From: Gennady Ra (anyservice@cris.crimea.ua)
Date: Mon Jul 29 2002 - 02:58:35 MDT
At 11:03 AM 07/28/2002 +1000, you Brett Paatsch wrote:
>In his book The Darwinian Wars, (1999), Andrew Brown, described the fall
>into depression and ultimately suicide (in 1974) of theoretcial biologist
>George Price. According to Brown, (Price. something of a mathematical whiz)
>"reformulated a set of mathematical equations that shows how altruism can
>prosper in aworld where it seems that only selfishness is rewarded. The
>equations had been discovered ten before by (William) Hamilton, but Price's
>reworking was more elegant and of wider application. He had provided a
>general way in which to measure the direction and speed of any selection
>process; this makes possible, in principle, a Darwinian analysis of almost
>anything." (Price waas shocked by his discovery) for although his equation
>showed that truly self-sacrificing behaviour can exist among animals, and
>even humans, it seemed to show that there is nothing noble in it. Only
>behavior which helps to spread the genes that cause it can survive in the
>very long term.
An interesting quote from Britannica's article on evolution. Note especially
the extreme honeybee example.
===================
Kin selection
The apparent altruistic behaviour of many animals is, like some
manifestations of sexual selection, a trait that at first seems incompatible
with the theory of natural selection. Altruism is a form of behaviour that
benefits other individuals at the expense of the one that performs the
action; the fitness of the altruist is diminished by its behaviour, whereas
individuals that act selfishly benefit from it at no cost to themselves.
Accordingly it might be expected that natural selection would foster the
development of selfish behaviour and eliminate altruism. This conclusion is
not so compelling when it is noticed that the beneficiaries of altruistic
behaviour are usually relatives. They all carry the same genes, including
the genes that promote altruistic behaviour. Altruism may evolve by kin
selection, which is simply a type of natural selection in which relatives
are taken into consideration when evaluating an individual's fitness.
Natural selection favours genes that increase the reproductive success of
their carriers, but it is not necessary that all individuals with a given
genotype have higher reproductive success. It suffices that carriers of the
genotype reproduce more successfully on the average than those possessing
alternative genotypes. A parent shares half of its genes with each progeny,
so a gene that promotes parental altruism is favoured by selection if the
behaviour's cost to the parent is less than half of its average benefits to
the progeny. Such a gene will be more likely to increase in frequency
through the generations than an alternative gene that does not promote
altruistic behaviour. Parental care is, therefore, a form of altruism
readily explained by kin selection. The parent spends some energy caring for
the progeny because it increases the reproductive success of the parent's
genes.
Kin selection extends beyond the relationship between parents and their
offspring. It facilitates the development of altruistic behaviour when the
energy invested, or the risk incurred, by an individual is compensated in
excess by the benefits ensuing to relatives. The closer the relationship
between the beneficiaries and the altruist, and the greater the number of
beneficiaries, the higher the risks and efforts warranted in the altruist.
Individuals that live together in a herd or troop usually are related and
often behave toward each other in this way. Adult zebras, for instance, will
turn toward an attacking predator to protect the young in the herd, rather
than flee to protect themselves.
Altruism also occurs among unrelated individuals when the behaviour is
reciprocal and the altruist's costs are smaller than the benefits to the
recipient. This reciprocal altruism is found in the mutual grooming of
chimpanzees and other primates as they clean each other of lice and other
pests. Another example appears in flocks of birds that post sentinels to
warn of danger. A crow sitting in a tree watching for predators, while the
rest of the flock forages, incurs a small loss by not feeding; but this is
well compensated by the protection it receives when it itself forages and
others of the flock stand guard.
A particularly valuable contribution of the theory of kin selection is its
explanation of the evolution of social behaviour among ants, bees, wasps,
and other social insects. In the honeybee, for example, the female workers
build the hive, care for the young, and gather food, but they are sterile;
the queen bee alone produces progeny. It would seem that the workers'
behaviour would in no way be promoted or maintained by natural selection.
Any genes causing such behaviour would seem likely to be eliminated from the
population, because individuals exhibiting the behaviour do not increase
their own reproductive success, but that of the queen. The situation is,
however, more complex.
Queen bees produce some eggs that remain unfertilized and develop into
males, or drones, having a mother but no father. Their main role in the
colony is to engage in the "nuptial flight," during which one of them
fertilizes the queen. Other eggs laid by queen bees are fertilized and
develop into females, the large majority of which are workers. A queen
typically mates with a single male once during her lifetime; the male's
sperm is stored in the queen's spermatheca, from which it is gradually
released as she lays fertilized eggs. All the queen's female progeny
therefore have the same father, so that workers are more closely related to
one another and to any new sister queen than they are to the mother queen.
The female workers receive one-half of their genes from the mother and
one-half from the father, but they share among themselves three-quarters of
their genes. One half of their genes come from the father; this half of the
set is the same in every worker, because the father had only one set of
genes rather than two to pass on (the male developed from an unfertilized
egg, so all his sperm carry the same set of genes). The other half of the
workers' genes come from the mother, and on the average half of them are
identical in any two sisters. Consequently, with three-quarters of her genes
present in her sisters but only half of her genes able to be passed on to a
daughter, a worker's genes are transmitted one-and-a-half times more
effectively when she raises a sister (whether another worker or a new queen)
than if she produces a daughter of her own.
Copyright © 1994-2001 Encyclopaedia Britannica, Inc.
=======================
Gennady
Simferopol Crimea Ukraine
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