Man I like this site…but I’m always reading these past posts and coming up with questions to questions that are almost 20 years old! This question was from Mar. 23, 1984 http://www.straightdope.com/classics/a1_098.html .
It reminds me of a sci-fi book I read a few years back, wherein all of humanity was homoginized and a whole lot of individuality and creativity was lost as a species. C. used Brazil as an example…but it doesn’t really apply to the whole of humanity does it? He cites a declining African influence with a steady European influence…it’d be like adding more cream to the coffee in the same cup. The question was for humanity as a whole. Ie: What’s a good
guess at human adaptation rates to climate influences (in years or generations) vs. the “civilization” of the world…changing the environment instead of adapting. (Interesting that a couple of topics ahead in the archives talked about Eskimos being adapted to living in the cold…how long would it take to make a Hawaii Eskimo?) Also that whole Milk: A European drink etc. argument…how many generations would it take of African American school children drinking milk on a daily basis to generate the lactose tolerant gene?
Or would it even factor in…? Does exposure affect mutation, or is it natural selection? (Can’t see how drinking/not drinking milk would lead to a increased mortality rate in modern America.) As poor eyesight is no longer a survival weakness (due to glasses, surgery, farming, etc.) are our eyes getting weaker? (I see alot more people wearing glasses now than when I was a kid.)
Not that it’ll affect me personally…I’ll be long dead (maybe) before all this become apparent, but it makes me wonder if we shouldn’t be learning more about our own DNA…survival is usually a matter of adaptation, what happens when we, as a whole, stop?
Um, welcome?
I think you’re right about Brazil not being a good representation for the world as a whole, since the population influx of whites over blacks affects the outcome. Given population rates, right now a good guess is we’ll all end up Indian (India’s population is chasing China, but China instituted draconian population control and India hasn’t.)
As far as the African children drinking milk to develope the lactose tolerant gene, it doesn’t work that way. Mutations don’t typically respond to exposure. Besides, adult milk use is not really a strong factor in survival rates, so there’s no selection pressure to increase the survival rate of lactose tolerants over intolerants.
Conceivably the same thing applies to eyesight, and as a whole our genetics on eyesight are weakening. Of course, it could just be due to more reading and watching television driving more people to spend long periods of time focused close. You are correct that the more we learn about genetics, the better our ability to affect lasting cures that mean our children won’t have our weaknesses.
I don’t think you have to worry about us stopping adapting. That’s not possible. However, we as a species have got a strong track record of adapting our environment to suit our needs (vs. the other way around). Some people could be overly worried that we get too used to it and then some change we can’t control appears and slaps us hard. Perhaps global warming, perhaps loss of rainforests, perhaps less diversity of ecosystem, or just pollution. The result is new pressures on our adaptation. Some people look forward to the bright, shiny future of fully synthetic bodies that we don’t have to worry about so much. Others dread that possibility as a nightmare.
I can’t respond to the rest.
Actually, adult milk use is exactly the kind of use pointed to as important in survival rates and selection pressure.
More specifically, the connection is that people who manufacture lactase as an adult to digest lactose also appear to digest calcium more efficiently. They may have stronger bones as a consequence. Women might survive labor better and produce more and healthier babies. Men with stronger bones and healthier bodies may live longer and sire more children (or be more attractive as mates). Since the mutation that allows adult lactose tolerance is a dominant one, these children are likely also to be tolerant to lactose as adults and continue to spread the gene through the population.
A very common misconception about dominant genes. The fact is, if two parents expressing a recessive trait have kids, then all of their kids are guaranteed to express that trait as well. But people who express a dominant trait can have a recessive gene hiding in the background, so it’s perfectly possible for two people who show a dominant trait to have a kid who shows the recessive trait.
To make this more concrete: RH+ is a dominant trait, and RH- is a recessive trait. If both parents are RH-, their children are alll guaranteed to also be RH-, and if they mate with other RH- folks, their children will be, as well. But two people with RH+ might each be also carrying an RH- gene, in which case their children have a 1 in 4 chance of being RH-, and a 3 in 4 chance of carrying the RH- gene.
Note that I said “likely.” I define three out of four to be likely.
Your example is correct in numbers but exactly backward in application.
Let’s look at your case. Say that RH+ is adult tolerance of lactose; RH- is lactose intolerance after weaning.
Parent A: RH+ RH-
Parent B: RH+ RH-
Possible children:
RH+ RH+
RH+ RH-
RH- RH+
RH- RH-
Your are correct that three of the four children will have RH-. But the important point is that three of them have RH+. If RH+ is dominant then in three of these cases, the children will be adult tolerants of lactose.
Look at this case, with only one parent tolerant:
Parent A: RH+ RH-
Parent B: RH- RH-
Possible children:
RH+ RH-
RH- RH-
RH- RH+
RH- RH-
Even with only one gene present, half the children will be tolerant.
And this case:
Parent A: RH+ RH+
Parent B: RH- RH-
Possible children:
RH+ RH-
RH+ RH-
RH- RH+
RH- RH+
Voila! All children will be adult tolerants.
Of course, this is not of much use unless the tolerance provides other benefits as well. It does, which is why northern Europeans and their descendends are as much as 97% adult tolerants.
Right, but you also said “continue to spread the gene through the population”. A person can spread a gene regardless of whether they express it or not. In fact, in cases where the less-advantageous gene is recessive (I’m assuming here that lactose intolerance is less advantageous), the advantageous gene will take longer to take hold, since you can still have recessive genes lurking around in dominant-trait carriers, just waiting to be matched up.
If I can sum up:
My point is that an advantageous dominant gene will quickly spread through a population.
Your point is that a recessive gene can stay in the population, even if disadvantageous.
Both are true, inverse sides of the same population genetics.
However, what Irishman said was just plain wrong, and that’s what I was repying to.
Do we still need to argue this?
<< My point is that an advantageous dominant gene will quickly spread through a population. >>
By “quickly”, of course, you mean in a few hundred or thousand generations…?
Archaeologists can’t give an exact time for the peoples who reached northern Europe, but it can’t be more than 7,000 years ago. They certainly had a dairy-based culture at least a thousand years ago. At an extreme, therefore, the changeover was made in 6000 years. At 25 years a generation, that’s 240 generations maximum. The true figure is probably less than 200 generations.
In population genetics I would certainly call that quickly. Do you disagree?
Yes. A sort of dusty-brown color.
When? About 1-2 years after their death & burial. (Though Shakespeare says it will take a bit longer for a tanner.)
For those whose religion leans toward cremation, it will be more grayish dust, and will occur rather sooner.
According to Bulworth, yes.
“All we need is a voluntary, free-spirited, open-ended program of procreative racial deconstruction. Everybody just gotta keep fuckin’ everybody 'til they’re all the same color.”
we already are pretty much the same color: somewhere around 10,000 nm. Now the question is whther we will ever be able to see ourselves in that light (no pun intended).
If current trends continue (i.e. barring a technological collapse or the establishment of racial homelands), all people will be “the same color” at some point in the relatively near future, probably the next 1000-2000 years. If current birthrates and migration patterns continue, that color will likely be on the darker side of the now-existing spectrum of skin colors.
Is that a good thing or a bad thing? Hmmm, there’s the controversy. My opinion is that it would be a sad loss for future generations. I am always a little amazed by people who talk about the value of racial diversity one minute and then about the glorious mono-racial future in the next.
My experience in Latin America, including Brazil, is that while there is a lot of mixture - there are still very real racial divisions - often in ways where there are none in the United States.
For instance, what most Americans would call “blacks” are divded between those who are dark and have mostly African ancestry, those that are about half and half, and those with mostly European genes. So where we have one “Race”, in Brazilian society there are three or more.
syncrolecyne, the U.S. “one race” that you speak of was not always the case here, historically. It is an outcome of the equal rights movement in the '60s. As part of the Black pride movement, previous distinctions of the types of Blacks were obliterated. Before then, we were happily applying terms to the various degrees of white vs black, just like Brazil does now.
I think we may be a little short-sighted when saying that eventually we will all be one color. We are assuming a continuation of the present migration patterns etc. but are forgetting the effect of future technologies on the question. With genetic engineering gradually gaining acceptance, inevitably the cost/benefit ratio will allow just about ,if not everyone, to create whatever colored kid they want. While cultural constraints will probably limit the number of neon green kids, we’ll probably continue to see a variety of skin tones from shimmering samite to blue-black. Good thing too, it’d be sad to loose the beauty that comes with diversity
Properly educated, we can all remain our happy selves. Good enough for me. -Rod-