A Closer Look into the Story of Mitochondrial Eve
The molecular clock, formulated in 1967, counts changes in genetic material. It can help construct phylogenies of species; however, it is not applicable to human modern human populations because the exchange of genes has been happening since the very beginning. However, the molecular clock can be used with mitochondrial DNA, which is inherited from the mother. We can trace all the DNA back to one person, using a model described in the book. The human population is finite, and some women will have no children, and the others will only have sons. There is always a chance that at the next generation, a woman’s mitochondrial DNA lineage will end. Over time, there will only be one lineage left.
Rebecca Cann, the researcher working on investigating mitochondrial Eve, first collected DNA from placentas from women that had given birth to estimate the rate of change of the mitochondrial DNA. Using the archaeological record to calibrate her clock, Cann was able to estimate the date that mitochondrial Eve was alive to around 290,000 to 140,000 years ago. Because the mitochondrial DNA samples used had some problems in the sample diversity, another group repeated the study. Based on their results, the date was moved back to 249,000 to 166,000 years ago.
In the book, the study is glossed over but in the article, the author goes over the detail of finding mitochondrial Eve. The author says that the results of the study are consistent with a genetic “sweep”, where a strong selective pressure favors a single variant of mitochondria to survive. The story of mitochondrial Eve involves both an epidemic – like transmission of the trait, as well as it possibly being a evolutionarily stable strategy. The mitochondrial Eve mitochondria in descendants could have possibly produced more energy so that daughters that carried it had an advantage over others. Therefore when placed into a population of other mitochondrial DNA, carriers of the mitochondrial Eve DNA would eventually crowd out the other kinds of DNA. As more and more of this DNA was passed on through the generations, there is an even greater chance for further generations to carry mitochondrial DNA from mitochondria Eve.