Research into inherited characteristics?

This is called “gene \times environment interaction”, and can be difficult to deal with in something as simple as twin models. There are ways to test for it, such as adoption studies, and newer methods using measured genetics (a list of a whole bunch of SNPs, like what you get from 23andme). G \times E interactions are something that people studying genetics spend a lot of time thinking about.

Intelligence and education level are correlated, and studies will often use education level as a proxy for intelligence, because education level is extremely easy to get from a single question that may have been asked on a study about heard disease (for example), that didn’t ask anything else related to intelligence. However, it is important to remember that they are not the same thing. Things like SES and racism may play a greater role in educational attainment than in intelligence.

Education level is also heritable. Which, again, just means that some of the difference between people’s education level is due to differences in their genes. Doesn’t mean all of it. Doesn’t mean that future education level is somehow fixed at fertilization or gamete formation. Also doesn’t mean that group differences in gene frequency are responsible for group differences in education level. It does mean that we can come up with “risk scores” based on your genes to predict education level, but prediction \ne destiny.

My grandfather was nothing special, both my uncles were farmers, my father was a college professor who went throught university on scholarships - the point is that intelligence, whatever else, is also arbitrary and variable even in the hereditary component - which compunds the problem of trying to determine what is intelligence and how is it hereditary.

This is a fallacy of thinking about heritability wrong. Saying that the heritability of intelligence is 50% doesn’t mean that people can only be as smart as their parents were.

People have different levels of intelligence (or height, or risk of cardiovascular disease, or age of onset of Alzheimer’s, or whatever). Some of that difference can be explained by differences in genetics and some of it by differences in environment.

The ratio of genes to environment can also change across time and environments. A bit of a just-so story: in a society where all children get access to adequate nutrition, differences in adult height will be primarily due to differences in genetics; in a society where some children are malnourished, and others get adequate nutrition, then adult height will have a large environmental component.

A more statistical way to say that is: The variance of the phenotype is composed of the variance due to genes, and the variance due to environment.

V_P=V_G+V_E

Changing the variance of any of those variables will affect the other variables. If all kids eat well (low variance in environment), then the variance left in the phenotype (height) is going to be mainly due to the variance of genes. An opposite situation could be something like inbred strains of mice. There is no variance in genetics, they are all identical, so any differences in phenotype are going to be due to environment. (All of this is of course simplified, and there can be more additional complications, but that doesn’t change the fundamental points).

Bringing it around. Difficulty in defining intelligence is not due to the fact that it is something people have different levels of. If everybody had the same amount of it, then it would not be an interesting trait to measure.

So, you’re grandfather and uncles may or may not have had high intelligence scores. Being smart can certainly help somebody be a better farmer. However there is not a perfect link between intelligence and education level or intelligence and career. It is a positive correlation, and pretty high one at that, but a high positive correlation by definition leaves room for individual cases where the relationship between intelligence and career is low. Otherwise the correlation would be 1.

Similarly, you expect a person’s first degree relatives to have a similar intelligence score to that person, but not the same score. In some cases it might be quite far off. A group of first degree relatives having dissimilar scores doesn’t disprove heritability, it just shows that the variance is not entirely due to genetics.

This was not my point at all.

First, how the genes are expressed can itself be variable - not just because every human is a mix of genes from both parents - so presumably, at least 2 different genes, but likely many more, determine overall “intelligence”. Which particular cards of the deck a person recivesin their hand can be variable, and sometimes people are dealt a royal flush, but usually just 2 pair. Thsi does not even consider the issue of which genes express or not. (I’ve seen discussion of “mosaic” gene expression, suggesting this is why women -with 2 X instead of an X and Y - tend to be more toward the center of the distribution, while men tend to manifest more often as outliers. (of course, this may be unconscious bias or social pressure).

Second, even in the same household, conditions such as nutrition or attention may favour one over another. Did my father as first child benefit from more attention before his brothers became rivals for parents’ nurturing? (Are there papers on whether the older tends to be “smarter”?

Both V’s can be variable for any child of the family, so total predictability of apparent intelligence can vary… Although true, if the family has a preponderance of intelligence genes, then we would expect that in general the children will tend toward the higher side, and vice versa.

My point was that it is diffcult if not impossible to measure or separate the proportion of contribution by genes or environment to any serious precision other than to say “there are indications that…” Certainly not to the precision of 1 in 10 or 1 in 100. Without even compounding it with the question of what exactly is intelligence.

Yes, that is true. In this case though we’re not thinking about the expression of any single gene, but the aggregate expression of all genes.

Also completely true. This generally results in breaking up the variance due to environment into two parts: shared (or common) environment and un-shared (or unique) environment, which just to be supper confusing are often called V_C and V_E, These can be viewed completely mathematically where V_C are things that make siblings (or any two people for that matter) more similar, and V_E are things that make them less similar.

This is not true. There are many statistical techniques that can be used to measure the contribution of genes and environment (V_C and V_E) to any particular trait. Twin studies are just one of the techniques. It definitely can be difficult, but is not impossible. Of course it is going to be dependent on what you mean by “serious precision”. Is “about 80% of height is determined by genetics” good enough? If not, then you pretty much have to throw at all psychology and medicine. Yeah, we can’t say “exactly 78.23% of height is determined by genes”.

To be even more frustrating, saying that 80% of height is due to genetics does not tell us anything about which exact genes are responsible for that, and how they’re accomplishing it. That information will require different studies.

All of that is for things at population levels. Height can by 80% heritable, yet this one person from a tall family is short because of the chance affects of a childhood disease, or perhaps a novel mutation. Measured genetic techniques are bringing us closer to describing exactly what genes and parts of the chromosome influence any particular trait, but we’re not there yet.

This is also something which is difficult, but not impossible to define. There are many scholarly books and articles written on the subject. To me, in discussions like this one, it often seems that people don’t want to define it, because they don’t like that something like intelligence can be summarized with a single number. Yet, when those single numbers are collected on many people, they can tell us a lot about the relationship between intelligence and other things. People don’t come with kind of intrinsic D&D character sheet with a “true” intelligence stat, so of course the number isn’t perfect, but in these things “good enough” is often as good as we can do.

Yes, good enough is as good as we can do. That’s all I’m saying too.

(Maybe my uncles were fairly bright but lazy and non-competitive like me…)

Same here. My dad had two years of college, and my mom had none, but we were all (except my brother) big readers.

The talk is how the “survival of the people with the best medicine” is overriding “survival of the fitest”.

It would take many generations to find evolution… Its implausible.

epigenetics confounds the issue too. Something like height could be in epigenetics… For example that in times of famine or physical stress, the children may have epigenetic instruction to grow smaller … perhaps faster to study, but harder because its not in the genome sequence…

Survival of the fittest has to do with the environment the organism is in. If that environment includes medicine then it doesn’t stop evolution it changes what is now favorable. Those with a higher tolerance for medicine’s side effects and adverse events will do better than those without such tolerances.

Humans are also weird in that a significant number of people who do have genetic defeats will either opt not to reproduce at all, or these days, if they have the means, use medicine to make sure those genes are not passed on to the next generation.

Gray hair is an indication of reverse genetics. The condition is inherited from your kids.

Generally, this doesn’t apply to people living out longer “senior years” periods in modern times. Absent a game-changing mutation (vanishingly rare) … evolution is “bent” (ever so gradually) by things that influence likelihood/viability of reproductive success, which generally manifest in early adulthood.

IOW: from an evolutionary standpoint, a person with means to access medical resources that keeps them alive into their nineties is not “fitter” than someone who died of a heart attack in their 50s.

Lots of caveats and exceptions apply, but not enough to weaken the overall point – evolutionary fitness is about reproductive success, not about extended old age.

Though isn’t living into older age potentially an evolutionary advantage?

There’s the line of argument that having non-reproducing caregivers available to care for the young or to pass on skills or do productive, albeit less intense, work can free up younger adults and provide a reproductive advantage that way.

Yeah, that’s one of the caveats. How big a needle-mover that is evolutionarily, I’m not sure.

Perhaps there’s a sweet spot, age-wise: It’s evolutionarily helpful to have more spry 60- and 70-somethings around, but it’s evolutional neutral or negative to have individuals’ end-of-life infirmity period extended.

My thought would be that modern society would select against very old people. If your parents live into their 90’s or 100’s (speaking from experience) then the children will be less likely to inherit anything until they are pushing 70. Whereas those whose parents die early (60’s) with enjoy a stress-free parenthood with the money from their inheritance, and afford more children and a nice house, student loans paid off, instead of all that money being eaten up by medical costs and senior care homes.

Of course, this situation has only manifested itself in the last generation or two with modern medicine, so it will take a long while before resistance to modern medicine creates a difference in predominant genetic traits.

That is making the assumption that there is anything to inherit, or anything significant, even without the problem of medical costs. There are significant numbers of families where even relatively young parents have nothing to leave their descendants.

Meanwhile, if elderly grandparents can remain healthy (because not all elderly people are physical wrecks) they might provide more assistance via things like childcare than they would by leaving just a few dollars after passing away.

All this presupposes some kind of ‘optimal’ age.

Really, a few extra years (or even a decade or two) may not end up being enough to select against if there’s enough benefit to general longevity in the first place to offset some inefficiency on the other end.

Yes, but none of this is related to evolutionary fitness – to be blunt, fecundicity.

It depends whether those whose parents die early leave enough money (usually) to allow their offspring to afford a ifestyle that inclues more children - basically the opposite of the grandparent hypothesis.

The ones who last into their 90’s are less likely to have much assets left, especially with medical and senior living home expenses. The oness who die early unexpectedly leave retirement savings and possibly the family home to their offspring. OTOH, if the kids spend it instead on an exotic vacation and on birth control there is no evolutionary advantage.

(It’s also shown that once a family reaches a much higher level of richness, they tend to have more children than the average 2 or less.

That’s a good point - maximum lifespan might be a side effect of extending an earlier developmental stage. If an extended childhood provides survival benefits for humans than the changes permitting that might extend the overall lifespan. Likewise, changes that allow a longer “healthy adulthood” period to allow enough time to raise extended-childhood offspring might affect the length of old age.

For many people, their children are their retirement policy. If you don’t have any expectation of having funds to retire on - which is still a huge fraction of the world population - an expectation that you will need support into your old age is a very significant incentive to have children.

Correlation versus causation and all that, but IMHO there is good reason to think that drops in birth rates as modern societies become wealthier has a lot to do with this.