Scientists have confirmed that throughout history women have outnumbered men and, consequently, contributed more to human genetic diversity.
The authors of a new study claim to have used higher resolution gene sequencing than previous research to compare the DNA of hundreds of people in modern populations around the world. Peering into their father-inherited Y chromosomes and mother-inherited mitochondrial DNA, scientists can deduce a wealth of information about historical populations. Not only did they confirm the dominance of women, but they also estimated the original population of Mesopotamia and the approximate dates of major human migrations.
"Our new sequencing technique removes previous biases, giving us a richer source of information about our genetic history," said Dr. Mark Stoneking, an evolutionary geneticist at the Max Planck Institute, in a statement. The paper he co-authored appears in the journal Investigative Genetics on Tuesday. "It allows us to take a closer look at the regional differences in populations, providing insights into the impact of sex-biased processes on human genetic variation."
Today, women do not outnumber men. According to the U.S. Census Bureau, there are about 50 million more males out of the 7.2 billion of us. And in some countries of the world, the disparity is strikingly skewed toward men. In both Qatar and in the United Arab Emirates, for example, more than 70 percent of the population is male, according to The World Bank.
Historically, however, women have enjoyed larger numbers, if not equal treatment. "The main drivers of this trend are likely to be processes such as polygyny, where one male mates with many females, and the fact that in most societies, women tend to move to live with their husbands," the researchers said in a news release. "This has resulted in females making a greater genetic contribution to the global population than males."
When the first migrants left Africa 75,000 years ago for the Cradle of Civilization — modern Iraq and Kuwait — Stoneking and his team estimate there were fewer than 100 people. They suggest there were just 15 men and 26 women. They also point to a Bering Strait crossing, from Asia to North America, around 15,000 years ago, as is commonly accepted.
Source: M. Stoneking, et al. Human paternal and maternal demographic histories: insights from high-resolution Y chromosome and mtDNA sequences. Investigative Genetics. 2014.