A fascinating addition to the literature on the nature versus nurture debate. Kevin Mitchell’s work argues that genes, the predominant factor in psychological traits, do not merely end at birth. They hugely impact the probabilistic roll of the dice as we develop (the “epigenetic landscape”). Unlike the Mendelian view, where one dominant gene leads to a clear outcome, combinations of genes are blended to make us who we are.
At the heart of all this is DNA, the simple, inert coding that has been passed on for millions of years. Mitchell has this analogy that shows its amazing ability:
The famously lengthy novel War and Peace has approximately 587,000 words. With an average of five to six letters
per word, this amounts to about three million letters. Imagine if you had to copy War and Peace, by hand, letter by
letter, but multiply the length by a thousand—that is the scale of the job that a dividing cell has to do when
replicating its genome. You’d probably forgive yourself a few errors.
Perhaps even more interesting is that DNA has a proofreading repair enzymes that fix most errors that occur.
The first part of the book drills home the concepts that psychological traits are mainly effected by 1) a multiplicity of genes acting in concert and 2) variation in how brain circuits develop. Twin studies consistently show little environmental effect on psychological traits. In fact, it is most likely the case that upbringing is effected by genes and not vice versa. A child who is patient and thoughtful, may change the way in which their parents treat them. Even “peak alpha frequency” or the way our brain processes time seems to be “at least 50% heritable.”
The second part of the book then goes deep into these concepts. For instance, synesthesia is a condition that melds colors with music tones. It is interesting to hear that musicians such as Billy Joel, Kayne West, Duke Ellington and Pharrell Williams have all had it. Other deep dives:
Intelligence:
-Flynn effect shows environmental factors at play even though there is high heritability within families.
-Adoptive siblings have IQ correlation scores of .25. Biological siblings have a score of .60.
-IQ scores taken at age 11 are good predictors of scores at age 87.
-Gene variants predict 3% of educational attainment but that could be as high as 30% as we learn more.
-High IQ individuals expend less brain activity on difficult tasks since they don’t need to think as hard.
-Facial symmetry, a marker of developmental robustness and attractiveness, also correlates to high IQ.
-People with very high IQs tend to have relatives with very high IQs.
-General intelligence accounts for 40-50% of variation in performance of IQ tests.
-Parents and siblings of people with Down syndrome typically have normal IQs because DS is caused by a single, discrete mutation.
-Males show greater IQ variance than females: there tend to be a few more intelligent and more low IQ males than females. This may be due to testosterone’s effects on variability, the instability of the X chromosome or perhaps an environment where males are encouraged at an earlier age.
-Brain size is associated with higher IQ. Yet, males have a 10% larger brain than females but similar IQs.
Gender:
-Genders exist because you want DNA diversity so you need both an egg and sperm (at least 2 different organisms, an egg cannot impregnate its own egg).
-Since female reproductive ability declines with age, females retain more juvenile features like a high pitched voice.
-If one identical twin is homosexual, the other has a 30-50% probability of being homosexual too. For fraternal twins, its 10-20%.
-If you cloned a heterosexual male, they would be attracted to women 100% of the time. If you cloned a homosexual, not all clones would be attracted to the same sex.
-On the Big 5, women tend to score higher on agreeableness and neuroticism. Slightly better on conscientiousness. Men score higher on openness to new ideas. No strong link to Extraversion.
-Developed nations, which have high gender equality, show the greatest degree of difference in personality traits between sexes. Perhaps in wealthy nations, people can expend resources to advertise the resources they have.
-Androgen insensitivity syndrome, where testosterone is not detected, could lead to a fetus developing as a women yet having a masculine brain.
Autism:
-Males show higher rates of autism, ADHD and dyslexia (about a 4:1 ratio), intellectual disability and schizophrenia (about a 3:2 ratio), stuttering (7:3) and Tourette’s syndrome (9:1). Females have a higher prevalence of depression and anxiety disorders, as well as dementia, migraine, and multiple sclerosis (all about a 2:1 ratio).
-As rates of autism diagnoses have increased, there has been a matching decrease in rates of diagnosis of “mental retardation” or “intellectual disability”
-If one of a pair of identical twins has schizophrenia, the chance that the other will be similarly diagnosed is ~50%. For fraternal twins (of the same sex), this rate is only ~15%. For autism, the rate of identical twins being coaffected is over 80%, while in fraternal twins it is only ~20%.
-Environment and heritability are not factors in schizophrenia. It is most likely caused by genetic mutation.
-The number of mutations in individuals is linearly related to their fathers’ age when they were conceived. Offspring born to 40-year-old fathers have about twice as many new mutations as those born to 20-year-old fathers.
-A child with autism may start out life with less innate interest in other people’s eyes. The child may thus miss out on the social cues of shared gaze that are so important to language development and communication. This may lead to deficits in social cognition or delays in language acquisition, even though language systems were not directly affected by the causal mutation.
The author wraps up by talking about two hot button issues today: 1) Neuroplasticity 2) Epigenetics. Neuroplasticity is the idea that the structure of the brain is not fixed. Your brain is constantly being rewired. Epigenetics is the idea that genes can express themselves differently depending on environmental cues. In both cases, Mitchell suggests that while both mechanism allow us to defy genetics in a minute way, we should all be happy with who we are.
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Reviews with images
Ignoring light-activated microRNA biogenesis
He frames his claims in the context of random mutations and evolved biodiversity despite the facts that serious scientists have detailed. For example, ages 10+ can learn how the creation of subatomic particles must be linked from cytosis to biophysically constrained viral latency and sympatric speciation.The physiology of reproduction is linked to heredity in species from soil bacteria to humans via EDAR V370A (an amino acid substitution) in mice; in populations found in North and East Asia; and in populations in the New World.I could go on about the facts about cell type differentiation for hours or refer you to MicroRNA.pro or one of my other domains. Alternatively, you could see the work that was published today: "MicroRNAs buffer genetic variation at specific temperatures during embryonic development" for comparison to our 1996 review of molecular epigenetics: "From Fertilization to Adult Sexual Behavior"
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Reviewed in the United States on January 10, 2020
Reviewed in the United States on April 23, 2022
Great book, very eye-opening and debunks many misconceptions about this idea of "nature vs nurture".
Reviewed in the United States on August 29, 2021Reviewed in the United States on September 27, 2023
Reviewed in the United States on April 3, 2019
Top reviews from other countries
Nos-tromo
Excellent review of the genetics of psychological and behavioral traits
Reviewed in Germany on March 18, 2021
Avid Reader
You can't bake the same cake twice
Reviewed in the United Kingdom on June 27, 2019jeffrey n morello
The science of how the genetics shapes the development of our brains, and our minds
Reviewed in Australia on April 19, 2020