Evolution

02
Aug

Tracking Down Our Genetic “Adam and Eve”

Introducing Y-chromosomal Adam and mitochondrial Eve.

Two studies published this week suggest that they might have existed at about the same time, evolutionarily speaking. Here’s Akshat Rathi, writing for ArsTechnica:

Two pieces of DNA are responsible for starting these debates. One is the Y chromosome, which is present in the nucleus of human cells and is passed down from father to son. The other, much smaller piece of DNA, is found not in the nucleus of the cell but in its mitochondria, small compartments in the cell that provide its power. Mitochondria are passed down from a mother to her children.

These pieces of DNA do not undergo any mixing like the regular chromosomes. This makes tracking mutations that affect them much easier, which can help reveal their ancestry.

adam-and-eve
Two scientists argue that our genetic 'Adam'—the ancestor of all Y chromosomes—might have walked the Earth with our genetic 'Eve.'

Analyzing a person’s maternal and paternal ancestry through this method is a fruitful means of determining when a sequence originated. In 1987, Alan Wilson of UC Berkeley and his team used this “molecular clock analysis” on the mitochondrial DNA of about 147 people from around the world. They concluded that all humans descend from one woman who might have lived in Africa about 200,000 years ago—but the details holding the argument together were tenuous, and scientists remained skeptical. Now, though, Carlos Bustamante of Stanford University and Paolo Francalacci of University of Sassari have proposed a new theory.

Bustamante used 69 males from seven globally diverse populations. His team’s estimate for the existence of humanity’s common paternal ancestor is between 120,000 and 156,000 years ago. Francalacci collected DNA samples from 1204 Sardinian men. His team’s estimate worked out to be between 180,000 and 200,000 years ago. These new estimates put Y-chromosomal Adam’s age at about the same as mitochondrial Eve’s age, bringing up the possibility that they may both have walked the Earth at about the same time, give or take a few thousand years, which is much closer than previous estimates.

Read Rathi’s article to learn about implications of this research, and watch this episode from “Becoming Human,” a NOVA miniseries about how our hominid relatives transformed into early humans.