With Halloween only weeks away, the topics on this blog are getting darker.  I find it fascinating how art imitates life, even when the artists don’t understand the life they are imitating.  I doubt the writers of the original Friday the 13th movies (released in the 1980s) understood the concept of heritability, let alone the fact that heritability increases with age, and yet their main character, the iconic hockey mask wearing machete wielding killer, Jason, was a perfect example of exactly that.

In the late 20th century, it was discovered that genes explain about 45% of the IQ variation in childhood, 65% of the variation in adolescence, and about 80% in later maturity.  Family environment explains about 35% of the IQ variation in childhood, and near zero by later adulthood.  Meanwhile chance environment explains about 25% at all ages.

The character of Jason was born with extremely bad genes for IQ, a genetic condition called hydrocephalis, where there is too much cerebrospinal fluid in the brain, causing the head to swell and deform.  Yet despite his extremely bad genes, growing up he would have scored above 60 on IQ tests because his mother was constantly teaching him and getting him to participate in educational activities like summer camp.



The late actress Betsy Palmer was brilliant as Jason’s all American mother; the ultimate summer camp mom

However the problem with trying to educated people beyond their genetic ability, is that as soon as they are placed in a novel situation, they can’t adapt, and their learning and training is useless.  For Jason, that novel situation was going swimming one evening at Camp Crystal Lake.


Not intelligent enough to remember how to swim, he almost drowned and was washed to the other side of the lake.  When he came out of the water, in the unfamiliar wilderness, he could not adapt by finding his way back to the camp, let alone to his grieving mother.  So he simply lived in the woods like animal, for decades.

So he started with a great environment (being raised by an attentive all-American mother) which artificially propped his IQ up above 60, but because his genetic ability was so low, when faced with a truly novel problem (nearly drowning and washing up in an unfamiliar part of the woods), he turned the situation to his disadvantage, by getting stranded in the woods for decades and becoming a feral child, losing his capacity for speech.


So what started as extremely bad genes being propped up by a good environment (attentive mother) became extremely bad genes in an extremely bad environment (living like an animal in the woods).  This is a classic example of the gene-environment correlation increasing with age: bad genes create bad environments, even when they start with good environments.

This shows that while a good cultural environment can raise IQ scores, it can’t do much to raise real intelligence.  Because if real intelligence was being raised, why do genetically dull people from good environments see their IQs drop with age?  It’s not that the effects of environment fade, it’s that environmentally enhanced IQs were never real to begin with, which is precisely why they can’t maintain their good environments.

By the time Jason was in his 30s (my age), not only had his low genetic IQ destroyed his cultural environment (living in the woods devoid of all culture) but he had finally destroyed his biological environment, as his violent behavior caused someone to sink a machete into his head, physically damaging his brain.



Such damage from the physical environment, like the cultural deprivation of becoming a feral child, damaged his IQ score, but unlike cultural deprivation, the biological insults destroy real intelligence, and not mere test performance.

Jason was born with a genetic IQ of perhaps 40, but because of a loving mother (good environment) he had a phenotypic IQ of over 60 in childhood.  But because the phenotypic IQ was artificially propped up by an environment he could not adapt to his advantage, his environment precipitously declined, until his IQ was as low as his genetic IQ.