Posts Tagged ‘heritability’

At the end of a year, people like to make lists of top movies, books, etc.  What I plan to do instead is write about the things I learned each year. So, here are some brief highlights of things I learned in 2011:

  • Epigenetics, toolkit genes, genetic switches and how most conversations about heritability are flawed.  I learned a lot about imprinted genes from Charlene Lewis (especially BDNF), about toolkit genes from reading Sean Carroll’s Endless Forms Most Beautiful (which I highly recommend) and about all of these topics from (some of) Robert Sapolsky’s lectures on human behavioral biology (which are fantastic, and free on youtube and itunes).
  • Social belonging sits atop the hierarchy of needs.  Sister Y introduced this idea with her blog here: “the need for social belonging is more pressing than the need for food.”  I have noticed that people are far more likely to want to kill (themselves or someone else) when they have been socially shamed, rejected, or ostracized.  NYU Psychology Professor James Gilligan noted:”The emotional cause that I have found just universal among people who commit serious violence, lethal violence is the phenomenon of feeling overwhelmed by feelings of shame and humiliation. I’ve worked with the most violent people our society produces who tend to wind up in our prisons. I’ve been astonished by how almost always I get the same answer when I ask the question—why did you assault or even kill that person? And the answer I would get back in one set of words or another but almost always meaning exactly the same thing would be, ‘Because he disrespected me,’ or ‘He disrespected my mother,’ or my wife, my girlfriend, whatever.”

    In the same program, Pieter Spierenburg pointed out that murder in defense of your reputation used to be viewed as a pretty minor offense: “Originally around 1300 the regular punishment for an honourable killing would be a fine or perhaps a banishment, whereas punishment for a treacherous murder would be execution.”

  • Evidence in favor of our promiscuous past, the most interesting of which is sperm competition.  I was introduced to this topic in Sex at Dawn.
  • Life cycles of parasites.  I learned about this from Robert Sapolsky and This Week in Parasitism.  I particularly love Toxoplasma and fish tapeworm.
  • Lead and crime.  There are a lot of theories about why crime has declined since the 1990s.  These theories include:  legalization of abortion, tougher sentencing, end of crack epidemic, etc.  But I think the most interesting one is the reduction in lead exposure.  Total lead exposure was a non-decreasing function  from 1900 to 1970.  Lead exposure from gasoline increased sharply from 1930 to 1970.   We know that lead exposure, especially chronic exposure, has neurotoxic effects.  It can be particularly damaging to the frontal lobe.  Thus, we would expect that kids who were exposed to lead would be more likely to engage in impulse crimes when they are young adults.   Jessica Reyes documented the link between lead exposure and crime in the US in this paper.   The graph below, taken from her paper, overlays the lead exposure curve and crime rate curve (with a 22 year lag for lead exposure, because 22 is the average age at which violent crimes are committed, so we would expect childhood exposure to lead to have the largest impact approximately 20 years later):

    I think this is pretty compelling, and a fascinating story.  The League of Nations banned lead pain in 1922, but the US failed to adopt the measure.  The US didn’t take serious action until the 1970s.  To this day, lead paint exposure is a serious problem for people living in old homes in large cities.  I would love to see the lead exposure / crime link investigated using data from other countries.
  • Religion. I learned about the history of god, its relation to changes in civilization (how transitions from polytheism to monotheism paralleled changes from foraging to farming, egalitarianism to hierarchy), lots of cool, related neuroscience, etc.  This is work in progress.  Hopefully I will have more to say about it next year.
  • I found Sister Y’s views on nature very insightful.

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“Heritability is the proportion of phenotypic variation in a population that is due to genetic variation between individuals.” -wikipedia

Not all genetic variation is inherited.  We used to think that essentially genotype=phenotype (i.e., having a gene meant you had whatever trait goes along with it).  But now we know that all kinds of more complicated stuff is going on that determines whether genes are activated.  So, there isn’t the direct correspondence between genes and proteins like we previously thought.

Further, heritability is typically estimated from twin studies, by comparing DZ and MZ twins.   However, MZ twins likely have a more similar environment than do DZ twins.  MZ twins often share a placenta.  In addition, I have observed that they are often treated differently than DZ twins.  For example, I suspect it’s more common to dress MZ twins alike, to assume they like the same things, etc.  MZ twins also look more alike, and there is no doubt that appearance affects how people are treated.  If it’s true that MZ twins are treated more similarly than DZ twins, we might expect estimates of heritability to increase with age, which is exactly what we find in practice.

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