Re: new method of evolutionary change

David Campbell (bivalve@mailserv0.isis.unc.edu)
Tue, 15 Dec 1998 15:55:52 -0400

Robin Mandell asked for clarification of my message...
>Hi Dave Cambell,
>Do we know which is more likely? The + or the - ?_

For small changes, positive and negative effects are probably about equally
likely. Large mutations are more likely to be negative, but if times are
very hard, a high rate of mutation may actually be helpful. This is
observed in cancer cells and in the high mutation rate observed in bacteria
given a sugar they could not normally digest.

>>A more dramatic way to build up genetic information is to duplicate part of
>>the genome. This can happen by unequal crossing over during meiosis or by
>>hybridization (common in plants, rarer in animals), among other methods.
>>As a result, the organism has extra copies of genes. As long as one stays
>>functional, mutations in another copy may provide novel functions.
>>
>Is there an example of this today? Talk down I am on the edge of not really
>getting 1/2 of this.

In plants, hybridization often leads to the production of a new species
with an extra set of genes. Many agriculturally important species have
this, including wheat, corn, at least some species of cotton, and most
seedless fruit (including bananas). It has been done deliberately in the
lab (a Soviet scientist crossed cabbage and raddish and got a useless
vegetable with cabbage roots and raddish leaves, for example), and also
happens naturally. Another well-studied example is the marsh grass
Spartina in England, where the native species has hybridized with some
introduced from the U.S. Among animals, there are lizards in which hybrids
are parthenogenic females, recognized as a distinct species. Comparing the
amount of DNA and number of copies of genes in different species suggests
that the vast majority of new species of plants may arise in this way. A
plant with a strange number of chromosomes can start a population by
asexual reproduction or by self-fertilization, but fewer animals are able
to do these, and so it happens more rarely in animals. However, there are
a few points in animal evolution where the amount of DNA has about doubled
and the number of copies of certain genes has increased.

More frequently, there are many gene families that appear to have arisen by
unequal crossing over or other duplication of a small part of the genome.
A particular example involving color vision in monkeys has been
well-studied. Normally, this species is colorblind. A simple mutation
changes the type of color blindness. If a normal and a mutant breed, the
offspring will have both genes and color vision. Unequal crossing over can
then put the two on the same chromosome, so that full color vision (by
primate standards) is now coded by two genes rather than different versions
of the same gene.

>Do you think the big jumps in life were sudden or slow and gradual?

Probably some of both. The transition between reptiles and mammals, for
example, took place by many small steps over tens of millions of years.
However, mutations in genes that affect development can produce drastic,
immediate changes.

>Do you see it as all natural or was God directly manipulating things?

I think God directly controls everything. For example, He is no less
involved if I let go of a rock in midair and it falls to the floor than if
it were to remain hovering without support. The vast majority of the time,
He follows certain patterns in how He runs nature. These patterns are what
we try to describe as natural laws. Miracles are when He does not follow
these patterns because of some more important factor, such as revelation of
His nature to humans. I do not see any particular evidence that He did not
stick with patterns in the process of creeating life. The evidence neither
requires nor rules out miracles in the process, but He seems to use them
only when necessary, and I do not believe that they were needed for
physical creation, except at some point in the very beginning when creation
was started. I do not know enough physics to guess at what point this
beginning would have been.

>What do you think of the probability of life from non life by chance?

"Chance" is a word to reagrd with suspicion in this context.
Mathematically, there are some things that we cannot predict except by a
general statement based on the laws of probability. These may be referred
to as random in a technical sense. Some aspects of evolution, as far as we
can tell, are mathematically random.

However, in a more informal sense, chance can refer to a lack of oversight.
According to the Bible, God is sovereign over mathematically random things
such as casting lots, and over everything else. Thus, there is nothing
that is truly chance in the sense of beyond God's oversight. (Obviously,
people debate exactly what the role of free will is, but I think most
people would agree that primordial soup does not have much will).

I think God probably created life from non-life without using miracles,
because He seems to use them quite sparingly and because I do not see an
unbridgeable gap. However, there is not enough evidence to be sure.

David C.