[ExI] The Unique Merger
pharos at gmail.com
Mon Feb 10 23:56:29 UTC 2014
A great explanation of the story of life creation.
The Unique Merger That Made You (and Ewe, and Yew)
All sophisticated life on the planet Earth may owe its existence to
one freakish event.
Still, without the eukaryotic architecture, bacteria are forever
constrained in size and complexity. Sure, they have their amazing
skill sets, but it's the eukaryotes that cover the Earth in forest and
grassland, that navigate the planet looking for food and mates, that
build rockets to Mars.
The transition from the classic prokaryotic model to the deluxe
eukaryotic one is arguably the most important event in the history of
life on Earth. And in more than 3 billion years of existence, it
happened exactly once.
If this story is true, and there are still those who doubt it, then
all eukaryotes--every flower and fungus, spider and sparrow, man and
woman--descended from a sudden and breathtakingly improbable merger
between two microbes. They were our
great-great-great-great-...-great-grandparents, and by becoming one,
they laid the groundwork for the life forms that seem to make our
planet so special. The world as we see it (and the fact that we see it
at all; eyes are a eukaryotic invention) was irrevocably changed by
that fateful union--a union so unlikely that it very well might not
have happened at all, leaving our world forever dominated by microbes,
never to welcome sophisticated and amazing life like trees, mushrooms,
caterpillars, and us.
In 2004, James Lake changed the rules of engagement. Rather than
looking at any single gene, he and his colleague Maria Rivera compared
the entire genomes of two eukaryotes, three bacteria, and three
archaea. Their analysis supported the merger-first ideas: They
concluded that the common ancestor of all life diverged into bacteria
and archaea, which evolved independently until two of their members
suddenly merged. This created the first eukaryotes and closed what now
appeared to be a "ring of life." Before that fateful encounter, life
had just two major domains. Afterward, it had three.
This improbability has implications for the search for alien life. On
other worlds with the right chemical conditions, Lane believes that
life would be sure to emerge. But without a fateful merger, it would
be forever microbial. Perhaps this is the answer to the Fermi
paradox--the puzzling contradiction between the high apparent odds that
intelligent life would exist elsewhere among the billions of planets
in the Milky Way, and our inability to find any signs of such
intelligence. As Lane wrote in 2010, "The unavoidable conclusion is
that the universe should be full of bacteria, but more complex life
will be rare."
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