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| Richard Dawkins: old age is the price we pay for our “gilded” youth |
Everything about mankind has been shaped by Darwinian natural
selection and this applies equally to bacteria, viruses, cancers and diseases,
said Professor RICHARD DAWKINS (professor of the public understanding of science,
University of Oxford) on September 13.
Speaking about the effects of evolution and natural selection on physiology,
disease and ageing, Professor Dawkins said that natural selection was both powerful
and fast. Humans had experimented with selection and, for example, had created
the dog from wolves in just a few centuries.
Nature had done likewise in the wild and had achieved enormous changes in a
short time, especially in creatures with a short life span. Even with almost
undetectable selection in favour of larger size, it would only take 12,000 generations
for a mouse-sized creature to become elephant-sized, he said. This was such
a short time geologically that it would appear to be instantaneous in the fossil
record. Thus, it should not have been a surprise when bacteria developed resistance
to antibiotics, it should have been expected, because 20 generations of bacteria
could pass in one day and great changes occurred rapidly as a result, he said.
Trade-offs
Professor Dawkins then moved on to the subject of evolutionary “trade-offs”.
It was possible to breed mice that were resistant to tooth decay, so why had
this not happened naturally? It was probable that being resistant to tooth decay
led to a penalty elsewhere in the body.
It was possible for the body or a system to be to be overdesigned but evolution
tended to achieve a balance, because natural selection designed for economy.
For example, if all bones in the body were subject to fracture except the fibula,
the calcium from the fibula would, over successive generations, be “robbed”
to strengthen other bones until all bones were as likely as each other to break.
Another example of economy was the mayfly, which in its adult reproductive form
had no functioning gut and only lived for one day. This was because resources
had been channelled away from unnecessary feeding equipment and towards organs
for flight and reproduction.
Professor Dawkins then posed another evolutionary question — what was the
advantage in growing old? What was the “survival value” in old age
and death? In theory, old individuals were no more likely to die than young
ones. (He illustrated this by saying that old test tubes were just as good as
new ones but at some stage all test tubes got broken.) Darwinians thought that
the explanation lay in the survival of genes. Every creature was the way it
was because of the genes it had inherited from its ancestors. Individuals died
at the age they did because they had come from a long line of ancestors who
had also died old. The older an individual became, the more likely it was to
pass on its genes before it died. Thus, genes that predisposed individuals to
a young death tended to be stopped, while those that gave longer life survived.
Which was most likely to be passed on — a gene that made the individual
fitter when young at the cost of making them less fit when old, or one that
had the opposite effect? Genes for beneficial effects tended to be expressed
early in life with a trade-off later, so old age was the price we paid for our
“gilded” youth. This was why men came off worse than women, in that
they tended to die earlier, he said. Men had to compete with other men when
young, so that it was better to have more advantages early in life, with the
trade-off of an earlier death. Women tended to have a more nurturing role and
lived longer. It was a case of either surviving “for the long haul or competing
for short-term success”, Professor Dawkins said.
Arms race
In nature, much of evolution was driven by an “arms race” between
predators and prey. Both predator and prey became better able to survive via
evolutionary processes driven by the need to keep improving. It was in the interest
of both to shift resources into the ability to run and to outwit their opponent.
However, other systems suffered as a result.
Survival of the fittest was not a struggle between species but within them.
It was more important for members of a prey species to be able to outrun each
other so that they were not the one caught than it was for them all to be able
to outrun the predator. The hare ran for its life but the fox was only running
for its dinner.
Parasites
The relationship between parasite and host was similar but more complex. Predators
were good at catching many sorts of prey but parasites were more specific and
generated specific counter-attacks from their host.
Many people thought that parasites became “kinder” to their hosts
in order to keep the host alive but this was not the case. The parasite was
not competing with the host; it was competing with others of its species in
one host. Therefore, it was in the interest of the parasite to be ruthless and
beat other parasites. However, the degree of ruthlessness depended on how the
parasite got into its next host. Again, there was a trade-off between survival
and the need to kill the host off quickly in order to move to the next one.
The cold virus only made its hosts slightly ill, he said. This was because the
virus depended on being sneezed on to someone else in order to move to a new
host. In contrast, malaria parasites were conveyed between hosts by an insect
and could afford to be less kind. There was no advantage to the parasite in
having a well host, as having a prostrate host made it easier for mosquitoes
to bite. Using mosquito nets would eventually induce the malaria parasite to
evolve into a kinder form, as it would become an advantage to have a reasonably
mobile host who could be bitten by mosquitoes rather than an immobile host who
was always under a net.
In the same way, use of condoms would gradually induce sexually transmitted
diseases to become more kind. If condoms were not used, it would be quick and
easy for diseases to move between many people, so there was no advantage in
keeping the host well. Condom use cut down the chance of the disease finding
a new host, so it was more important to keep the host alive and well for longer.
An example of “extremely kind” parasites would be chloroplasts and
mitochondria, which were so benign that it had only recently been discovered
that they had been parasites, he said.
Professor Dawkins recommended ‘Evolution and healing — The new science
of Darwinian medicine’ by Randolph Nesse and George Williams for pharmacists
who were interested in Darwinian medicine