It may also be that when the worms live in small mating groups, competition favors the evolution of large male sperm, but when there are a lot of females around, smaller sperm do a better job of ...

When two different species try to mate, they’ll almost always fail. Some, like horses and donkeys, will get lucky and produce hybrid offspring — but those mules are usually sterile. But for some worms ...

Different species are usually unsuccessful at interbreeding; if they do, the hybrid offspring is usually sterile. In this way, species are kept separate and the diversity of life is maintained. In a ...

When it comes to sex, animals have developed a plethora of tricks to avoid mixups with other species. They use sight, smell, and even feel to tell each other apart. But in certain cases, the ...