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I was rather surprised when I looked at these numbers. Our popula-
tion is so gigantic that even if we were all retrofi tted to be able to munch on
newspapers and cardboard boxes every day, followed perhaps by a paper-
back romance novel for dessert, we would still be faced with widespread
starvation unless we chopped down even more forests than we do now.
It would simply not pay us as an entire species to carry out these drastic
modifi cations. But this new lifestyle might appeal to those of us who would
like to move beyond a vegan diet to the ultimate in recycling. A swollen stom-
ach and infl ammable belches might become proud signs of a raised ecologi-
cal consciousness.
Evolution and its limits
As we contemplate the dii culty of feeding our growing population, we con-
front the same biological limit that gave Charles Darwin his fi rst clue to the
mechanism of natural selection. When he returned to England from the voy-
age of the Beagle , Darwin read a gloomy book by the clergyman T. R. Malthus,
called On Population . Malthus pointed out that our population increases geo-
metrically, while the resources on which we depend increase linearly if at all.
Darwin realized that Malthus' limits on available resources apply to every
species. His great insight was that as the resource limits are approached,
some members of the population will have a better chance of surviving than
others. It is this dif erential survival that results in natural selection.
Despite our recent population explosion we are not immune from these
Malthusian limits. We are now six times as numerous as we were when Dar-
win returned to England on the Beagle in 1835. Even drastic genetic engineer-
ing of our digestive systems, turning us all into methane-belching ferment-
ers, would not be enough to maintain our present and future numbers. We
may be able to postpone the inevitable for a little while, but it is clear that
we must either control our own population or have a much less forgiving
Mother Nature do it for us.
This chapter has given you a brief sketch of how evolution actually
takes place. We have seen how genetic variation, the tank of gas that powers
 
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