Exactly, in a stable population, one offspring of each individual survives on average in an asexual species. Two with half of your genes each survive in a sexua

Exactly, in a stable population, one offspring of each individual survives on average in an asexual species. Two with half of your genes each survive in a sexual species. It doesn't need a long timescale, asexual species get out-evolved by sexual species and go extinct eventually. Sexual species have a much higher probability of entering new niches or surviving when the conditions change. This can be seen in many species that reproduce asexually when the conditions are good, but reproduce sexually when stressed. A species that loses the ability to reproduce sexually is doomed to extinction. Asexual reproduction is essentially putting all your eggs into one basket. When you die of a disease for example, chances are that most of your offspring dies as well AND there is a much higher chance that the disease adapts to your genome in the first place. This can be seen in agriculture, where plants are reproduced asexually to a much bigger extent than what would happen naturally. Many are impossible to grow without heavy doses of pesticides, as the diseases quickly adapted to the commonly planted strains. The strains need to be replaced every few decades, before growing them becomes essentially impossible, even with pesticides. Evolution is much faster than you assume.