On Dec 29, 4:45 am, "Chris Jenkins" <[email protected]>
wrote:
> Survival of the fittest is indeed commonly misunderstood, most especially
> when it comes to humans. It's not survival of those most fit to survive.
> It's survival of those most likely to procreate, and so it has been through
> out all of evolution.
Actually it is those who are able to produce successful offspring in
their given environment.
Procreation is not enough in itself.
> And so it is that those with nought else to do but rock the bedposts turn
> out children at three times the rate... ;)
>
> On Sun, Dec 28, 2008 at 11:30 PM, archytas <[email protected]> wrote:
>
> > The phrase "survival of fittest" is widely misunderstood Many wrongly
> > assume it means that evolution always increases the chances of a
> > species surviving. Evolution sometimes results in individuals or
> > populations becoming less fit and may occasionally even lead to
> > extinction.
>
> > There are several ways in which evolution can reduce the overall
> > fitness of individuals or of populations. For starters, natural
> > selection can take place at different levels - genes, individuals,
> > groups - and what promotes the survival of a gene does not necessarily
> > increase the fitness of the individuals carrying it, or of groups of
> > these individuals.
>
> > For example, parasitic DNA elements, or transposons, can spread
> > through a population even though they make their host organisms less
> > fit. Transposons are one cause of genetic diseases such as
> > haemophilia.
>
> > Similarly, selfish individuals may thrive at the expense of altruistic
> > individuals in a group - making them the "fittest" - even though they
> > make the group as a whole less competitive. Such cheaters can have
> > disastrous consequences.
>
> > In 1932, J. B. S. Haldane suggested this could even lead to the
> > extinction of populations - a phenomenon called evolutionary suicide.
> > Models and some experimental evidence suggest he was right.
>
> > For instance, when nutrients run low, individual myxobacteria (slime
> > bacteria) may come together to form a fruiting body to produce spores.
> > Lab studies have shown that cheating myxobacteria that only produce
> > spores and never help form the non-spore producing parts of the
> > fruiting body can drive populations to extinction.
>
> > Genes capable of driving populations to extinction might have a
> > practical use, however. Biologists are exploring the possibility of
> > releasing engineered parasitic DNA into populations of malaria-
> > carrying mosquitoes.
>
> > There is concern that something similar could happen accidentally.
> > Fish that have been genetically modified to produce a growth hormone
> > grow faster and larger, mature earlier and produce more eggs. But they
> > are less likely to survive in the wild than unmodified fish. According
> > to the Trojan gene hypothesis, a gene variant that produces such
> > characteristics could spread rapidly through a wild population despite
> > reducing individual fitness, and eventually drive the population to
> > extinction.
>
> > Another way in which evolution can reduce a species' chances of
> > survival is through the accumulation of detrimental mutations.
> > Mutations provide the vital raw material for natural selection, so if
> > the mutation rate is too low a population will not be able to evolve
> > fast enough to keep up with environmental changes.
>
> > If, on the other hand, a population's mutation rate is too high,
> > detrimental mutations may accumulate faster than natural selection can
> > eliminate them. Eventually, the number of mutations can exceed the
> > "error catastrophe threshold", again leading to the extinction of a
> > population.
>
> > In theory, any species with a very small population could accumulate
> > deleterious mutations faster than it can eliminate them. The problem
> > is especially severe for asexual organisms such as the Amazon molly -
> > an effect known as Muller's rachet.
>
> > It is far less of a problem for sexually reproducing species because
> > the exchange of genetic material between chromosomes can separate good
> > and bad mutations. Some unlucky offspring get saddled with lots of
> > nasty mutations and die out, while the lucky ones get hardly any.
>
> > In theory, a mutation catastrophe can also occur as a result of
> > linkage. This refers to gene variants that are inherited together
> > because they sit next to each other on a chromosome. Suppose a
> > mutation that greatly increases the mutation rate somehow ends up next
> > to a new mutation that greatly increases fitness. The immediate
> > fitness benefits of the beneficial mutation will initially mask the
> > deleterious effects of the "mutator" mutation, meaning both mutations
> > will rapidly sweep through a population, ultimately with disastrous
> > consequences.
>
> > A few doctors hope to exploit mutation accumulation to treat diseases.
> > Certain viruses such as HIV are already close to the error catastrophe
> > threshold. Drugs that increase the mutation rate of the viruses still
> > further might push them over the threshold and drive a population of
> > viruses inside a person's body to extinction.
>
> > Finallly, it has long been recognised that the competition between
> > members of the same species to reproduce - sexual selection - can
> > favour traits that reduce a species' overall fitness. Male peacocks
> > with the biggest and brightest tails might get the females' attention,
> > but lugging around a heavy, conspicuous tail reduces their chances of
> > survival.
>
> > Studies of threatened bird species suggest that sexual selection can
> > indeed drive populations to extinction. Some biologists go so far as
> > to blame sexual selection for the conspicuous consumption that
> > threatens humanity's future.
>
> > According to the handicap principle, features such as peacocks' tails
> > evolve precisely because they are disadvantageous. Consider an
> > individual who is trying to signal to females how fit and strong he
> > is. If the signal is easy to make, weaker males can easily cheat by
> > making the same signal. But if making the signal is costly - such as
> > growing a large, clumsy tail or giving away food - there's no way to
> > cheat.
>
> > Proving that any of these phenomena have ever led to extinctions in
> > the wild is far from easy, because any species to which this has
> > happened are, of course, no longer around to study. The indirect
> > evidence is growing ever stronger, though.
>
> > The above is from this week's New Scientist. I've come across about
> > 20 misconceptions of evolution reading literature recently and, of
> > course, creationist myths are legion. My interest is indirect - I'm
> > looking for examples of why our debates are so little evidence based
> > for a theory of language.
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