Define 'illegal' in this context and whether or not you are talking about grade school, high school or college.
There are no effective laws banning such education. There are a few local laws that insist evolution theory in grade and high schools be balanced with disclaimers suggesting the theory is weak and other options should be included in science classrooms.
But when challenged in court, the laws are almost universally overturned.
Kitzmiller v Dover School District settled the case.
That's good to know
I was going by news reports (on the UK news) from probably more than 15 years ago now that one state (Kentucky?) had banned the teaching of evolution in schools (I took that to mean classes from kindergarten to 12th grade) - but it's good to know that it was never as bad as that and these laws get overturned.
At the university level, some private religious universities deny evolution theory is valid.
Liberty University Creation Studies
Liberty is a religious indoctrination university established by Jerry Falwell.
To my horror they have a 4-year nursing degree, teaching nurses that evolution isn't a valid theory.
I've heard of places like that. I didn't know they were allowed to award actual validated degrees though. That's very worrying.
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general rant (not aimed at any individual post)
Evolutionary biology has so much to offer medicine and it's a very poorly understood area. Many genetic illnesses are caused by genes that had an evolutionary advantage in the past but don't work quite the same way in the modern world. Like allergies and Crohn's disease - thought to have evolved to give protection against internal parasites, but when the body has no parasites they make the body attack itself. Crohn's disease genes have been found in Neandertals, along with several other genes that aren't so good for modern people. Understanding what the original benefit of the gene can help find treatments, but it doesn't seem like very much research is going into this aspect of disease.
I just skim-read the Wikipedia article on Crohn's disease and found just one sentence about this "
Another study has theorized that the human immune system traditionally evolved with the presence of parasites inside the body, and that the lack thereof due to modern hygiene standards has weakened the immune system. Test subjects were reintroduced to harmless parasites, with positive response" and no mention of the fact that a gene for Crohn's disease has been found in Neandertals. In spite of the fact that the study showed the treatment to be successful, it just got ONE sentence. This kind of sums up the whole thing.
Research into allergies has recently found that a particular species of gut bacteria stops people with the allergy gene developing allergies as long as they're exposed to it in infancy, and also that combining exposure treatment (where they give tiny doses of the allergen in an attempt to desensitise the person) is a lot more effective when combined with giving the person this bacteria species as a probiotic.
Some mental illness such as PTSD and CPTSD could be a lot better understood in an evolutionary context, viewed as adaptive responses to life threatening situations. PTSD could be seen as a useful adapted response to an external threat, e.g. predators, enemy humans. CPTSD could be seen as a set of adaptive responses to enable primates to survive being the "omega" of their own group (omega = lowest ranking, the one everyone else picks on), i.e. living alongside a constant, ongoing threat to their survival, on a knife edge between being cast out and dying alone in the wilderness (social primates, especially humans*, rely on the group for survival) and the threat of finally being killed off by members of your own troop/tribe. It also explains why it's so extremely hard for victims of abuse within their own families to leave - millions of years of evolution of survival instincts to stay with the group because death is more likely if you leave your troop/tribe and try to survive alone than if you stay and endure the abuse. This knowledge could be applied to help people leave abusive families, abusive social groups (like religious cults, etc) and so on, but most people don't even think of it because they know fuck all about how our ancestors lived. They just blame the victims: "well why didn't you just leave?"
Note: the above about PTSD/CPTSD is not the whole picture, it's a lot more complex than that, but I think there's a strong case to be made that the above is at least part of the picture and should be further researched and considered a lot more especially when it comes to helping people.
And that's before we get onto things like why bisexuality and homosexuality evolved and how this helped early human societies survive.
There are so many things that make more sense with evolutionary biology, and so much of it can be applied to help modern people deal with modern illnesses and modern situation... but even most people who "believe" in evolution know very little about actual human evolution. They believe our ancestors were knuckle-dragging brutes that were stupid and unable to talk.
Our whole understanding of humanity and what is "default" for our species and what is the result of culture and modern problems like overpopulation/trying to live in much greater numbers than we evolved for would be of great benefit to humanity. I would take hunter-gatherer as default for the species for the simple reason we spent over 2 million years being hunter-gatherers, we went from australopith to human and from
Homo ergaster* to
Homo sapiens sapiens as hunter-gatherers and agriculture only started 10,000 years ago, which is a mere blink of the eye. But how many people know even the most basic things about hunter-gatherer society? Their heads are full of a bunch of racist and completely inaccurate myths.
*going by the latest theories of high diversity/variation in early humans, which would mean all the early species like
H. habilis,
H. rudolphensis and
H. ergaster are all in fact the same species, which I think should be called
Homo ergaster, but there are rules about how they should be named and I don't know which name it would be going by the rules, but I like
Homo ergaster the best, so there
Also, sorry for the long rant, but another thing... when people try to find evolutionary reasons for things, they need to first be well enough versed in modern theories of human evolution before doing so. I have lost count of how many times psychologists do this just because it's trendy in psychology. Okay, it's good that they appreciate the importance of evolutionary biology. BUT they make such basic, fundamental mistakes that I want to bang my head against a brick wall. It's either a) they've taken a study on young, white, mostly middle class people from modern USA and extrapolated it to the whole entire human genus*, or even the whole of hominins*!! (You have to prove that the same effects is seen in all human populations including recently-contacted hunter-gatherers that have yet to be influenced by western culture before you can extrapolate it to the whole of
Homo sapiens sapiens, nevermind extrapolating) or b) they're interpreting it in light of theories that were disproven decades ago. Or, quite often, both of them at the same time.
*they don't realise they're extrapolating it that far, but if you're discussing things like why men don't like shopping (apparently because they evolved as hunters) then you're talking about the whole human genus. If you're talking about the evolution of bipedalism, you're talking about the entire hominin clade. But often they don't know enough about evolutionary biology to realise they're doing this. Plus they're taking the whole thing of "white young cis het USA male" being the default for all humans to the extremes of extremes.
Okay rant really is over now. I wish so much so much so much that evolutionary biology was a) taught so much better b) taught in so many more science courses - especially psychology!! - and c) much more valued generally.