What is the Last Universal Common Ancestor (LUCA)?
The last universal common ancestor (LUCA) is a hypothetical ancient microbe from which all present-day life descends. About 60,000 years ago, there lived a human in Africa from which all living humans descend. The LUCA is an idea based on a similar principle, but being the common ancestor of all life rather than just humans. The LUCA is believed to have lived between 3.6 and 4.1 billion years ago. Life may have existed for 100-500 million years before the LUCA appeared. The LUCA is not the first living thing ever or the most primitive possible living organism, just the universal common ancestor of all extant organisms. Although fossils from the period are scant and highly degraded, we can extrapolate characteristics of the LUCA by seeing what features all of life has in common today. This includes a genetic code based on double-stranded DNA, including four nucleotides, making up 64 possible three-nucleotide codons. This selection of nucleotides is arbitrary but universal to all earthly
The issue-focused, peer-reviewed article discusses how LUCA, the last universal common ancestor, is still an enigma but scientists have been able to: find more answers in the genetic code, revise and reconstruct evolutionary trees, and understand more about the role of gene swapping in evolution. A comprehensive, original paper on LUCA by A.M. Poole is also provided as a supplement to this more general article, suitable for graduate and undergraduate teaching as well as professional scientists, at http://www.actionbioscience.org/newfrontiers/poolepaper.html.
