Do all living things on planet Earth share a common ancestor? The scientific debate has been raging on for quite awhile. By this, I am by no means referring to the debate between the Creationist ‘special creation’ theories (where each species was individually created) and the theory of evolution and common descent. On the contrary, I am referring to a debate between evolutionary biologists – Did life arise just once through a single ancestral form (referred to as LUCA – the Last Universal Common Ancestor), which then branched out into many forms, or did life arise multiple times, which then ‘interbred’ with one another (with some becoming extinct) before branching out into all forms of life we see from past to present? We may have the answer now:
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.
Harnessing powerful computational tools and applying Bayesian statistics, Theobald found that the evidence overwhelmingly supports UCA (Universal Common Ancestor), 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.
The full article can be found here:
The original paper was published in the journal Nature, and can be found here: