Re: lack of evolutionary pressures

[Adam Back <aba@dcs.ex.ac.uk>]

Tim May <tcmay@got.net> writes:
> Main point: The human genome is now "weighed down" with more than 7
> billion persons, a large fraction of them still capable of
> reproducing. Bluntly put, it ain't going _anywhere_, at least not
> very fast. Changes in the characteristics of a species, loosely
> speaking, "evolution," happen faster in small populations.

I can see sufficiently small populations evolving quickly because in a
small population -- say 10 monkeys -- the monkey which got run over by
a truck because it was deaf, splat, end of deaf monkey gene, if it's
the only one.

But over large numbers say 700,000 or whatever, I can't see that it
makes much difference whether it's 700,000 or 7 billion.

I would've thought at that point it's more to do with the proportion
of the population with the genetic feature in question and the
magnititude of evolutionary pressure exerted by that feature.  

Clearly environment affects this, and a large population is more
likely to be geographically dispersed, and hence less prone to sudden
adverse environmental changes.

> The tribe of hominids forced out of trees by loss of forestation in
> the Rift Zone, for example, will undergo rapid changes over a few
> hundred generations.

So if 10% of the hominids by chance have an genetic characteristic
which increases their chances of `hacking it' long enough to propogate
their genes with no trees to 90% as compared to 20% for those without
this characteristic, clearly that gene set is going to propogate
pretty damn fast.

You could get some pretty fast propogation even in a population of 7
billion.  If there were an AIDs like virus with a airborne common cold
propogation vector, and a year incubation period, and 1% of the
population had some quirky genes which just happened to make them
immune to it, well that 1% gene would propogate very quickly.

> Billions of humans in the modern era, with essentially everyone
> reaching reproductive age, will not. The human genome is like a
> supertanker being hit by tennis balls: it just won't move.

There are currently practically no physical genetic advantages which
radically affect ability to breed (apart from extreme ones which mean
near certain death).  So yes, it's stagnant from that point of view.

There are however significant pressures exerted by different cultures,
which have different genetics.  Some cultures shun the idea of birth
control, and tend to have 2 or 3 times more children than average
educated westerners.  If that statistic holds for a few generations
there will be a lot more people around from these cultures.  There are
I think enough genetic differences between european genes and arabs,
asians as an example that I think it would be reasonable to argue that
this is having an effect on the human gene pool.

It is our collective shared memes which are suffering large scale
negative evolutionary pressures.  Be socially responsible, global
warming, food shortages, have few children.  Lots of other reasons
people don't have so many children ... gets in the way of career, long
term chore, commitment etc.  Reasons for welfare recipients to breed
more welfare recipients.

> Dumb people tend to mate with other dumb people, more or less. Lots
> of reasons for this, but look around and confirm it. So, this will
> lead to an ever-broader Bell curve of intelligence, right? Nope. For
> whatever complicated reasons, the curve has essentially reached its
> "normal broadness," to invent a phrase.  Or so I think is the
> case. Certainly there are ample statistics to show this.

That's a pretty interesting result.

Intelligence is an awfully hard thing to measure.  IQ tests and SAT
scores only show you what they test, ability to score at IQ test and
SATs.

> If Adam likes children, or wants them around him for whatever
> reason, fine. But any notion that 2 or 3 or even 5 children will
> affect the genome is wishful thinking. Look at the math.

A change in cultural values, societal norms, and welfare structures
over a sustained period could start to have some effects.

(Cultural norms change -- one of my grandfathers, an englishman, was
one of 20 children -- this used to be much more common.  17 of them
made it to adult life).

> (And not even the infamous "But what if _all_ smart and educated
> people thought this way?" applies. First, what Adam or Tim or Blanc
> does about having children will not affect the decisions of
> others. Magical Thinking 101 again.

Memes propogate in meme-space also.  The meme of global warming,
potential food shortages

> >The problem is that from a purely scientific evolutionary point of
> >view, the human race is surely regressing, the masses of negative
> >evolutionary pressures are certainly pushing this way.
> 
> I doubt this in the strongest possible way.
> 
> Australia was populated by the common criminals of England, the
> louts and scoundrels and thieves and murderers. (Perhaps some
> "political prisoners," but mostly common criminals.) And yet within
> a generation or two, Australia was thriving, and today nobody would
> argue that the descendants of convicts are dumb or backward.

Likely due be a number of effects, perhaps demonstrates that
intelligence and being exported from England don't necessarily
negatively correlate.  Also perhaps intelligence isn't that strongly
based on genetics.

There probably weren't any significant average genetic differences
between the freshly exported "scoundrels" by 18th century standards as
compared to the average genetic make up of english population.

Also I did hear that Hitlers super-race of children bred for selected
traits didn't work out that well.  Perhaps the environment they were
bought up in didn't help.  

Are there any studies which demonstrate any difference in intelligence
between races even, asians, africans, chinese, europeans, red-indians
etc?

There seems to be an observable difference in business acumen between
races .. of course this could easily be explained by their society and
customs.

Adam
-- 
Have *you* exported RSA today? --> http://www.dcs.ex.ac.uk/~aba/rsa/

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