When Ectoparasites First Arrive and Adapt to the Fur or Feathery

Essay

When ectoparasites first arrive and adapt to the fur or feathery habitat of a host,they often lose more complex ancestral features.So it is possible to gain a trait in evolution and subsequently lose it.However,it is considered vastly improbable that this same trait will again re-evolve.Therefore,in trying to trace evolutionary lineages,can we always expect the most primitive forms to be the simplest and the most advanced to be the most complex? Why or why not?