Recognizing Relatives. 1h 20m Robert Sapolsky video.
The first half-hour is an effective review of the course to date. He summarizes behavioral genetics (the preceding two lectures) by these two statements: "The fact that humans usually have 5 fingers reflects the fact that this trait is inherited. The fact that when there are some circumstances of humans having other than 5 fingers, it is overwhelmingly due to environment is an indication that nevertheless the variability (heritability) is essentially 0%." Does that clear it up for you?
Then he reviews the definition of epigenetics at three levels: 1) the way environment affects biology (genetics), 2) the way environment turns genes on and off, and 3) the regulation of chromatin remodeling, methylation of genes, etc.
Sapolsky uses a review of two studies to help us understand how to be critical of the scientific literature and learn what questions to ask to put such studies into perspective. He is brilliant. The effect is masterful. One of the studies proved that first borns have a higher IQ than later borns. Among the many questions that we as critically thinking reviewers of a scientific study ought to ask are Did the study effectively control for other factors? How good is the science / statistics? And critically, how big is the effect? Is the 2.3 IQ point advantage of first borns meaningful?
Then the last 50 minutes of the video discusses the problem of how do organisms recognize kin (relatives)? There are three basic means of recognizing relatedness: 1) innate which is effectively olfactory (of the sense of smell) 2) learning or imprinting (learning that occurs at a particular phase such as right after birth), and 3) cognitively (thinking it out).
The major histocompatibility complex is a protein that provides a unique signature of "self" and is presented on the cell membrane of every cell in the body. It is essential for immune functioning. Sapolsky suggests that pheromones (chemical triggers of social behavior) may signal both uniqueness ("self") and relatedness. The "self" protein may be built from an arguably unique juggle of the genes (randomness) plus some way of capturing the pattern that is your genome which is shared more closely with closer relatives. It is probably similar (or identical) with the mechanism used for the immune function. Receptors could sense relatedness by how good a lock-and-key protein fit is made.
In the olfactory bulb, the hormones oxytocin and vasopressin are active in mediating pheromone detection by increasing the number of receptors thereby increasing sensitivity. There is an emerging literature suggesting that mutations in the genes related to oxytocin and vasopressin affect autistic families. Austism is characterized by enormous deficits in normal socialization, interaction, social bonding, and social affiliation. Anosmia is the inability to smell. A social anosmia refers to being unable to distinguish between individuals.
Adult neurogenesis (generating new nerve cells) only happens in two areas of the brain: 1) the hippocampus (associated with learning & memory) an enriching environment stimulates neurogenesis whereas stress generates less and 2) behind the olfactory bulb in females around the time of pregnancy prolactin stimulates neurogenesis to build a revamped olfactory system to be ready at birth (this could be the reason that smell and taste are weird during pregnancy: it might be a spandrel!).
Martha McClintock (the one who published on the Wellesley effect) tested swabs of armpits to determine that humans have an innate ability to distinguish degree of relatedness: she determined that our 3rd cousins have the most "appeal" (a 3rd cousin is the optimal level of relatedness to minimize genetic effects of matings with close relations but maximize kin selection).
Some species do not have this innate mechanism. Imprinting is how many organisms learn who Mom is and how Mom learns who is their kid. The learning is innate, but it takes experience to set the learning upon a specific individual. Different species use different degrees of smell, sound, and sight.
Some animals (including humans) recognize relatives cognitively (through thinking). Sapolsky reports that baboons do it based on a statistical kind of thinking. David Sloan Wilson has detected cognitive effects in sun fish: if a male sees another male with his mate, he won't take care of the kids. In humans, sheep, pigeons, and primates, the fusiform cortex (use "fusiform face area" in Wikipedia) supports facial recognition (it is inactive in autistic children). At birth mothers and their babies have olfactory recognition: babies tend to turn their heads towards Mom's smell. There is also some imprinting from hearing Mom's voice in utero and making more sucky motions indicating interest when she repeats those sounds after birth.
Anthropologist Joseph Shepher found that humans who played extensively together before the age of 6 (in a large study of Israeli kibbutzim), never married or had relations with those peers. Arthur Wolf, an anthropologist at Stanford, found that arranged marriages in Taiwan between couples who were raised together from a young age were disastrous. Wikipedia's article "Incest taboo" suggests that the effect is not supported by all studies.
Pseudo-kinship is the phenomenon in humans wherein non-relatives feel like a band of brothers (e.g., military units). Pseudospeciation is where we are manipulated to perceive some humans as hardly counting as being human at all. Are these unique traits of humans? Could we represent them in a positive, non-pathological framing or are these troubling effects?
8. Recognizing Relatives