Aug 18, 2010 08:15 GMT  ·  By
In cell biology, a mitochondrion is a membrane-enclosed organelle found in most eukaryotic cells.
   In cell biology, a mitochondrion is a membrane-enclosed organelle found in most eukaryotic cells.

Mitochondrial Eve (mtEve), the mother of all humans, lived about 200,000 years ago according to Rice statisticians' new found method, that could actually be the most complete statistical study of our species' genetic link with our maternal ancestor that was ever made.

The research was based on a comparison between 10 human genetic models, each one having specific theories on how to find out when Eve lived, depending on human migrations, on the way they expanded and spread across the planet.

Scientists tried to date mtEve by using modern genetic techniques, like comparing genetic profiles of random blood donors, and depending on differences between several genes, the degree to which the two donors are related can be established.

Because the entire human genome has more than 20,000 genes and comparing the differences among them for distant relatives is a huge task, difficult even for the most advanced computers, researchers used mitochondrial genomes to find common ancestors.

This method is somehow less complicated as mitochondria (the small organelles inside all human cells) have their own genome and each person's mitochondrial genome is inherited from the mother, so all mitochondrial lineages are maternal.

Mitochondria also have only 37 genes than seldom change and they contain a "hypervariable" region, that changes fast enough to provide a molecular clock calibrated to times comparable to the age of modern humanity.

In order to find out the age on mitochondrial Eve, researchers have to convert the measure of relatedness between random blood donors into a measure of time.

Co-author Krzysztof Cyran, vice head of the Institute of Informatics at Silesian University of Technology in Gliwice, Poland said: “You have to translate the differences between gene sequences into how they evolved in time, and how they evolved in time depends upon the model of evolution that you use.”

Each model gives its own coefficient, that can be combined into an equation that should give the answer for when mtEve lived.

Co-author Marek Kimmel, professor of statistics at Rice said that the “findings underscore the importance of taking into account the random nature of population processes like growth and extinction.

“Classical, deterministic models, including several that have previously been applied to the dating of mitochondrial Eve, do not fully account for these random processes.”

Every model has its theories, with their own mathematical implications, and some of the theories are not even applicable to human populations.

The attempt to date mtEve is also an example of how scientists investigate the genetic past so that they can find out more about mutation, selection and other genetic processes that are important in the evolution of diseases.

“This is why we are interested in patterns of genetic variability in general; they are very important for medicine,” Kimmel explained.

This research is available online in the journal Theoretical Population Biology.