Reproductive isolation means that each other can't produce fertile offspring, including many situations, such as reproductive isolation before mating, that is to say, the reproductive time is different, the two species can't mate, the reproductive organs are different, and there is no way to mate, and there is gametic isolation, that is, sperm and eggs are not fertilized, or fertilized eggs can develop abnormally, which is called reproductive isolation.
Simply put, reproductive isolation means that close relatives who are related by blood can't have sex, and having sex in time can't produce offspring, otherwise it will have a great impact on future generations. Reproductive isolation actually comes from biology. This is also why the marriage law of our country prohibits direct blood relatives and collateral blood relatives from marrying within three generations, which is unfavorable to the health of future generations.