The evolution of the cellular slime molds

Abstract

The cellular slime molds have existed for a very long time; they have an ancient history. It is surprising that the early morphological species have not been supplanted and gone extinct, as is the case for larger organisms; a sizable number of ancient cellular slime molds still exist today-they are living fossils. This unusual phenomenon can be explained if one assumes that their morphology is only weakly affected by natural selection leading to a modest variation of morphology among the different species. I argue that the reason for their apparent relative immunity to the effects of natural selection can be explained by their small size; this is a general rule among all microorganisms.