# Some Biology Related Things I Found Interesting

Here are some things I learned over the last year that past me would have found somewhat non-obvious or that were surprising to me at the time:

- New genes are usually not evolved from scratch one basepair at a time.
  - The first evolutionary biology textbook that I picked up after learning that [textbooks are the fast way to learn](https://www.lesswrong.com/posts/xg3hXCYQPJkwHyik2/the-best-textbooks-on-every-subject) talked about some basic maths for how traits spread through a population once they evolve, depending on their fitness both in asexual and sexual reproduction. Essentially, very similar things that are covered in the [simple math of evolution](https://www.lesswrong.com/s/MH2b8NfWv22dBtrs8) sequence. One thing that went unmentioned in both of these, as far as I remember, was what mutations usually look like. Most mutations are simple single-nucleotide mutations, but new genes usually develop when an existing gene is copied. So not only do organisms have ancestors, genes can be organised in families too! This allows evolution to do code reuse for common patterns. For example, having an interface for your enzyme to use ATP to perform work.
- The ancestral environment is not (only) the Savannah
  - When thinking about why humans have lungs, I think most would notice that, thinking about how this came to be, it makes sense to think less about the savannah and more about what was easy for fish to develop as they make their way out of the water. But somehow, when it comes to psychology, there's a tendency for people to only think about our most recent evolutionary history in the savannah. When reasoning about why humans feel loneliness, don't only think about the human ancestral environment. [Mice feel lonely too](https://www.nature.com/articles/s41586-025-08617-8)!  
  - I noticed this bias in myself. Recently, when I sat on the toilet, when I had not been peeing for a while, I noticed that peeing is rewarding? What the hell?! How did enough of my (human) non-ancestors die because peeing wasn't rewarding enough? The answer is they weren't homo sapiens or hominids at all. Maybe this is not even that much of a shared human experience? It seems especially weird that the reward seems stronger the stronger the urge to pee was beforehand. Maybe this is just part of a larger machinery where your nervous system hands out a reward when you satisfy a strong urge (homeostatic feedback control circuit) back to homeostasis?
- [Evolution is cleverer than you are](https://en.wikipedia.org/wiki/Orgel%27s_rules)
  - [The machinery for repair by homologous recombination is just insane](https://www.youtube.com/watch?v=Xe-83tBcxhs)
  - Think about it before clicking the links: How would you [make sure](https://en.wikipedia.org/wiki/Topoisomerase) [DNA doesn't get as tangled as cabled earphones](https://en.wikipedia.org/wiki/Nucleosome)?
- There are about ~100-200 different neurotransmitters our brains use. I was surprised to find out that I could not find a single neurotransmitter that is not shared between humans and mice (let me know if you can find one, though). An example of [interfaces as a scarce resource](https://www.lesswrong.com/posts/hyShz2ABiKX56j5tJ/interfaces-as-a-scarce-resource)?
- Metabolism is similarly constrained, and only the most useful things hang around in the genome: 
  - glucose bonded with fructose => sucrose: a high-energy compound that humans get a lot of energy out of
  - fructose bonded with fructose => [inulin](https://en.wikipedia.org/wiki/Inulin): high-energy compound that humans don't have an enzyme for, so it's considered healthy low-calorie fibre.
- Expanding on that previous point, sure Drexler-style diamondoids [might not](https://muireall.space/nanosystems/) [be practical](https://www.lesswrong.com/posts/FijbeqdovkgAusGgz/grey-goo-is-unlikely), but just making ribosomes with an expanded/alternative amino acid alphabet would presumably unlock you all kinds of neat materials you couldn't make efficiently before. Or just genetically engineering existing developmental biology machinery to grow you whatever you need.