From:
RRC
Date: 2001-06-02 06:53:00 UTC
Subject: Bob C: Persistent Albinism
As I argued earlier, persistent albinism is a proof of domestication
because it doesn't exist in wild animal populations. I think it was
Linda who mentioned a subset of squirrels in her region which included a
number of albinistic individuals, and wondered if that might be an
exception. The answer is no.
As with anything pertaining to domestication or evolution, the key is
selection. Albinism does not persist in wild animal populations which
are unregulated by humans; that is, governed by natural selection. This
is not the case in most instances within areas regulated by humans
because of the selective removal of most predators, especially those
that hunt during the daytime. I suspect the reason albinism is seen in
these squirrels is because most of the daytime predators, including
raptors, do not exist in great enough numbers to exert a strong enough
selective force on the population in question. What predators that exist
might well be feeding on albinistic squirrels at a much higher rate than
naturally colored ones, which would normally eliminate the trait from
the population, but because daytime predators are so few in number, they
have little or no impact at the population level and the trait persists.
Remember, most squirrels are diurnal, and in areas of even minor human
impact, remaining predators tend to be nocturnal or crepuscular to avoid
human interactions. Also, daytime predators have either been hunted out,
or have had such a disruption of their food base that they cannot exist
in large numbers. Regardless, in urban, suburban or rural areas which
are regulated by humans, a species may be impacted to such a degree that
normal rules of selection may not seem to apply, and traits such as
albinism can persist for unusually long periods of time. Rather than die
from predation, in predator-free environments, most individuals die from
disease, accidents, housecats, and humans. In these cases, albinism,
especially in a small founding population, can (and does) become
established and can persist, even in animals which are considered wild
(the opposite is also true, with melanistic [dark] individuals
persisting in a population naturally selected for lighter coloration).
But place those same individuals in an environment filled with hungry
predators, and in a short time you will find the number of albinistic
individuals has markedly declined.
Remember, we are speaking of a human controlled environment, which
isafter allwhat rural, urban and suburban areas are. And don't be
fooled by farm land; most rural areas are so monocultural that they
support less species diversity and richness than inner city parks. Those
vast wheat and corn fields have less species than most sand deserts.
Almost all mammalian extinctions are the direct result of agricultural
practices, followed by overhunting/fishing and urbanization.
Albinism is not an easy trait to breed into a population. It is
recessive, so you need two copies for expression, which means you either
need more than one individual having independent mutations, OR you need
a lot of old fashioned southern inbreeding. The mutation resulting in
albinism is fairly common in species, so it is not all that unlikely
that multiple independent mutations can take place and random breeding
can ultimately result in the expression of the trait. But in the case of
ferrets (and other domestic animals), the trait was probably first
expressed as a result of inbreeding, and it was certainly conserved
because of it. What this means is, the chances are pretty good that the
albino trait in ferret is the result of a single, chance mutation, and
all albino ferrets are more or less distant cousins. This type of
inbreeding is a result of domestication, pure and simple. Humans saw it,
humans liked it, and humans bred it in to such a degree that it is now a
persistent trait. A similar thing is happening with the squirrels,
except instead of humans seeing it, liking it and breeding for it, what
is happening is that an initial small population of squirrels was freed
from selective pressures for coloration by human removal of local
predators, and a chance mutation was conserved within the population.
It is like why men go bald. Baldness doesn't seem to increase or
decrease human fitness, so why did it become a trait and why does it
persist? The chance mutation became a trait long ago (prior to human
global dispersal) and was inbred into the founding population which
ultimately became humans. Since it doesn't seem to increase or decrease
human fitness, it is not under selective pressure, so it persists (there
are some who argue baldness is a gender recognition trait and is under
sexual selection, but the idea is very controversial and not generally
accepted). The same thing is occurring with the squirrels; a chance
mutation for albinism was inbred into a small founding population,
living under human dominion, and because selective pressures no longer
exist because of human predator control, the trait persists.
In other words, in both cases, albinism exists because of human action.
In the one case, it is proof of human predator control, and in the
other, of domestication. In both cases, it proves human involvement.
Bob C