Dyeing poison dart frog
Inside the new body of water, the tadpoles fight.  Sometimes they eat each other.  Usually, only one tadpole per body of water lives to become a new frog.  But sometimes there are two.  Scientists studied the fighting tadpoles.  They found that when one tadpole was much bigger than the other, they usually did not fight.  They believe this is because both tadpoles knew who would lose.  They also found that when two tadpoles in the same pool had the same parents, they only fought half as often as tadpoles that were not related to each other.