It's funny hearing people talk about race science as a "pseudoscience" and then cite that humans share 99.9% of DNA.
We also share about 50% of our DNA with a banana and 98.8% with chimpanzees. Why? Because we are all eukaryotic organisms and most DNA is very old biological machinery that is responsible for the functions of life (copying DNA, making RNA, building proteins, generating and using energy, dividing cells and repairing damage, regulating metabolism, etc). We share that in common with all eukaryotic life.
But the human genome is enormous. Over 3 billion base pairs. Even a small percentage difference still represents millions of base pairs. Further, where those differences occur matters a great deal more than simply counting them. If some of those DNA differences result in instructions that say something like "develop this tissue in this way, at this stage, for this long", you can end up with resulting organisms that are dramatically different.
So it's not really about "percentage difference" when talking about genetic difference. A big part of the discussion must be about what genes switch on, where and how strongly they switch on, how long they stay on, what types of cells are expressing that, and at what developmental stage they are expressed.
Consider embryonic development. A single, small, regulatory alteration early in fetal development could produce a cascade of downstream consequences. If something were to, say, alter how neural progenitor cells proliferate during fetal development, you would not need thousands of new "brain genes" to produce a substantially different type of brain. You just need one single gene that changes the genetic instructions that govern how an organism develops.
So yes, humans are 99.9% genetically identical to each other in the ordinary single-nucleotide sense, but the remaining variation contributes to real and sometimes stark differences in physiology, appearance, temperament, etc. Even a tiny fraction of a percent has a lot of wiggle room and what can be done in that wiggle room is substantial.
Next time you see someone parroting the line that race doesn't exist because we are 99.9% genetically the same, you will know that person doesn't know shit about genetics and is just repeating a talking point they heard from someone else who doesn't know shit about genetics. They are not qualified to be part of the conversation.
Works by Cofnas are founded on pseudoscience. All humans share about 99.9% of their DNA. Visible traits like skin color are controlled by a tiny fraction of genes and do not map onto complex behavioral or intellectual traits.