Major new features [in biological evolution]

Traditional groupings of living organisms into kingdoms and phyla are typically defined by the presence of major new features. Standard examples from higher animals include regulation of body temperature and internal gestation of young. Important examples from earlier in the history of life include nuclear membranes, sexual reproduction, multicellularity, protective shells and photosynthesis.

Trilobites are a fairly clear example of organisms where over the course of a few hundred million years the fossil record shows increases in apparent morphological complexity, followed by decreases. Something similar can be seen in the historical evolution of technological systems such as cars.