All of life shares a common ancestor, new paper confirms.

darjeeling

An ambitious new bit of work published last week set out to test whether all three domains of life (bacteria, eukaryotes - yeast, plants, animals - and the mysterious archaea) did indeed share a common ancestor.

It's long been thought that all living organisms share a common ancestor. Even Darwin thought so, way back when. Since his day, we've found that that all of life uses a near identical genetic code for turning the information stored in the DNA of genes into working proteins. Also, we find in all living things a core set of 23 genes coding for the machinery to make proteins. However, we've not had a proper test of this universal common ancestry until now.

In a paper in Nature last week, Douglas Theobald took the protein sequences of the universal 23 genes from 12 species, 4 from each domain of life. He then set up different models for how the proteins could have evolved - independently, from a common ancestor, with or without horizontal gene transfer etc. - and tested how likely each model was. Single ancestry won out overwhelmingly. This says that we humans share common ancestry with bacteria and with archaea.

The paper doesn't offer insight into whether life originated only once or many times. That's not possible to test - at least for now. If there were multiple starts to life, though, they either merged together in our common ancestor, or all went extinct apart from that ancestor.

Nature links:

Paper (subscriber access only)
News & Views (subscriber access only)
Podcast

Panda's thumb has a nice (& free) write-up here.

Kevster

This just adds weight to what I've always believed myself about the different kingdoms of life and all lifeforms contained within them. However, it's not inconceivable that life could have 'sprung up' independently in different locations on the early Earth.

By the way, you've misrepresented what the authour said. Those proteins he was analysing in the study are only "proposed to be orthologous" across the different kingdoms. Someone reading just your post would think that it is widely accepted that these proteins are common to all life.

darjeeling

Kevster wrote: »

This just adds weight to what I've always believed myself about the different kingdoms of life and all lifeforms contained within them. However, it's not inconceivable that life could have 'sprung up' independently in different locations on the early Earth.

Yes, we don't know that yet, as the paper points out. If this paper has it right that every living thing we know of shares a common ancestor, then we can suppose that life only arose once, or that independently arising lifeforms merged, or all went extinct apart from our common ancestor.

Kevster wrote: »

By the way, you've misrepresented what the authour said. Those proteins he was analysing in the study are only "proposed to be orthologous" across the different kingdoms. Someone reading just your post would think that it is widely accepted that these proteins are common to all life.

I hope I didn't - when setting out the problem, I didn't say whether these genes that are found in all of life and which I referred to as 'core' and 'universal' are taken to be orthologues, or whether they arose independently in different domains of life, and converged on the same sequence. That, after all, was what the paper set out to test.

Kevster

darjeeling wrote: »

I hope I didn't - when setting out the problem, I didn't say whether these genes that are found in all of life and which I referred to as 'core' and 'universal' are taken to be orthologues, or whether they arose independently in different domains of life, and converged on the same sequence. That, after all, was what the paper set out to test.

Indeed, I think it was I who misrepresented you! I just re-read your original post twice and it makes sense to me now what you were saying. Sorry about that.

kevin