The biologist John Berman has said that evolution is not an engineering process, so it often has limits that an engineer or other designer does not. Even if black leaves were better, evolution's limitations can prevent species from becoming as efficient as possible. Berman wrote that achieving pigments that work better than chlorophyll could be very difficult. In fact, all higher plants (embryophytes) are believed to have evolved from a common ancestor that is a sort of green algae – so chlorophyll has evolved only once (common ancestor).