No, that can't explain his result showing the witch gene going extinct despite, by stipulation, zero fitness impact on individuals but 100% transmission. Becaus

No, that can't explain his result showing the witch gene going extinct despite, by stipulation, zero fitness impact on individuals but 100% transmission. Because the human population did grow over that time, so every deadend must have been balanced out by even more children by the non-deadends. And since he starts at hefty fractions like '1% of the entire population' (and goes up to 20%), we should be well beyond any issues of very small number effects or gambler's ruin. There has to be something wrong with either the data or code. (It almost looks like a sign error!)