hippocampus: learning/memory, turning off the stress response. It makes sense that this area of the brain is intertwined with both memory and stress because you want to remember stressful events so that you can prevent them in the future. And it allows you to remember how you got out of a stressful situation last time.
• Smiling repeatedly over the course of an hour will make you feel happier.

Lecture 15: Human Sexual Behavior I

• Attractivity: how attractive an individual is.
• Receptivity: how receptive an individual is.
• Proceptivity: the active behaviors that are acted out in response to being attracted to.
• The attractivity of an individual causes another to have proceptive behaviors towards that individual which will be accepted or rejected based on how receptive they are.
• Why do females have orgasms? They’re not necessary for conception or pregnancy.
• Other monkeys and apes also have female orgasms.