Identical twins are not so identical, study suggests
theguardian.com
theguardian.com
In my experience from meeting other identical twins in high school, you're either basically the same or polar opposites. There's rarely a set of twins that are in-between (although perhaps one could say the differences in the polar opposite twins become less pronounced with age).
Don't have a source right now but I remember because we wondered if we should take a test as well. In retrospect (now 40+ years old and still looking very similar) it's hard to understand why we every doubted.
For instance, that certain gene combinations that may present advantages for not the individual, but the individuals mother, grandparents, or other family members.
It doesn't seem to be well-known, but concordance for homosexuality in identical twins is very low (if memory serves, around 40%) compared to concordance for virtually anything else you can measure.
This is pretty unsurprising looking at the biological fundamentals -- a quick naive approach would be to predict "genes will never code for homosexuality, because it is such a crippling failure for the organism" -- but it does tend to undermine the idea that homosexuality is biological in origin.
Lets make witchcraft a part of medicine then. A statistically significant part of the human population belives in it. Lets get that into a 4 semester course in a 6 year medical degree.
Genetics affects everything including the environmental influences you are subject to. But your genes are trying as hard as they can to ensure you are heterosexual.
25% of the variance in sexuality is genetic or heritable. Compared to approx. 80% for intelligence. A small genetic component, but it seems as if experiences are the major deciding factor for sexuality.
80%+ is what the current corpus of scientific knowledge says. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4270739/ Here's a somewhat good primer on the topic, but the wikipedia page on heritability of intelligence (and it's sources) is also somewhat good.
Intelligence is a notoriously hard thing to define and measure, and I think it's more easily predicted by environmental factors than genetics. The idea that smart people breed and have smart children and that's why some people are smart and others are dumb, is more of a cop-out, since predictors of success that tests like IQ try to explain are more accurately explained by socio-economic factors.
Basically this has no real world implications. I realise this isn't the argument you were trying to make necessarily, you were just pointing out a perceived 'fact', but it lacks a lot of nuance that could lead to dangerous assumptions about the real world, especially since you related it to sexuality.
People have no clue how much more rigorous these studies than anything else in the field and adjacent fields.
Only in young children. The correlation vanishes as the children age. You were wise to delete this remark from your comment.
> Don't think I'm not aware of the history and research of this area.
Heh.
First you try to insinuate that IQ is not related to intelligence and even if it were intelligence has not practical application in the "real world".
Your first point was disputed by the comments related to how rigorously this subject is studied and documented, due to it being a third-rail area of academia.
I am going to dispute your second point myself. That rigorous study and documentation associates IQ with intelligence and intelligence with 'g' which, although not precisely defined, is associated with (at least) higher problem-solving ability.
So now your argument reduces to "higher problem-solving ability has no practical application in the 'real world'".
And so I will just dispute that statement out of hand because problem-solving ability is what has allowed humans to become the dominant animal on Earth.
If you think that IQ studies are inadequate, don’t even look at other fields that study humans (aside maybe from double blind trials in medicine), you are going to have a heart attack.
By your standards we need to ignore 90% of academia and solely rely on physics research to guide our policy.
I think the idea that we can control properly is extremely unlikely and IQ will turn out to be a lot difficult to extract from learning/society/environment than you might think, especially as findings with epigenetics and intelligence start to be shown. https://www.europeanscientist.com/en/research/epigenetics-an...
As for cultural loading in intelligence tests, maybe you could expand on that? How do you measure how much culture was involved in the methodology, and how it affected the results of the tests?
The range of SAT scores at a US prep academy populated with the progeny of relatively closely related families will be substantially determined by heritable differences between individuals. Outside of that, it's disingenuous and irresponsible to throw out that 80% figure as a general measure of intelligence heritability. In fact, not even the studies say that: 80% is the measure for middle-aged and senior adults. For everyone else, even their measures are substantially lower.
Can you explain that more in depth? To me that is counterintuitive. If there is a group of closely related people, I would expect their differences to be due to environment, rather than genetics, because they have similar genetics.
Remember that the heritable component of intelligence is polygenetic; it'd not determined by the presence of a single SNP, and two people could have similar intelligence originated in very different genetic profiles. People who are relatively closely related will have similar profiles that interact with the similar or shared environments in similar ways, meaning that the effect of small genetic differences will be more pronounced. Someone with the same "potential" for IQ, but from a different set of intelligence-related genes, interacting with the same environment might be said to have had the heritable component of their IQ become less efficacious.
For example, nutrition is a component in IQ. Everyone at this school is able to drink milk and benefit from the nutrition value-add. Someone less related to the other students also attends the school; they're lactose-intolerant, but benefit from eating certain fruits native to their homeland. The school doesn't serve such fruits, but it does serve milk. The student subsequently tests at a lower IQ. I would say at this point that variation between the LP students' intelligence is likely to be more related to genetics than is the variation between their IQ and this lone student's, which has a more substantial environmental component.
[1] the odds of having a gay son increase from approximately 2% for the first born son, to 3% for the second, 5% for the third...
[1] https://en.m.wikipedia.org/wiki/Fraternal_birth_order_and_ma...
I have heard at least of the idea that a non reproducing sibling can help you raise your own offspring, who will have mostly the same genes. This is corroborated if I recall correctly by findings that each new child in a family has more chance to be homosexual than their already born siblings.
There is also the idea that there might be genes that are most of the time favorable to reproduction, but once in a while (through crossing or mutations) result in homosexuality.
Very radical approach, seemingly against the grain of what we observe in the wild. It's such a leap of logic, you may very well have been talking about how santa claus' reindeer achieve thrust for their impressive levitation.
Unless you have some solid papers or anecdotal experiences that say otherwise I'm willing to change my stance.
My initial response was to the above statement which to my eyes presupposes homosexuality to be genetically expressed. Which has nothing to do with social/environmental factors.
Of course it is possible that statistically each new child in a family has higher probability to be homosexual for environmental reasons, but for genetic reasons? I don't see it (could be wrong, not an expert at all)
Edit after reading: apparently it's well studied and proven that each subsequent _male_ child has more chance to be homosexual and that "the fraternal birth order effect operates through a biological mechanism during prenatal life, not during childhood or adolescence"
Not genetic and not biological are two different things. E.g. the differentiator might be hormonal influence during the fetal stage. See https://en.wikipedia.org/wiki/Epigenetics for a long list of things other than DNA that can affect how organisms develop.
It's not necessarily a failure for the gene just because the organism doesn't reproduce. Genes extend beyond the organism to the family.
It would be more surprising that it persisted in less social species.
It does.
This is just a homophobic mischaracterisation of sexuality.
I recognise and don't appreciate how much of an effort you made to fit this homophobia into your point.
Also, 40% heritability is informally considered to be a high genetic component, not "very low", and e.g. heritability of eyebrow thickness is 37%.
I’ve personally always wondered if there could be tribe-level selection for tribes with some non-heterosexual members.
But I also have personal experience, and I’ve met others who do as well, with life experiences that make me wonder if they could somehow affect sexuality. I know it might be presumptuous of me to consider the idea, but it’s only just an idea—one I usually keep to myself.
- there's literally nothing to stop a homosexual person from biologically reproducing,
- it assumes that the only value of an organism is in its Darwinian fitness (its ability to reproduce), which is pretty gross. I reject this assumption.
The parent appears to be applying this heuristic of value only so far as it implies a moral failure of homosexuality: it's not a typical measure of value. Humans value other animals more highly than this, without regard to whether they have reproduced.
Besides, close relatives in the animal kingdom (Bonobo) use significant amounts of sexual behavior in their sociality, including same-sex interactions. Unfortunately we evolved from chimpanzees, who have strongly abusive and hierarchical social structure. Whence, nasty homophobic comments.
It’s quite astonishing how much bonobos look and act like humans when they walk upright or when they play with their babies.
In fact, one could say that the benefits of such an alternate sexuality were so recognized that some societies sought to produce it artificially through the creation of eunuchs.
Colloquially the family has always called them mirror image twins, because coincidentally they had some early moles on their face that happened to be on opposite sides from each other, but IIRC the term actually means something else. They are in fact monozygotic.
https://en.wikipedia.org/wiki/Swedish_Twin_Registry
> The Swedish Twin Registry (abbreviated STR) is a twin registry based at the Karolinska Institutet in Stockholm, Sweden. Originally established in the 1960s, it is the largest twin registry in the world. It is widely used for medical research, with about thirty active research projects using data from the study as of 2019. As of 2012, it contained a total of 194,000 twins, 75,000 of whom were of a known zygosity. In principle, it contains records of every twin born in Sweden since 1886.
Edit: A fascinating list of publications from ~2000 and onwards: https://ki.se/en/media/84204/download (PDF, 1100+ records)
Piqued my interest. Didn't realise there were so many types of twins. Superfetation just seems incredible to me. I'm just thinking of the perfect combination to produce the maximum amount of offspring for a woman. A quick google says the greatest officially recorded number of children born to one mother is 69, to the wife of Feodor Vassilyev (b. 1707–c.1782), a peasant from Shuya, Russia. In 27 confinements she gave birth to 16 pairs of twins, seven sets of triplets and four sets of quadruplets.
If we involved superfetation in Feodor's nameless wife we could trivially improve the output by a huge amount.
I would guess is has to do with exposure and knowing them from an early age. It's weird how that works, but I imagine parents of identical twins can very easily tell the difference, so there must be some major difference. Recently, I met another pair of twins and I couldn't tell the difference between them either. It must be extremely nuanced and only obvious to people who have been around both twins for a while. I would guess that it would be easier as twins get older and diverge in physical ways (body fat, muscles, and other physical traits).
Complex traits usually converge towards 50/50 because that's what you expect when the question is framed wrong. Different genes activate based on input from the environment.
Precisely. Traits feed back and feed forward, etc. You cannot simply say 30% genes and 70% environment because you cannot ignore how they interact with each other.
Does "anyone" really think that? I, who's well more versed in sciency things than the average although I never really thought about this particular subject, would have guessed that they have the same genetic code. So yes, I'd guess that a big proportion of people would think that
http://www.econtalk.org/michael-blastland-on-the-hidden-half...
I have fraternal twins. They are not at all that similar! Not in looks, or size, or hair color, or personality. They're only ~2 years old and the differences between them, both physically and mentally, is so staggering, already.
Life is so fascinating!
Completely insane mechanism that alters DNA of our cells in their lifetime in useless and dangerous way just because for DNA/RNA sequence to survive and spread it's sufficient that is figured out how to copy itself.
My another recent interesting read: viroids.
For example, if you plant identical trees, will they grow their branches identically, even in a very strictly controlled environment? I guess not.
Obviously to whom? I was taught that DNA has a chance of mutating each time it's copied, but that's certainly not "obvious".
> They measured mutations that occurred during embryonic growth and found that identical twins differed by an average of 5.2 early developmental mutations. In 15% of twins, the number of diverging mutations was higher.
That was the theory proposed as to why identical twins have different fingerprints. Slightly different conditions in the womb result in slightly different fingerprints.