Writing project (due next tuesday).
Some have suggested that the age of weaning of infants from the breast is subject to parent offspring conflict. For example, infants might want to breastfeed longer than the mother would like. Breastfeeding tends to suppress ovulation and delay pregnancy. Give an evolutionary hypothesis for why infants might exhibit behavior that promotes longer breastfeeding. What behaviors might these be? The infant has 1/2 maternal derived genes and 1/2 paternal derived genes; which of these would these be expected to prolong breastfeeding?
This is the article on aspirin and inluenza that I mentioned during today’s lecture:
The following s a wrap up of tuesday’s lecture:
Genetic conflict occurs between parents and between mothers and offspring. It is on of the most counter-intuitive ideas in evolutionary medicine.
Bottom line: babies do not always get along with their mothers, even while in the womb! Placentas do not get along with pregnant mothers either, with surprising results! This conflict arises from the fact that placentas are derived entirely from paternal genes. And of course the baby’s genes are 1/2 maternal and 1/2 paternal on average. Paternal-derived genes might benefit if more resources are delivered to the baby than the mother would like to give up. This sets the stage for a tug-of-war between genes from the mother and genes from the father.
Gestational diabetes provides a quick example: Glucose is a fuel that allows growth of the fetus. Paternal derived genes might cause increased glucose delivery to the fetus. Increased glucose causes the baby to grow slightly larger, but at some cost to the mother. The overall size of a baby might reflect a balance between paternal genes that increase the size of the fetus versus maternal genes that resist these increases. When the balance is tipped too far in favor of paternal genes, the mother may suffer from gestational diabetes.
This brings up all sorts of questions. For example:
1. Isn’t it bad for the baby too to be large, causing difficulties at birth? If the baby dies at birth it would be of no benefit to paternal derived genes to have a larger baby.
2. Shouldn’t the interests of baby and mother be in perfect alignment, since they are dependent on each other for successful reproduction?
3. Do paternally-derived “conflict” genes get expressed differently for one-night stands versus a long term committed relationship?
The answers are: yes, no, and yes.