For my 1000th post, a musing on natural selection

[Geoff R. Casavant]

I apologize for any racial undertones, they are not intended and not meant in any perjorative sense.

I think natural selection may have some very ironic jokes to play on us within the next hundred years.

It goes back to when slaves were transported overseas from Africa -- obviously, not given the best to eat or drink, many of them died. Now, among each boatload of slaves, there would be genetic variations, such that some would be more able to withstand this deprivation by a predisposition to retain fluids and salts. Those with this predisposition would be more likely to survive the voyage, and later passed this trait on to their children. This is one reason why high blood pressure is today more prevalent in the African-American community: now that food is more readily available, and higher in sodium, this genetic trait works as a disadvantage.

But, what happens years from now, when clean water becomes more rare every year? Then, the ability to retain salt and water could mean the difference between life and death. African Americans will be better equipped to survive.

Ah, irony . . .

Edited to correct some sloppy argument.

[SnoopDog]

1. Not being a doctor, I don't think this correlation holds water...

Pun unattended but how funny..?

Would three or four months on a ship warrant the genetic change as you suggest?

As I said, not being a doctor, maybe something else is more likley...

[Geoff R. Casavant]

3. No, the voyage didn't cause the change

It was the catalyst that applied selection pressure on a pre-existing genetic variation.

[SnoopDog]

6. Well, once again...

3 or 4 months, although lengthly, may or may not have provided the catalyst as you stated.

For instance, scurvy was prevalent amongst sailors as well, but I do not think genetic mutations permeated forward to their offspring....

[Geoff R. Casavant]

9. Well, how would we know?

Since it's been a while since scurvy hit the news, there haven't been many studies showing if different populations have greater resistance to the effects of Vitamin C deprivation. Or at least, none of which I am aware.

[madeline_con]

12. That's not long enough to affect change in a population.

[madeline_con]

2. HBP is linked to eating habits, among other factors.

Socioeconomic fact is, poor people tend to eat diets higher in fats and sugar because cheaper foods are cheaper in nutrients.

It's been af ew generations since the majority of AAs' arrival here, but not long enough for Darwinian sea changes.

[Geoff R. Casavant]

4. Please read my response #3

The genetic variation was always there, the voyage only provided the selection pressure.

[MercutioATC]

5. How does a voyage with bad food translate to a "genetic predisposition"?

I think I understand your contention, but it's really silly, in a "it changed their genes" sense.

(on edit)

I read your clarifications and (IMO) it's still silly. There simply wasn't enough external pressure to change the genetic preponderances of an entire group of people.

[Geoff R. Casavant]

7. Please read my post #3

The voyage did not cause the genetic variation, it only applied the selection pressure.

You're the third person in a row to mention this, I think I need to edit the OP to clarify.

[MercutioATC]

8. I edited my reply...I still don't think your premise is sound.

It's interesting. I've never seen it before. I'm personally glad I was exposed to it and had the opportunity to consider it.

I still don't see the influence as strong enough to have any significant impact on the genetic traits of the group in question.

(just my opinion...I have absolutely no technical credentials pertaining to genetics)

[Geoff R. Casavant]

10. I have no special expertise myself

In fact, the first premise of my argument, the part everyone seems to have the biggest problem with, I can't even take credit for. I first heard it on NPR, on a small show called Engines of Our Ingenuity(sp?); I don't know if your local NPR station syndicates it. I simply took it as a given.

[MercutioATC]

11. As I said, it's interesting.

Whether I ultimately agree with the contention or not, it's a good question to ask.

[bemildred]

13. Interesting, but probably not.

1.) OTOH, it's a rigid filter with no backmixing with the original population. To some degree it would depend on the death rate in transit and as a result of transit, which was fairly high I'm told, but high enough?

2.) OTOH the current population called "black" these days has been thoroughly mixed with both indigenous and other immigrant populations of all sorts, and in many respects it is more of a cultural than a genetic designation. In other words, the connection of modern day populations to the slaves fresh off the boat is, genetically speaking, tenuous.

I vote for crappy modern food.

[Odin2005]

14. I'm not sure about HBP...

...But I read that your risk of heart disease depends on the diet of your ancestors. Populations that have traditionally consumed a significant amount of meat, such as northern Eurpeans, tend to be genetically more resistant to bad affects of saturated fat and cholesterol and so have a lower risk of heart disease than populations that have traditionally ate meat only rarely, such as west Africans and thier African-American relatives.

[Igel]

15. I don't know that I believe the correlation holds water,

but I've seen it claimed before. The observation is that the prevalence of genetically-related hypertension in American AA communities is higher than the source population in Africa, and something must have driven it.

You need a certain level of sodium and electrolytes; during the Middle Passage those prone to sweat out minerals would die, since they weren't treated very well, and salt was valuable; this leaves those that tend to retain said minerals. In short order you tend to screen out those who don't retain electrolytes.

The counter claim is that field work under slavery forced the drift. Hot sun, long hours, poor food. You wind up at about the same place, but then there should be differences in the AA population/sodium-sensitivity by geography, and the descendants of both African and European/Slavic slaves in N. Africa and the Middle East should show a similar kind of drift.

In a sense, a similar claim's been made for indigenous Sonorans and diabetes. They have a much higher incidence of diabetes than Europeans, even controlling for diet. Their population has always had a starch-poor diet, unlike Europeans who've been exposed to high starch diets since the agricultural revolution took hold what, 10k years ago? The presupposition is that Europeans had a great wave of diabetes thousands of years ago.

In any event, AAs don't retain water: they tend to retain sodium. If they didn't sweat like everybody else, they'd need to survive at higher body temperatures, and *that* would be a feat. (On the other hand, it may be that whites over-sweat given raised temps. Dunno.) If the water AAs drink has a higher level of sodium than current potable water does, this would be a bad thing and lead to increased hypertension.