chazwomaq t1_jb23r2v wrote

>100 heritability implies variation in trait amongst a population is wholly accounted for by variation in genetics of population


>and there is no correlation between variation in environment causing additional variation in traits.

I would phrase it as "environmental variation does not cause additional variation in the trait".


chazwomaq t1_jb09sjt wrote

>The way I read that 100% heritable corresponds phenotype dependent 100% on genes

This is not correct. It means 100% of the phenotypic variation depends on genes, which is quite different. As a classic example, the heritability of "leggedness" in humans is very low, close to 0. This is because when people don't have two legs, it is usually for environmental reasons (accidents, amputation etc.). However, I'm sure you would agree that having two legs is specified in the human genome.

Heritability is not a conditional probability as you describe it (I know of no such statistic, although I suppose you could empirically calculate one). It is more like a r^2 value in statistics if you are familiar with that.

Another note - h^2 is not necessarily fixed, and only applies in a particular environmental context. Change the environment, and you could in theory change h^2.


chazwomaq t1_j5605rv wrote

You might want to look in Fisherian runaway selection and Zahavian honest signalling. Both are explanations for the evolution of preferences for sexually selected traits, but would take a while to write out here. Wikipedia is good.

Such traits don't need to offer a survival advantage to evolve. In fact, many examples probably offer a survival disadvantage.


chazwomaq t1_j529ba1 wrote

This statement. although 25+ years old, is still pretty good.

If you take a whole bunch of things that people have to learn to do (e.g. maths, spelling, logic, speed of thought, and memory), they all correlate pretty well together. So psychologists call this statistical manifold "g" for "general intelligence".

Theories like Gardner's multiple intelligences are frankly nonsensical because it ignores statistical reality, and replaces the word "talent" or "ability" with "intelligence". Thus he refers to intelligent (meaning good) dancers with a straight face.

The biological basis of intelligence is largely unknown, although brain size, number of neurons, and amount of folding is correlated.

Cognitive abilities like how much you can hold in your working memory, and how quickly you can make decisions, although correlate and plausibly cause intelligence differences.


chazwomaq t1_j520xuv wrote

Humans do show size dimorphism (about 15%), albeit not as much as some other primates, and certainly not as much as elephant seals. There is also substantial dimorphism in upper body musculature relative to lower body, suggesting adaptations for fighting.

The rest of what you described is Darwin's male-male competition and female choice.


chazwomaq t1_j4w6v81 wrote

Where one sex (usually males) competes physically for the other sex, there is selection pressure for large size, musculature, weaponry like antlers and horns, territoriality, and aggression. The winners of these contests reap huge rewards in terms of mating (Bateman's principle), which is why sexual dimorphism is associated with polygyny. In monogamous species, there is much less incentive to invest energy into intrasexual competition.


chazwomaq t1_izw4vqt wrote

Oh that's interesting I didn't know about this study. However, on reading it, rCBF doesn't look precise enough for individual level diagnosis. To rely on that alone would probably yield loads of false positives and miss many true positives. And since people often know they have depression as its symptoms are subjective, a pencil and paper test seems much more efficient.

But perhaps in the future biomarker(s) will prove accurate for psychological conditions.


chazwomaq t1_iztb6ls wrote

No. No such scans or biomarkers exist. This is true for most psychological conditions, in fact. The broken bone analogy is not quite right, because we do scan the brain to look for lesions (damaged areas), or tumours, or swelling.

The physical basis of most psychological and psychiatric conditions is largely unknown, probably because it is on a much smaller, subtler, and more complex scale than broken bones or biochemical levels.

A brief read here:

Will we have physical diagnosis in the future? Perhaps, but it's worth noting that there is not bright line dividing autism or ADD from non-clinical symptoms. They are the extreme ends of a distribution of behaviour on which everybody lies somewhere. Again, this is true for many psychological conditions.


chazwomaq t1_izkplro wrote

Some good answers here about the same cortical regions being active when perceiving and when imagining. Be aware though that this does not mean the whole pattern of activity is the same. For example, the optic nerves and thalamus are involved in sending visual information to the visual cortex. These would not be active when imagining.


chazwomaq t1_izf504y wrote

No, not a thing. As you describe them, these "core" memories would be part of autobiographical memory (memory about oneself). But there is no limited number of particularly special autobiographical memories that define people typically. A possible exception is a highly traumatic event.

Another slightly similar concept is a "flashbulb" memory, where people remember a particular event very clearly (although not always accurately). Classic examples would be the moon landings, Challenger disaster, or 9/11/2001. There are often not autobiographical though, but they might be highly emotional.


chazwomaq t1_ixzfaoy wrote

>From an evolutionary perspective, you want to grow to sexual maturity as quickly as possible,

This is not true. There is a tradeoff between reproducing early and growing a large body size. Both are advantageous, and so life history theory is all about managing such tradeoffs to maximise overall fitness.

Early sexual maturity (and small body size) is favoured when extrinsic mortality is high, and vice versa.