Re: flying saucer

From: Loren Haarsma <lhaarsma@calvin.edu>
Date: Fri Sep 17 2004 - 14:27:10 EDT

On Thu, 16 Sep 2004, Alexanian, Moorad wrote:

> "Suppose a flying saucer arrives to earth with a living animal in it.
> The animal is quite distinct from anything we have ever seen on earth.
> How can we tell whether that animal was the result of natural selection
> that took place in a far away planet or that it was designed by the
> aliens in that planet?"

This question is interesting because, in its way, it points towards the
primary evidence for evolution on earth. But I'll come back to that
later.

  There are some kinds of evidence which would strongly favor the
hypothesis that aliens designed the animal, or at least modified its DNA.
For example: (1) If a sequence of 1024 base pairs in its non-coding DNA
corresponded exactly to the first 1024 binary digits of pi. (2) If it
exhibited a genetically programmed behavioral trait in response to
something which could not occur naturally (for example, refined metals).
(3) If it could not reproduce without intravenous injection of a several
synthetic chemicals which it could not responably obtain from its natural
environment because, for example, the chemicals are toxic to it if
injested. (Wouldn't that be a neat way to control populations of pets?)
These sorts of things would be fairly conclusive evidence.

  If the animal didn't have any such give-aways, there are some kins of
evidence which would favor the hypothesis that the animal developed via
mutation and natural select. For example: (1) If it had pseudogenes.
(2) If its genes could be sorted into homologous "gene families" which
could reasonably have been produced through evolution via gene
duplication. (E.g. red and green rhodopsin genes in primates.)
Evolution, on earth at least, produces these sorts of things.
  Of course, the aliens might have taken an "evolved" critter and tinkered
with just a _portion_ of the animal's DNA. And very crafty aliens could
create the entire DNA of the critter while making it look like it was the
product of evolution -- pseudogenes and all. So this sort of evidence,
based on a single animal, isn't conclusive.

  Which brings me back to my first point: the main evidence for evolution
comes not from looking at a single animal, but from looking at lots of
different species and seeing "nested patterns of homologies."
  Briefly, here is what I mean by "nested homologies": If you
sequence a single gene in a bunch of species, you find the genetic
sequences of closely related species are very homologous, and the
sequences of more distant species are less homologous. These patterns of
homology are "nested" -- the recur at the genus, family, order, class,
and phylum levels. The sequences in all primates are closer to each other
than they are to the sequences in rats or dogs. But the sequences in all
mammals are closer to each other than they are to the sequences in bird or
reptiles. Etc. These nested patterns of homology cannot simply be due to
"similar function" because they also occur in the non-transcribed regions
ofthe genes.
  Moreover, nested homologies are found not only in gene sequences, but
also in genomic organizations (i.e. where the genes are located on the
chromosomes), in developmental programs of organisms, in the geographic
distribution of species, and in the anatomical features of organisms.
  Moreover, the "family trees" which you construct from these patterns of
nested homologies match the family trees constructed from the fossil
record.
  All of these independent lines of evidence, taken from thousands of
different species and their fossil records, are what constitute compelling
evidence for evolution.
  Which we wouldn't have if those aliens only sent us a single animal.

Loren
Received on Fri Sep 17 15:50:07 2004

This archive was generated by hypermail 2.1.8 : Fri Sep 17 2004 - 15:50:08 EDT