Some modern species are apparently degenerate, not higher forms (Talk.Origins)
Evolution is supposed to advance species, but some modern species, such as many parasites and species living in caves, appear to be degenerate forms of other species.
(Talk.Origins quotes in blue)
1. Evolution adapts species to their environment. Sometimes that means becoming more complex, but not always. If losing a feature allows a species to survive better, the species likely will gradually lose the feature. Losing a feature is advantageous, for example, if the feature is energetically costly to grow and maintain (which is almost always the case) and if it serves no other function (which often happens when a population moves to a new environment, such as a cave).
No problem, the actual point is that the species we observe today are degenerate forms of the original members of their Created kinds.