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Who Comes First, Male or Female?

People used to think that X chromosome appeared many years longer than Y chromosome did. However, American scientists have recently pointed out that the most recent common ancestors of human male came into being at almost same time with the females.

Previous studies showed that the most recent common ancestors of human female came into being much earlier than the most recent common ancestors of human male. However, Mr. G. David Poznik and his colleagues of the Stanford University have given a different explanation of the origin of the Y chromosome in their thesis in the latest edition of “Science”: the most recent common ancestors of human male did not come into being obviously later than human female.

Y chromosome of human being is genetically inherited from father to son, while the mitochondrial DNA comes from the mother, so based on the analysis of the mutation of Y chromosome and mitochondrial DNA, the researchers are able to find the trace of the most recent common ancestors of the whole human male and female — they are vividly called the “Y chromosome Adam” and ” Mitochondria Eve”. In this study, the researchers reveal that the times when “Adam” and “Eve” may come into being roughly coincide: “Adam” appeared 120,000 –156,000 years ago and “Eve” appeared 99,000 year—148,000 years ago.

By applying new high-throughput sequencing technologies, the researchers have completed the comparative study on Y chromosome of 69 males who come from the different regions in Namibia, the Democratic Republic of the Congo, Gabon, Algeria, Pakistan, Kampuchea, Siberia and Mexico etc… As a result, the researchers have obtained ten million nucleotides messages of Y chromosomes from each subject and found there are 11,000 types of sequence differences of Y chromosome among the subjects. With such information, the researchers could establish the systematic relationship and time axis of these differences more accurately than before in estimation of the mutation rate of Y chromosome. Then, the researchers have done the identical analysis of mitochondrial DNA in 69 males and 24 females. The final result shows that the times when the most recent common ancestors of male and female came into being could overlap.

Previous studies suggest that “Adam” and “Eve” appeared 50,000 -115,000 and 150,000 -240,000 years ago respectively. However, Mr. Carlos Bustamante, professor of genetics at the Stanford University and corresponding author of the thesis said that “According to the previous views, the most recent common ancestors of human male appeared much later than the most recent common ancestor of human female, but our research shows that there is no such difference between them.”

However, it is now difficult to determine what this result really means. This time relationship may be just a coincidence. Mr. G. David Poznik says that “To a large extent, this is a random process. Some lineages disappeared, while other successfully remained. However, there may exist some historical factors, which help merging of such lineages in the particular period.”

Reference: EurekAlert!
Image source: lds.org

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