retrogression

The act of going backward; retrogradation.

In astronomy, same as retrogradation.

In biology, backward development; degeneration; retrograde metamorphosis.

The act of retrograding, or going backward; retrogradation.

Backward development; a passing from a higher to a lower state of organization or structure, as when an animal, approaching maturity, becomes less highly organized than would be expected from its earlier stages or known relationship. Called also retrograde development, and regressive metamorphism.

A deterioration or decline to a previous state

A return to a less complex condition

returning to a former state

passing from a more complex to a simpler biological form