I went to a great talk at ASU’s Evolution & Medicine center, where Dr. Stearns from Yale University discussed tradeoffs 🙌🎓. I’d love to invest the rest of this day into summarizing what i’ve learned but i’ve got a dissertation to write, jobs to apply to, etc. etc… So a really short science communication bit is all i can manage!
Short version: Look at this chart.. It shows how mental illness is a result of a conflict between paternal and maternal genes. Notice how autism and szchisophrenia manifest most at the extremes of a newborn’s birth weight.
Long version: “Imprinted brain theory” argues that maternal & paternal set of genes might have antagonistic reproductive interests: father “turns off” genes that down-regulate fetal growth, resulting in enhanced growth. Mother turns on these genes, inhibiting growth.. Both actions result in normal range of weight of the newborn.
The mother is 50% related to each of her offspring.
The logic behind conflicting interests from the parents is such: since a father is uncertain that a woman’s other and future children will be his, it may be in the father’s reproductive interest for his child to use mother’s resources MORE, while the mother’s interest (considering she’ll be 50% related to all her current and future children equally) is to limit this and have resources for future kids. With polygamous mating, offspring’s genes from the father will be selected to extract MORE from the mother, and maternal genes will be selected to resist such increased extraction of bodily resources.
To simplify: father needs current baby to use up as much of mother’s resources to grow bigger/stronger/have higher chance of future reproductive success because he can’t be sure her other kids will actually be his.
A conflict arises when action of one parent is cancelled by disrupting imprinting- so disruption of maternal interests would result in an uninhibited expression of paternal interests. Such disruptions result in abnormally low or high birth weight (along with other factors such as behavioral aspects- the extremes of which are considered mental illnesses). Extreme genomic imprinting in favor of MATERAL genes will result in lower birth weight, and is argued to cause psychosis (schizophrenia spectrum) while the opposite causing autism spectrum disorders. The chart above shows how such abnormalities in weight are indeed associated with autism & schizophrenia.
Mariya V. PhD 