…Humans are genetic individuals. We are almost all completely unique, sharing at most one half of our DNA with our parents or siblings.

Humans are not special. Humans are not beautiful or unique snowflakes. Humans are the same decaying organic matter as everything else.

All humans have 99.5% of the same DNA, and some of that 0.5% is junk. According to Kyla, the correct interpretation of “siblings share half of their DNA” is as follows:

Don and Betty have two children, Sally and Bobby. For every one of Sally and Bobby’s nucleotide pairs, there is a 50% chance it was copied from Don and a 50% chance it was copied from Betty (except for Bobby’s Y chromosome). So you can say that only half their DNA shares the same origin. But since Don and Betty are 99.5%+ similar (more because they’re both white), Sally and Bobby will end having DNA that is mostly indistinguishable, regardless of its origin.

Selfish gene theory says that your behaviour is controlled by your genes to maximize the survival of identical genes, which is why you’re nicer to your relatives than to people with a different skin colour. Unless you assume that the few genes that differ between siblings are so powerful as to override all the rest, selfish gene theory is not sufficient to explain why people do things in their own interest that are against their relatives’. In fact, selfish gene theory leads to the same slippery slope as utilitarian ethics: you should sacrifice your life to make a bunch of rabbits happy. Potter is wrong that “If we were clones…there would be no need for morality”, because we practically are clones.

On the other hand, Potter is also wrong that twins or clones have identical DNA: genetics isn’t that simple.

There’s a popular theory in philosophy of mind that autism is caused by a deficiency in the “theory of mind module”: the part of your brain that allows you to figure out what other people are thinking and see things from their point of view. It’s suggested that schizophrenia could be an overactive theory of mind: hallucinations are leaks from simulation of other minds, paranoid delusions arise from assuming that other people are thinking about you, etc.

It strikes me as rather stereotypical, but autism has also been framed as an overly “masculine” brain: a focus on things and logical thinking over people and play. Schizophrenia could be correspondingly “feminine”: high empathy and poor logic skills.

There’s some correlation between autism and high physical growth, and between schizophrenia and low physical growth (all covered in this paper so thorough, it must have been written by an autistic). So guess what the proposed cause of this spectrum of disorders is? Genome imprinting: your mom’s genes are trying to make you schizophrenic and your dad’s genes are trying to make you autistic; if they’re balanced, you end up neurotypical.

In humans, the Prader-Willi and Angelman syndromes are caused by defects in a particular gene on the paternal and maternal chromosomes, respectively. Prader-Willi infants avoid breastfeeding and sleep a lot; around the age of weaning, they gain an insatiable appetite and interest in finding food (ie: do their own foraging and aren’t picky). Angelman children act extremely happy, getting greater emotional investment from their parents than their whiny siblings.

By far the biggest investment in growing a human fetus is the brain tissue, so we can assume that genome imprinting will turn out to be the cause of some neurological disorders…

For most chromosomes, a liger gets one from each parent. In highschool we’re taught that whether the mother’s gene or father’s gene gets activated depends on which one is “dominant”. That’s a gloss; genes don’t have dominance: both genes get activated and sometimes the effect of one is so powerful that it doesn’t matter what the other gene does. But if the lion gene says “grow to x” and the tiger gene says “grow to y”, it shouldn’t be the case that the liger grows to larger than both x and y.

I recently found out that the answer is a mechanism called genome imprinting: Chromosomes from each parent have different markers added by chromatin remodeling or methylation (together called epigenetics: I get the impression that which mechanism is unknown in almost all cases). There are genes that act differently or act on other genes differently depending on who they were inherited from.

So either lions have a maternally-imprinted gene and/or tigers have a paternally-imprinted gene that limits growth. And that’s why ligers are bred for their skills in magic.

Autocrine signalling

A cell transmits chemical signals that attach to its own chemical receivers

Post-translational modification

A cell produces proteins that modify the other completed proteins inside the cell (including prions, which are inheritable via reproductive cells)

Post-transcriptional regulation

A cell produces proteins that modify the way other proteins are assembled in the cell

Chromatin remodeling

A cell produces proteins that control how the machines access the DNA, including making parts of it inaccessible (probably inheritable)

Methylation

A cell produces proteins that make temporary changes to the DNA (by covering in a chemical that blocks the machines, which is totally inheritable)

“Copying errors“

Currently believed to be random mutations, I predict that proteins will be discovered that affect how DNA is copied

Reverse transcription

Proteins (including retrovirii) in the cell write new genes into the DNA (when these get inherited they’re called endogenous retrovirii)

Most of these mechanisms are very poorly understood and the more research that gets done in them, the more significant they appear to be versus vanilla genetics. This is why the Human Genome Project has failed to give us superpowers.

All this reminds me of a long time ago, when computers were really expensive, programmers would write programs that modify themselves while they ran. They are impossible to read (you can’t just look at the code), and only crazy people could write them, so it is now considered extremely bad programming. In other words, if there is a God, I wouldn’t hire Him.