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My Name is LUCA—The Last Universal Common Ancestor

Anthony Poole

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This article accompanies a companion article by the same author, “What is the Last Universal Common Ancestor (LUCA)?
 

Looking down a microscope at a human cell, there is not a lot that it seems to share in common with a bacterial cell. But just as linguists have been able to establish that all human languages have a common origin, so it turns out that all cellular life has a common origin. The ancestor of all life on Earth today has been dubbed LUCA, short for Last Universal Common Ancestor. The fact that there must have been a LUCA was first made clear in the 1960s when the genetic code was deciphered and found to be universal. Almost forty years since the code was cracked, the emphasis is now on trying to reconstruct LUCA, but the emerging picture is substantially complicated by new insights into the evolutionary history of life.

September 2002

Note: Because some of the information in this article may be outdated, it has been archived.

1. Introducing LUCA

LUCA is short for Last Universal Common Ancestor, and it is from this organism that every living cell on the planet has descended. LUCA does not represent the earliest stage in the evolution of life — it is widely accepted that before the evolution of proteins and DNA (which are common to all cellular life) there was a period where RNA carried out the roles now performed by proteins and DNA [Jeffares & Poole 2000]. There are a lot of uncertainties when we go this far back in evolutionary time and perhaps all we can be certain of is that, at a point in Earth’s history (probably over 3 billion years ago), cells emerged which stored recipes for making both proteins and RNA on a third molecule, DNA.

Nevertheless, studying LUCA is not science fiction. In the same way as humans and chimpanzees shared a common history until less than 10 million years ago, all modern lifeforms shared a common history back as far as the split that gave rise to the three ‘domains’ of life we now know of as archaea, bacteria and eukaryotes; that is, back as far as LUCA. That there are three domains was first established by Carl Woese and colleagues, who found that the group called prokaryotes was actually two groups, the archaea and bacteria [Woese & Fox 1977; Woese et al. 1990]. Amazingly, this work has largely stood the test of time, and though it is argued that there has been extensive gene swapping between these two groups [Pennisi 1998, 1999; Doolittle 1999; Eisen 2000], recent analyses using complete genomes supports Woese and colleagues’ decision to split prokaryotes into archaea and bacteria [Snel et al. 1999; Sicheritz-Pontén & Andersson 2001; Brown et al. 2001].

Anthony Poole received his Ph.D. from Massey University, New Zealand. He did a postdoc at the Allan Wilson Centre for Molecular Ecology & Evolution, before moving to Stockholm University, on a Swedish Research Council-funded Assistant Professorship, then as a Royal Swedish Academy of Sciences Research Fellow. His research to date has centered around questions in early evolution, and his current focus is on the origins of DNA and the evolution of the eukaryote cell. He is currently based at the University of Canterbury http://www.biol.canterbury.ac.nz/people/poole.shtml

My Name is LUCA—The Last Universal Common Ancestor

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The Genetic Code

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Article Images

Prokaryotic Cell: http://micro.magnet.fsu.edu/cells/bacteriacell.html
Eukaryotic Cell : http://micro.magnet.fsu.edu/cells/animalcell.html
Mitochondria: http://micro.magnet.fsu.edu/cells/mitochondria/mitochondria.html

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