A progressive change in the pattern of behaviour of a group of closely related organisms, the more complicated patterns often being associated with more recently evolved members of the group, which evolved from members exhibiting a more primitive pattern. For example, variations in courtship
behaviour among species of Hilara flies (Empididae) suggest an evolutionary lineage: (a)a male searches for a female and courts her in isolation;(b)a male captures a fly, presents it to a female, and she consumes it before mating;(c)a male captures a fly, joins a swarm of males, presents the fly to a female, and she consumes it before mating;(d)as (c
), but the male adds a few strands of silk to the fly before joining the swarm;(e)as (d
), but the male covers the fly in silk;(f)as (e
), but the male eats the edible portion of the fly, leaving the husk wrapped in silk;(g)males of non-carnivorous species use dried insect fragments or petals, around which they weave a silken balloon before joining the swarm;(h)the male makes only a balloon (i.e. containing nothing) before joining the swarm.