On pages 179-180, Dr. Moalem discusses that in the time after 9/11, there was a higher number of later term miscarriages, and most involved women who had male fetuses. In speculation, he stated that this may occur as an evolutionary response: with a lower percentage of males, and more females, it may be easier to repopulate an area after a disaster. The mother may sense something stressful in the environment, and terminate the baby as a result. This pattern has been seen after other natural disasters, like the Hanshin earthquake of 1995 in Kobe, Japan.
Genetically, how are males and females different? Related to Big Idea 3, how could this miscarriage response be carried out by the body? How could the mother cause a miscarriage in a male fetus, and yet leave a female fetus unharmed? Is this truly a selective advantage? Does a large population of females and a lower population of males help cultivate a better environment for future generations? Why?
(Zachary Rane, zrane3@students.d125.org)
Genetically, females and males differ only in their sex chromosomes. Females have two X chromosomes, one from each parent, while males have an X chromosome, given by the mother, and one Y chromosome, given by the father. However, according to Dr. Moalem on page 179, when a mother experiences a large amount of stress, male fetuses are in greater danger. Stress essentially causes the production of cortisol in the mother. According to psychobiologist Miguel Diego, cortisol is able to pass through the placenta into the fetus, which could be very dangerous to the fetus. Also, cortisol can negatively affect a mother’s vascular function, which ends up reducing blood flow to the fetus. With diminished blood flow, less oxygen and nutrients can be delivered to the fetus. The reaction the mother has to stress relates to Big Idea 4, since the interactions the mother has with her environment ultimately affects her body and the child she carries.
ReplyDeleteAlso, according to the American Journal of Human Biology in October 2009, boys grow faster in the womb than girls, which means the require more nutrients to grow. Dr. Moalem also supports this claim on page 179, in which he states “males are both more demanding physiologically on the mother’s body during pregnancy and less likely to survive if malnourished as children”. If cortisol diminishes blood flow in the mother, the fetus has a large chance of being undernourished. What happens if a fetus is undernourished is that a baby may try to expand the surface of the placenta, which is the part of the fetus that attaches to the womb and transfers food from mother to child. The fact that cortisol can also pass into the baby through the placenta means that an enlarged placenta will cause even further damage to a developing fetus.
Although a large population of females and a relatively lower population of males may result in faster repopulation, the offspring of these populations are actually selected against compared to offspring of a more gender balanced population. This is due to the fact that a child is made from a combination of genes from both the mother and the father. Children from a population with more females than males will be more likely to have the same father than children from a population with an equal gender ratio. This means that the unbalanced population children will be less genetically diverse. This means that if one male in the unbalanced population and one male in the balanced has a certain disease, more children in the unbalanced population will have that disease.
Sites used:
http://www.nutritioninthewomb.org/
http://www.thebarkertheory.org/articles.php
http://www.washingtonpost.com/wp-dyn/content/article/2006/09/25/AR2006092500962.html
(Aaron Chai, achai4@students.d125.org)