<span>Circadian rhythm</span>, also known as circadian clock or body clock is a biological process that follows a 24 hour cycle (approximately). It is said that circadian rhythm is dictated by natural factors in the body, as well as environmental signals.
This is allopatric speciation. The organisms were separated from each other by the containers. The separation caused them to evolve to the point that they were more likely to mate with each other than with a member of another tank.
