passing from a more complex to a simpler biological form
同义词：degeneration
returning to a former state
同义词：regression, regress, reversion, retroversion
retrogression详细解释
ret.ro.gres.sion n.（名词）The act or process of deteriorating or declining.恶化：变糟的或衰败的行为或过程Biology A return to a less complex or more primitive state or stage.【生物学】 退化：向不太复杂的或更原始的状态或阶段的回归
