Just spitballing here, but can someone more scientifically inclined than I am (i.e., everyone) please tell me about any controlled studies of inheritable characteristics in humans that would support Darwinian theories of evolution, even on a provisional scale?
For example, I was thinking that we might have available documentation of very tall couples and the heights of their offspring who in turn married very tall spouses and so on for several generations, each of which was slightly taller than their parents were. And there might be similar documentation of mismatched couples, one being very tall but the other being short, and the resulting heights of their offspring, which when these studies were coupled together would produce evidence supporting a trend in inherited characteristics.
Have any such studies been done, and do they show what I’m (quite possibly ignorantly) speculating they would show?
I’m not really sure what you’re after. There’s the sickle cell gene, which is can be deadly if you have two of them, but can provide protection from malaria if you have one, and is found in populations where there has been malaria risk.
Northern populations tend to have lighter skin than southern populations, likely because of less sun exposure leading to issues with vitamin D in darker skinned people.
Europeans, who have used cows milk for longer than other populations, tend to be less lactose intolerant.
I think that Inuits and other populations that live in extremely cold weather have some adaptations that make it possible to thrive there.
Tall people having tall children doesn’t seem especially Darwinian to me – more just basic genetics. There are lots of studies about gene inheritance (eye color is the one we all learned about in school). Male pattern baldness and hemophilia usually come down the mother’s line because those genes are on the X chromosome (the Y chromosome doesn’t really have any thing on it).
I’m supposing practical, not theoretical, studies have been performed with human, not animal nor floral, subjects over a few generations that show certain strong trends in inheritable characteristics. I imagine these studies would educate people curious about evolution, if those who required such evidence were actually open to examining that evidence, so I’m wondering what the clearest cases of such studies are. It could be anything–height, eye color, IQ scores–I’m just wondering which of these are available for my perusal.
It’s complicated, because environment also plays a part (especially in height) and it’s not like you’re going to do an experiment where you take a hundred humans and control their diet from birth until death.
Well, take height. Assuming only the recorded heights, and laying aside other complicating factors, are there studies of a sizable number of subjects that demonstrate the sorts of effects I’m wondering about?
Seems to me if very tall couples tend to produce even taller offspring, then the other factors are a mere complication. That is, better nutrition can be accounted for by comparing these offspring to the general population.
What sort of thing are you wondering about? Do tall people tend to have tall children? The answer is yes, and I posted an article to that effect. It’s right in the summary – inherited gene variants play a large role in determining height.
It’s not 100% – some exceptionally tall couples may have kids that are shorter than them. I’m sure it’s a combination of genes that determine height, from both parents, and their interplay is complicated. And, that’s leaving aside environmental and uterine development, which also likely play a large role in height.
How do you do this? Raise hundreds of genetically similar children in various nutritional environments? Inject pregnant mothers with various hormones to see if any have an effect on height?
We’re doing some natural experiments with height and nutrition, unfortunately – I think North Koreans, who are genetically similar to South Koreans, tend to be a lot smaller due to their lack of food.
Sorry if I’m not being clear here – it’s not at all obvious to me what you’re asking about.
I’m sort of wondering why you seem to be emphasizing height. Is this of special interest to you?
Height is complicated as there are multiple genes that affect it, as well an environmental factors like food availability and general nutrition. Also, ever-increasing height is not actually advantageous. Although height can have its advantages, past a certain point increased height starts to decrease longevity and health. There’s an association between being tall and an increased risk of some types of cancer (this holds true for large breeds of dogs as well, and probably plenty of other critters as well). Past a certain point the very tall are more likely to have cardiovascular problems and early deaths, although that overlaps with pathological extreme height conditions, as opposed to people who just have a lot of genes for height.
Taller/larger people also require more food. While this is not a problem in our current world of abundance where a major problem is people eating too much, in the past when just getting adequate calories to sustain a body was sometimes a major problem being bigger wasn’t always a good thing. Especially in harsh/marginal environments.
It’s hard to do studies on people both because of the length of human generations and sticky ethical questions around human studies. However, a study of human populations does reveal some interesting things, some already mentioned.
In addition there is also the thalessemia gene, found in some Mediterranean populations with similar effects.
An exception are various arctic peoples who tend to still have darker skin than, say, Scandinavians, but those are also populations who have very high vitamin D levels in their diet, so there would, presumably, not be as much pressure for them lose skin pigment. There are also correlations with skin color and folate levels as well, but it’s the inverse, with darker skin being protective of folate and paler skin not so much.
On top of that, there’s the issue of clothing. There’s evidence that Neanderthals had some sort of clothing, apparently, which means clothing of some sort predates H. sapiens at least in some parts of the world. Clothing complicates the whole “skin color protects you from excessive sun exposure” thing, which is why you can find some people in sunny locations who have paler skins than their neighbors, who might wear less clothing. Human cultural practices influence our genes (that’s why some populations can still digest diary as adults) and we’ve had cultural practices long enough for that to have had a significant impact on our species.
There are are also African pastoralists with a different but also effective trait that also allows digestion of lactose in adulthood. The Masai are probably the best known and studied, but lactose tolerance in adulthood is not solely a European trait.
Maybe… but if so, they’re subtle. More a tendency to be stocky (whereas human populations that have spent generations in the tropics tend to be lanky). There might be some influence on circulation in the extremities and face but the evidence for such is extremely weak, especially as other ethnicities have capacity to adapt to colder weather as a general human trait.
There is, however, some significant evidence that Tibetans have high-altitude adaptive traits in their genetics not shared by other people, even others who live at high altitude. This makes them far less prone to altitude sickness, especially in the extreme HAPE and HACE forms that can be lethal. See here for a bit more information.
Don’t forget the epigentics - the conditions your grandparents experienced may express itself down the generations as well. Gene expression is not a simple matter of inheriting them from your parents or not. Research is still ongoing but at a minimum there are no clear-cut answers
Just an example of something that seems easily documented and pretty apparent to someone unacquainted with the subtleties of genetic research.
So far, I’ve been seeing some studies that seem to be giving me the sort of thing I’m looking for. Sorry if I haven’t been very specific about what exactly I’m looking for–it’s not entirely clear to me. But this has been helpful–thanks.
Humans are a poor choice for breeding experiments because of their very long generation time- ~20 to 30 years. There’s also the problem that only a superhuman agency could impose the rigorous conditions necessary for an experiment to be valid.
There is also the case that apparently Indigenous inhabitants of the higher areas Andes have some adaptions (especially lungs) for breathng thinner air, although I’ve not read about any matching adaption for Tibetans.
To pick the example of height - there’s not some magical gene combination that consitently gives 10-foot humans, only wating to be collected in one individual. There’s not even the guarantee that abnormal height is totally a genetic thing - overproduction of growth hormones could be a singular developmental accident. similarly, there was another thread discussing why we have wildly different shapes/sizes of dogs but not cats - is there any indication human genes are as flexible? Based on the general lack of human shape variation - we are cat people.
The process described - keep breeding the most successful with those attributes - that’s how humans breed assorted domestic animals. They are however better isolated from outside evolutionary pressures. (One item I heard about modern over-bred domestic animals is that by concentrating on things like size or milk production, we’ve bred out a lot of the survival intelligence that normal animals have,
For humans - there’s the square-cube law. 50% bigger is more than three times as heavy, but only twice the bone cross-section. With evolution, with time, upscaling selects not only for size but for the robustness to handle that size;elephant legs are stouter than horse legs, which are stouter again (proportioante to size) versus mouse legs. Whoever bred Clydsdales seems to have figured this out, whereas it seems racehorses regularly have leg bone problems. But in general, Mother Nature (i.e. evolution) has settled on “just right”. Messing with that balance is not simple. The two most extremely separated groups by time, IMHO would perhaps be between inhabitants of Tierra del Fuego and Australia (40,000-plus years?), and the differences there are still minimal.
I suppose the biggest problem with any experiments is the time it would take. Staying on purpose for dozens of generations is unlikely.
But they are invariably what evolution-deniers or ignoramuses want to hear about, so that started me wondering about best-case studies to show them, flawed or incomplete though they might be (the case-studies, not the ignoramuses, though they are too.)
There is no such thing as evidence which will speak to an evidence-denier. It’s the old saw: you can’t reason someone out of a position they didn’t reason themselves into. So you’ll never find a case conclusive and definitive enough to satisfy a denier.
Twin studies may come as close as you’re going to get. Identical twins raised apart, fraternal twins raised together, etc. They are all a kind of natural experiment:
I suspect you don’t understand the deniers’ delusions well enough to refute them. In general, creationists and other deniers of evolution don’t deny microevolution (changes within species); they deny macroevolution (evolution of new species). Cite from a nutjob creationist website.
Finding examples of microevolution within a species like humanity won’t do anything to satisfy their doubts about macroevolution.
Yes, both my parents are tall, as are my three siblings. I started out as barely clinging to the bottom of the average height range, but I’m now unequivocally short. My sibs said I was a “throw-back” to our 5’7" maternal grandfather. Grandmother was taller than he was.
Although the indigenous people of the Andes do (apparently) have some adaptions to high altitude living a number of them are different adaptations from the Tibetans.
The Tibetans not only have different adaptions, they are even better adapted to high altitude living than people from the Andes (the next highest group of people). This may be because people - of one sort of species of the genus Homo or another - have been living on the Tibetan plateau longer than they have been living in the Andes mountains. Prior varieties of humans, such as Denisovans, may have passed on genes that were of use to adapting to the altitude. One sign that the Tibetans are different than the rest of us (including indigenous people in the Andes) is that Tibetan women can sustain a pregnancy at higher altitudes than women of other ethnicities, their babies are less likely to be underweight after high-altitude pregnancies, and their children grow faster at higher altitudes. And that includes when they are compared to indigenous people of the Andes. Are these huge differences? No. But there are statistically significant and notable differences.
This makes some sense. Early H. sapiens migrating to the Tibetan plateau may well have intermarried (or at least interbred, unfortunately these things aren’t always voluntary) with earlier varieties of humans already living there, conferring some helpful traits on their descendants. Meanwhile, the people who would one day settle in the Andes were standard sea-level H. sapiens who made the long trek there, where there weren’t prior humans living, and had to re-evolve high-altitude traits out of whatever random changes time gave them. Thus, we have an example of convergent evolution in two separate human populations.
It probably only took about 10,000 or more years for that to happen. Which is why getting solid evidence for this sort of “just so” story is so very difficult.
Be careful. One of the most cited twin studies, identical twins separated at birth, was to demonstrate that intelligence was hereditary. As one later critic discovered, “how did this guy find so many identical twins conveniently separated at birth and raised in diverse environments?” Apparently making up shit to “prove” that intelligence was mainly hereditary was a critical step. The study was accepted and cited for so long that it’s findings are often quoted second or third hand and embedded in the literature even though the original was discredited.
The most obvious natural selection is the disappearance of melatonin to some degree in populations from less sunny environments. This process appears to have taken millennia.
Another fun fact I’ve read is that male-to-female size depends on whether the society is polygamous or monogamous over the centuries. When less food resources are available to women, the smaller tend to survive better. Not sure how true this is.