Last Universal Common Ancestor
In Charles Darwin’s (1) The Origin of the Species, published in 1859 he posited the
theory of evolution on which our modern understanding of the nature of life on earth is
based. In this treatise, (2) it speculated that all life forms on this planet, from humans to
hermit crabs to single-cell organisms, likely evolved, over the course of millennia, from a
single, primordial common ancestor. This speculation was the seed of an idea that
twentieth and twenty-first century scientists eventually expanded into the notion of the
Last Universal Common Ancestor (LUCA).
 From a (3) layman perspective, it might seem impossible that the (4) small diversity of
terrestrial life could share a single origin.  In fact, earth’s biodiversity is so (5) extreme that its
creatures have been taxonomically subdivided into six distinct kingdoms based on shared
characteristics.  But despite the significant differences between these kingdoms, each finds its
origin in a common ancestor.  This common ancestor, defined by scientists as the (6)
recentest shared ancestor of these wildly disparate life forms, is the organism known as
LUCA.  It is generally agreed that this organism likely existed between 3.5 and 3.8 billion
years ago, (7) and until recently, scientists had been unable to do more than speculate about
what LUCA might have looked like, or what kind of environment it might have inhabited. (8)
In 2016, however, LUCA enjoyed a renewed spate of international attention after Dr.
William Martin, a German evolutionary biologist, published a study identifying 355 shared
bacterial and archaeal gene families that, (9) looking up his research, could be traced back
to LUCA. Dr. Martin identified these gene families by analyzing thousands of microbial
gene sequences consisting of millions of individual genes in order to identify which
widespread genes had likely been passed down from a remote common ancestor. This
study analyzed genomic patterns among bacteria and archaebacteria because modern
scientists generally believe that these kingdoms predated eukaryotic kingdoms.
The result of Dr. Martin’s genomic analysis was a tentative portrait of LUCA. Based on the
genes likely passed down by LUCA, Dr. Martin suggested that (10) LUCA lived in an
unoxygenated habitat, and that the organism probably feeds on hydrogen gas. (11) However,
Dr. Martin hypothesized that LUCA probably lived near deep-sea hydrothermal vents, a
theory that aligns with some previously held theories about the origin and development of
life on earth.
Dr. Martin has received some pushback from peers, though, especially as a result of one
further (12) guess produced in his study. Dr. Martin has suggested that LUCA might (13)
be either the closest common ancestor of earth’s many species or
one of the very first life forms to inhabit the planet, period. This, some scientists have
argued, is a precipitate and as-yet unfounded claim, especially because of its broader
implications: scientists have long-argued about whether life on earth more likely originated
in shallow pools of water on land, with the aid of UV rays (14) from the sun; or in the deep, dark,
hydrogenated atmosphere of underwater volcanoes. Much more research will have to be
done before scientists reach a consensus about whether Dr. Martin has indeed successfully
profiled LUCA, or about how many life forms, and of what nature, predated this infamous
Created for Albert.io. Copyright 2016. All rights reserved.
From a (4) laymen's perspective, it might seem impossible that the small diversity of terrestrial life could share a single origin.