Tuesday, May 12, 2009

How Do Different Species Arise?

An Idea on Evolution and Species Differentiation

I will start with the primeval ocean full of stuff and at some moment a piece of replicating DNA appears.
The first question is: Why did the stuff in the ocean combine to make something that was self replicating? I don’t know and when looking for a book to read I never choose biochemistry. I take the fact that we are here as prima facie evidence that it did happen.
Here I am making the assumption that life started as a very simple organism. This is contrary to the creationist point of view that man was created fully made some thousands of years ago.
I don’t see why more than one piece of DNA would appear but I see no reason that they couldn’t appear in a volume of ocean or even throughout the ocean. This mass appearance seems very unlikely to me.
I will suppose that just one appears. It seems to me that there would be just one primordial piece of DNA but that is more for aesthetic reasons than logical reasons.
It doesn’t really make any difference. For my argument to hold, the pieces just had to be small. After a fairly “short time” there would be so many pieces of DNA that the original number of pieces would be seen as a point.
The piece of DNA had no predators because it hadn’t previously existed to develop any. But it could have happened that there were killer molecules. If a killer molecule accidently bumped into a piece of DNA they might have combined in such a way as to ruin the DNA’s reproductive ability. I suppose a piece of DNA could have been destroyed if it was hit by lightening. I suppose there were a lot of ways a piece of DNA could have met an unreproductive end.
The presence of life as we know it implies that the DNA population grows faster than the DNA is annihilated so after a certain amount of time, the doubling time, the DNA population effectively doubles.
Since the population is pretty homogeneous in the beginning I’m going to model the early growth process as starting with one piece of DNA and that an individual doubles after a length, T, of time; T is the doubling time. Early on T is fairly constant.
I assume that the time estimates of science are in the ballpark so I’ve got three billion years to fool around with.
How many times will the population double in a million years? If it takes a thousand years for a population to double, so for example it takes a thousand years for the first piece to double, then in a million years there will be 21000 individuals. This is on the order of 10300 individuals. If a grain of sand was 1/64 inch on a side, 1060 of them would fill the universe.
Clearly the population of pieces of DNA doesn’t double a thousand times in a million years but after a million years there must have been a lot of DNA floating around.
Now I come to my point which depends only on the fact that there is a growing population of DNA pieces and that, since the pieces are small, there are significant mutations that are replicated.
At this early time a mutation of a piece of DNA would involve a significant part of the piece and would thus change it quite a bit. One gene changing out of thousands is different than one gene changing out of a few.
My point is that the differentiation of species starts here. The mutations initiate changes that lead to different species.
When the organisms get larger, mutation is followed by natural selection. The mutations do not give rise to a new species, they change the phenotype; the feathers of Darwin’s finches get darker but they are still finches.
Different species can trace their ancestry back to one of the early mutations of DNA and hence back to the primordial piece of DNA.

I have always wondered about the origin of life. I had this picture of DNA appearing all over the primordial ocean and this seemed odd. But then I thought that, because of exponential growth and in particular doubling, you only need to start with one self-replicating piece of DNA.
I have also always been bothered by the appearance of different species. I can’t see how that could happen. Breeders can develop very different dogs but haven’t come up with a new species.
If you start with an ape, how does it mutate into a human? Does a whole bunch of apes become a whole bunch of humans? Does one ape change a little bit and some how start the path to humanity?
So apes with bigger heads are chosen for? So what?
Why can’t small heads think? Computer chips get smaller every day and “think” better. Not that I think you can model the human brain as a computer.
If I assume that species were differentiated soon after DNA appeared these problems go away.
It seems to me that a mutation of an early piece of DNA, a very small piece of DNA, could make a big difference in the end result of that piece of DNA. The end result is sensitive to initial conditions.
I don’t think that the random mutations to apes change the outcome of the succeeding apes much. The end result is a change in phenotype but not a change in species. The more complex the organism, the less sensitive it is to initial conditions. Mutation gives rise to a change in phenotype but not species.
Early DNA changes from chaotic evolution to non-chaotic as the DNA becomes more complex, like being an ape.

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