Wednesday, February 22, 2006

Survival strategies

Evidence 1 :- A plant's seed whose pod can float in water for months, lies dormant for years until conditions that are just right precipitate germination. To a scientist, it is evidence of survival strategy. A plant can colonise a new area far away from its original base.

Evidence 2 :- A bacterium or other organism can withstand being frozen in a vacuum indefinitely until jolted back into life when it hits, say a planet. To a scientist this is irrelevant detail and doesn't indicate that certain bacteria have evolved this feature so they can go planet-hopping when major collisions happen.

4 comments:

Dr. Clam said...

The important thing to remember is that both of these cases are speculation. A plant’s seeds may acquire the tolerance to salt water that allows it to cross long stretches of open ocean because it gives it a slight competitive advantage with its neighbours in a brackish swamp. Bacteria may acquire the abilities that allow them to survive in space because it gives them a competitive advantage under terrestrial conditions of furious competition.

We know as well as we know anything that life has been around a long, long, time, that it has been continually changing over that period, that it is all related, and that some species are more related than others, which can be quantified by looking at the genetic material of the wee beasties. Anyone who denies this is one with the homeopaths, and ought to be anathematized.

Everything beyond this is legitimate grounds for discussion and it is unscientific to castigate the purveyors of alternative models as unscientific. How did life arise? How do useful variations arise? How are these propagated through a population?

Natural selection is an obvious mechanism for the propagation of useful traits, and it is likely enough that it can explain everything. However, almost all of our direct experience has been with ‘Unnatural Selection’ directed by intelligent beings. We cannot say dogmatically that our experiments with dogs and pigeons and sheep etc. are not echoes of earlier projects by earlier intelligences.

Copying errors and stray radiation can certainly generate random genetic changes. These have apparently given rise to the genetic drift that allows us to tell how closely things are related to other things. (Parenthetically, if it is assumed that genetic drift occurs at a constant rate, you can take any of the little charts appearing in biology textbooks and extrapolate it back to get a date much older than that of the formation of Earth for the beginning of life.) Genetic drift occurs mainly in ‘junk DNA’ or in non-vital sequences of DNA where heritable changes make no difference to the function of the proteins they encode. It is likely enough that random genetic changes can give rise to beneficial mutation. But to my knowledge, no one has ever seen a beneficial mutation introduced by random mutation in the laboratory. I may be ignorant, but here is the experiment: it is observed that baby fruit fly has a better resistance to paparazzi flashbulbs than daddy fruitfly and mummy fruit fly. We individually homogenize the fruit-fly family, sequence their DNA, and find one base pair in one gene coding for a protein involved in flash-bulb resistance that is different. Of course this is not the only way for beneficial variations to arise. We now know a very good way to generate new and beneficial traits. It is called horizontal gene transfer and we do it all the time. We don’t know how often it occurs in the natural world, and we cannot say dogmatically that we are the first intelligence to apply it intelligently to life on Earth.

We have found traces of life in the oldest sedimentary rocks available to look for life in. A few hundred million years of ambiguity does translate into a lot of time for life to appear by slow stages on Earth itself, but this contrasts oddly with the following three billion years in which precious little seems to have changed in the fossil record. We don’t know for certain that the fossil life we see then was even related to us: I don’t think we can say with any confidence ‘here is something that looks like a relative’ until the Cambrian.

Finally, our historical experience has been that everyone who has said: ‘I can explain all features of the observable universe in terms of mechanisms we understand now’ has been wrong.

I thought I would be fairer to make a really long comment here instead of kidnapping this discussion back to my blog. :)

Marco said...

Suffice it to say that what evidence there is, life seems to predate the formation of the Earth, bacteria therein would seem to be able to survive planetary transfer, and large collisions causing such transfer were commonplace in the early earth. Put together, these indicators demonstrate that A) Earth is not the primary origin. B) Bacteria almost certainly exists on other planets/moons of the solar system, and C) Analysis of extra-terrestrial bacteria would give us more indicators in this regard.

Dr. Clam said...

I agree! I guess I was just monolguing for the folks at home.

Dr. Clam said...

#1: When will Marco post again
In thunder lightning, or in rain?

#2: When the hurlyburly's done,
When the battle's lost and won.

#3: That will be ere the set of....?