London, May 13 (ANI): A large scale, quantitative test has proved Darwin's theory of universal common ancestry (UCA), linking all forms of life by a shared genetic heritage from single-celled microorganisms to humans, as correct.
In his 1859 book, On the Origin of Species, the British naturalist proposed that, "all the organic beings which have ever lived on this earth have descended from some one primordial form."
Over the last century and a half, qualitative evidence for this theory has steadily grown, in the numerous, surprising transitional forms found in the fossil record, for example, and in the identification of sweeping fundamental biological similarities at the molecular level.
Still, rumblings among some evolutionary biologists have recently emerged questioning whether the evolutionary relationships among living organisms are best described by a single "family tree" or rather by multiple, interconnected trees-a "web of life."
Recent molecular evidence indicates that primordial life may have undergone rampant horizontal gene transfer, which occurs frequently today when single-celled organisms swap genes using mechanisms other than usual organismal reproduction. In that case, some scientists argue, early evolutionary relationships were web-like, making it possible that life sprang up independently from many ancestors.
Biochemist Douglas Theobald said: "Let's say life originated independently multiple times, which UCA allows is possible.
"If so, the theory holds that a bottleneck occurred in evolution, with descendants of only one of the independent origins surviving until the present. Alternatively, separate populations could have merged, by exchanging enough genes over time to become a single species that eventually was ancestral to us all. Either way, all of life would still be genetically related."
Harnessing powerful computational tools and applying Bayesian statistics, Theobald found that the evidence overwhelmingly supports UCA, regardless of horizontal gene transfer or multiple origins of life. Theobald said UCA is millions of times more probable than any theory of multiple independent ancestries.
Theobald added: "There have been major advances in biology over the last decade, with our ability to test Darwin's theory in a way never before possible. The number of genetic sequences of individual organisms doubles every three years, and our computational power is much stronger now than it was even a few years ago."
Theobald is the first to formally test Darwin's theory across all three domains of life. The three domains include diverse life forms such as the Eukarya (organisms, including humans, yeast, and plants, whose cells have a DNA-containing nucleus) as well as Bacteria and Archaea (two distinct groups of unicellular microorganisms whose DNA floats around in the cell instead of in a nucleus).
The study has been published in Nature. (ANI)