Growing up, I read a lot of science fiction. It exposed me to a wide range of ideas - weird cultures, strange technology, odd circumstances. Isaac Asimov wrote an essay about how the best science fiction didn't just imagine a new idea, but the consequences. Not just the automobile, but parking lots and traffic jams. Some science fiction predicted rapidly-accelerating technology curves.
But one thing I can't recall seeing predicted is a particular effect of rapidly-developing technology - overlapping generations of technology.
For most of human history, technological advances happened at a slow-enough pace that one had time to spread before another arose, at least within a particular culture. It took a few thousand years for stoneworking to mature. Then came bronze, and then iron. Arrows, crossbows, etc. A group might get a short-term advantage, but the tech would spread soon enough, and a new equilibrium would be established.
But that hasn't been true since at least the last half of the twentieth century. And the most clear illustration of this is modern public restrooms.
There are at least three potential flushing mechanisms in common use - manual control (lever or button or whatever), interval timer (e.g. every ten minutes or so), or some kind of sensor-triggered system (usually infrared). For faucets, there's hand-turned valves, pushbuttons (that run for a fixed time, then shut off by themselves), or infrared sensors. And then there's drying your hands - could be a long cloth towel on a roll (still in a few places), paper towels, air dryers (button or sensor driven, even the new 'Dyson air blade' models), and so forth.
And they're not all installed in any kind of order. The technologies are mix-and-match. You might have infrared flushing, hand-operated faucets, and paper towels. Or manual flushing, infrared-controlled faucets, and air dryers. In any combination. You walk into an unfamaliar public bathroom these days, you literally have no idea at all what tech you'll be using to carry out your business.
Cell phones are like that, too, of course. We have everything from simple 'dumb phones' to 'feature phones' to 'smart phones', in a huge mix. But bathrooms show it most clearly. New innovations and methods arrive so fast they don't have time to replace the 'old' tech before the next big thing appears. I can't recall a story before the 2000's that really anticipated that wrinkle.
...aside from the fact that they appear to be impossible, that is. Don't misunderstand me, here: I don't really think, say, telekinesis is real or even possible. But if there were some way for the brain to directly perceive and affect reality, that'd seem to be a neat trick. Why wouldn't it be incredibly common, if it's possible at all? 'Neat tricks' like eyes developed independently dozens of times. Why don't we have psychic clams as well as people?
Other people have proposed that psychic powers must therefore be useless. But let's assume that they would be useful. There's still a major problem with them; at least, the flashier powers like telekinesis and such, the ones that actually do something as opposed to sense something.
An interesting fact: When you sleep, and dream that you're, say, running... your brain actually tells your legs to move. EEGs show this. Fortunately, there's a bunch of cells at the base of the brain, in the brainstem, that acts like a cutoff switch. When you're asleep, it blocks those signals from getting out and causing your body to move. Note that this system isn't perfect. Sometimes it doesn't 'reconnect' immediately when you wake up, and you get Sleep Paralysis. Or it doesn't engage properly while you're asleep, and you get Sleepwalking.
Now, let's consider psychic powers, like telekinesis. Okay, by whatever mechanism, your brain can directly move things in the outside world, without using your body to do it. So... a clump of cells in the brainstem isn't going to block your TK. It'd be like you were always "sleep TKing". Your telekinesis would be danger to yourself and others, in direct proportion to how powerful it was. No matter how useful it was during the day, as soon as you doze off it's very likely to kill you.
An interesting fact: in humans, males are conceived significantly more often than females - a rate of about 120 to 100. But at birth, the ratio is about 106 to 100. I.e. male fetuses miscarry more often than female ones do. Developing a male is apparently over 10% riskier than developing a female. Why should that be?
One reason is simple genetics. Females have two X chromosomes, and males have an X and a Y. The Y chromosome is pretty small and doesn't contain many genes. The X chromosome contains quite a few important genes, on the other hand. If there's a harmful mutation on one X chromosome, a good copy on the female's other X can often compensate. Males don't have any backup, though. This is one reason why more men have color blindness than women, for example.
But there's more to it than that. It seems the basic body plan of humans (and mammals in general) is female. In fetal genital development, one hormone (testosterone) is necessary to initiate the formation of male genitals, and another (AMH) is necessary to inhibit the development of female ones.
If the functioning of the Y chromosome is disturbed in some way early in fetal development, a (to all outward appearances normal) girl may be produced who is genetically male. (For examples of this, see Swyer Syndrome, or Androgen Insensitivity Syndrome.)
So, by 'default', an embryo will develop as female unless an active set of operations is undertaken to 'turn' the embryo into a male. Physically becoming a male is a more complex and complicated process than becoming a female. As in the case of testosterone and AMH above, it's a matter of both encouraging male developmental pathways and suppressing female ones.
Why should this be any different in brain development? There are sexual dimorphisms (on average) in portions of the brain. The corpus callosum tends to be thicker in females and many areas of the hypothalamus are altered in males - and one area, the Sexually Dimorphic Nucleus, is practically nonexistent in females.
Now, I have a background in engineering - when I hear about how 'complex' a system is, the first thing I think of is 'that means it has more ways to go wrong'. The simpler you can make a design, all other things being equal, the more reliable it will be. And the more complicated you make a design, the less reliable it will be.
So we would expect male sexuality to be more fragile, to have more problems - at the very least to have more diversity - than that of females. From everything I've heard, this is in fact the case. I gather that male homosexuality is more common than lesbianism, and that sexual fetishes and 'perversions' are much more common among males than females.
Protiens are the basic structural material of life on Earth. They are composed of LEGO-like building blocks called amino acids. These amino acid units connect to each other end-to-end, like train cars, in long strings. But then, once constructed, they curl up and kink and twist and form three-dimensional structures. Those 3D structures then go on to make muscles and tendons and eyes and skin and everything else in the body.
How does the body know how to make proteins? They are described in DNA. DNA is another long molecule made of building blocks - in this case, only four types. These building blocks, the "nucleotides", come in groups of three, and these triplets specify particular amino acids. The whole DNA molecule is a long string that just specifies the sequences of amino acids needed to build various proteins.
So, you have essentially one-dimensional sequences made of a small number of symbols, maybe a couple of dozen. These are 'read off' and twist and combine and react to form complicated, dynamic, and functional structures.
It occurred to me once that text is like that. You have about as many letters in the Roman alphabet as there are amino acids, and they are read in a straight, linear sequence. But as they are read, they interact with each other and the ideas and experiences already in our minds, forming complex, elaborate, and active concepts.
More, a strand of DNA in isolation does nothing, it's meaningless. It only becomes active - it only has a meaning - when it's 'read' by a whole complex cell around it. Similarly, a book by itself does nothing. It is only when interacting with a reader that it takes on meaning, that it becomes something more than just ink on paper.