Tuesday, October 24, 2006

Of Neanderthals and Microbes

The capacity to blunder slightly is the real marvel of DNA. Without this special attribute, we would still be anaerobic bacteria and there would be no music. ~Lewis Thomas

How about a couple of disparate comments on the subject of life?

Neanderthals continue to be hot stuff these days. I recently summarized some of the current findings, but, with these cave folks being so popular at the moment, it's hard to keep up. Most recently, a new DNA analysis has determined that Neanderthals and modern humans are, in fact, completely different species, probably sharing a common ancestor. In fact, Neanderthals has more closely related to chimps than to us.

I don't know that it comes as a huge surprise or disappointment to people that we aren't more closely related to the archetypal caveman. It has been clear for some time that Neanderthal's brain was wired differently than ours, if only based on his lack of change over a few hundred thousand years. It's not known for certain whether he could speak as we do. His brain is physically different from ours. He was a human species to be sure, but he wasn't part of our species.

Yet, I always sense some disappointment on the part of researchers when they discover that the gap between modern humans and Neanderthal is yet greater than we previously thought. There have been scientists who have held out hope for proof of interbreeding between the two species. While there may have been, there's no evidence of any propagation of mitochondrial DNA that contains Neanderthal elements. When the last of the cavemen passed on, there was no biological bequest to us.

I think many people are still bothered by the thought that our ancestors might have hastened the demise of these intriguing people. While homo sapiens might well have played a role in the end of the elder species, it is fairly well established that the Neanderthals were in serious decline before the two groups met 40,000 years ago. Perhaps this decline was due to climate change, although evidence suggests that climate variation occurred several times during the caveman's duration on the planet. It does appear, though, that by the time the last ice age would down, Neanderthals were particularly suited to the harsh conditions. When the game patterns began to change, the Neanderthals did not adapt well. And apparently, they didn't compete well with the Cro-Magnons.

How we got to be what we are has been an overriding question for human beings. We have searched our own planet for the history of life, and we search other planets for signs that life as we know it exists or has existed.

Thanks to a veritable fleet of satellites and rovers busily investigating the red planet, we have some very good ideas about whether water ever existed on Mars. All the signs point to the existence of liquid water at one time, but the search for currently available water has so far come up empty. It's thought that there might be considerable water frozen in the sands of Mars, and at least two of the satellites have devices designed to detect it. Those searches are in their early stages.

Now, water on Mars is important for a couple of reason. First, if we ever hope to colonize the planet, a source of water is a necessity. We can hardly hope to establish settlements if we have to haul life's major necessity with us. By the way, previous reports of water ice "ponds" on our Moon appear to have been erroneous, dashing hopes of having an easy source of water for lunar bases. Space colonization is just not going to be simple.

But there's another reason that we would love to find water on Mars.

If there is still some microbial life on the planet, it would most likely need water to survive. The Viking landers sent back ambiguous evidence of the possibility of little bugs existing in the Martian sands, though I think most scientists think that the experiments that indicated life were probably generating false results. But, the possibility exists.

Finding life on Mars would help us find out a little more about how we might have come to be. Europa holds promise of water and possible life, but finding it is a major challenge. The ice might be a mile thick, so aside from all the difficulties of getting a probe all the way to the Jovian system, having it survive the radiation, and land safely, once it gets down it has to bore through the ice, do some science and get the information back to Earth. Oh, and it can't contaminate the moon with Earthly bacteria.

Piece of cake.

Of course, we're taking a detailed look at a laboratory that approximates early Earth: Titan. Saturn's moon has conditions that might have existed before our world became oxygenated, with it's reducing atmosphere raining methane on the surface. There are even those who think that there could conceivably be some sort of proto-life hiding in the mists of Titan.

But, generally speaking, you need some sort of solvent to get chemical reactions working that would generate even proteins. On Earth, we have water (there's that word again). On Titan, it was thought we would find ocean's of methane. Unfortunately, Titan appears to be relatively dry.

To say that scientists have been disappointed by the lack of methane seas is probably putting it mildly. I am reminded of how badly scientists wanted to find that Venus was covered by oceans. When it was found to be hellishly hot, there was a sense of a huge letdown.

It's not that they haven't found any liquid on Titan. It appears that there are transient lakes of methane near the north polar region of the moon. I say "appears" because the lakes have only been imaged by radar, but, at this point, the only explanation for the dark splotches is that they are a liquid surface. But, it appears that our ideas of Titan's chemistry need some reworking.

Interestingly, every time we turn around, we find life in places on Earth where it shouldn't be, like in mines where there's no sunlight or, more famously, around thermal vents in the depths of our own oceans. Life also is more tenacious than we can imagine. Nothing can be better proof of this than the microbes that were found on materials brought back by lunar astronauts from an old Surveyor satellite on the Moon. These were contamination from Earth that got onto the satellite prior to launch (despite efforts to avoid such contamination). The little boogers were subjected to radiation, huge temperature variations, and the near vacuum of space, yet scientists were able to resuscitate the microbes once they were returned to Earth.

It's no wonder we think we might find bugs on Mars, fish on Europa, or methane-munching microbes on Titan. Life is tenacious and pernicious, despite the many vicissitudes that it faces. Once it gets to an advanced stage like, say, being a Neanderthal, it gets more fragile. But at the earliest stages, it takes a lot to prevent life from taking hold. Maybe that's why we're so interested in our fellow species and in extraterrestrial life. If we can find out what did in the former, we might be able to avoid extinction ourselves. If we can find life elsewhere, then we can better understand the survival mechanisms that allow bacteria to make it in extreme conditions.

Either way, we might increase our own odds of survival.

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