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Posts Tagged ‘space exploration’

None of these things is just like the others

In my previous post, I explored convergent evolution: when two different species, usually separated by distance, evolve a similar physical characteristic independently of each other. At the end of the post, I said that I would follow up with a post on the far more common divergent evolution.

Simply put, divergent evolution is when two groups of the same species evolve differently. The environments in which the groups live are the most common cause of divergent evolution – in other words, if two groups of the same species are separated into different environments, they will each evolve and adapt separately to fit the environment they’re in. Arguably the most famous example of divergent evolution is Darwin’s finches, which he described in On the Origin of Species:

“The inhabitants of the Cape de Verde Islands are related to those of Africa, like those of the Galapagos to America. I believe this grand fact can receive no sort of explanation on the ordinary view of independent creation; whereas on the view here maintained, it is obvious that the Galapagos Islands would be likely to receive colonists, whether by occasional means of transport or by formerly continuous land, from America; and the Cape de Verde Islands from Africa; and that such colonists would be liable to modification;—the principle of inheritance still betraying their original birthplace.”

- On the Origin of Species, Chapter XII: Geographical Distribution. Charles Darwin, 1859

The “inhabitants” Darwin refers to in the above passage are the variations of finches. (It’s interesting to note that, since Darwin was developing the very concept of evolution, he didn’t have a word for it to utilize – instead referring to it as “modification”.)

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You Only Find What You’re Looking For

Author’s Note: This is the first SiMF post picked up for reprinting by io9 — I know it will be the first of many!

Extraterrestrial life is a staple of SF and the focus of astrobiology and SETI.  Yet whereas SF has populated countless worlds with varying success, from Tiptree’s haunting Flenni (Your Haploid Heart) to Lucas’ annoying Ewoks, real ETs remain stubbornly elusive: nobody has received a transmission demanding more Chuck Berry, and the data from the planetary probes are maddeningly inconclusive.  Equally controversial are the shadowy forms on Martian asteroid ALH84001, although the pendulum has swung toward cautious favoring of the biological possibility after scientists discovered nanobacteria on earth and water on Mars.

In part, we’re hobbled by the limits of our technology, including the problems of sample contamination and method-specific artifacts.  But we’re also severely limited by having a single life sample.  Despite its dizzying variations in form and function, extant terrestrial life arose from one source.  We know this because our genetic blueprint and its associated molecular machinery are identical across the three domains (archaea, eubacteria, eukarya).  So to be able to determine if something is alive, we need to decide what is universal and what is parochial.  We stumble through redefinitions each time our paradigms shift or our techniques achieve higher resolution.  Worse yet, our practices lag considerably behind our theories.

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