From: Charles Hixson (charleshixsn@earthlink.net)
Date: Tue Apr 15 2003 - 08:28:56 MDT
Ramez Naam wrote:
>I've resisted weighing in on this thread, but I think there are a
>couple important point to make about human adaptation to the paleo
>diet.
>
>1) Paleolithic humans had a life expectancy of around 18 years. Just
>because they were adapted to a certain diet doesn't mean that it's the
>healthiest diet for those who want to live much longer lifespans.
>
It's important to note that this is an estimated mean life expectancy.
Infant mortality would have accounted for a lot of that. There's no
evidence that the maximal lifespan has gotten any longer.
>
>2) Related to point 1: Evolution selects for traits that maximized
>survival to reproduction, total lifetime fertility, and little else.
>Selection ceases after last age of reproduction. Selection is
>progressively weaker as less of the population is alive. Since we
>believe that only about 10 - 15% of the paleolithic population made it
>to age 40, and few of those survivors were reproducing, evolutionary
>theory tells us very little about what's healthy for humans past that
>age.
>
Evolution is a lot less perfect, and more inclusive than your first
approximation. The memory of the tribe, i.e. the elders, was a very
important element in survival. This is true even for animals that don't
have language. With the introduction of language it becomes even more
true. The elders remember that sometimes winters are difficult to live
through, so just because it's been easy for the last few years doesn't
mean you shouldn't prepare. That when you are crossing this dessert,
there is usually a spring behind that hill, etc.
>
>3) Humans are adapted to an environment with no antibiotics, no basic
>sanitation, minimal artificial heating and cooling, etc... However,
>each of those innovations has dramatically increases life expectancy.
>
Humans are also adapted to an environment involving living in small
groups in an area where one encounters those outside the local family
group (tribe) rarely. And to a basically nomadic lifestyle (well,
roaming over their territory in a path that took most of a year to
complete). In such a lifestyle antibiotics and sanitation aren't as
useful as they might be thought. Clothing, itself, is an artificial
heating and cooling mechanism, and it seems to have been one of the
earlier inventions (skin capes, at least).
>
>So basically I don't see much value in pointing out that we're
>evolutionarily adapted to a particular diet. That might mean
>something or it might not. I put more faith in large scale studies in
>a more modern environment.
>
The value is limited largely because we are so recently evolved as a
species. Our very dentition, however, is shaped by prepared foods. (It
allows teeth to be smaller and more delicate.) It's not clear that the
chemical adaptations have proceeded at the same speed. Perhaps we would
be better off living on a diet of fruit, bugs, and occasional mice,
squirrels, or gophers. But I doubt it. Still, there's much to be said
for avoiding MacDonald's.
>Those studies indicate that regular cardiovascular exercise, moderate
>caloric consumption, low consumption of refined sugar, low consumption
>of saturated and oxidized fats, and high consumption of fruits,
>vegetables, and whole grains are all associated with higher life
>expectancy.
>
>mez
>
Sounds both reasonable and unpleasant. (The exercise, mainly... the
rest, except for "moderate caloric consumption", I already do.)
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