The morphological species concept groups species according to morphological similarities and ignores other differences such as DNA or inability to reproduce between individuals. The morphological species concept stems from the morphology, which is the study of the physical aspects of an organism and their arrangement.
Morphology is essentially the study of the structure of the parts of organisms. Morphologists focus on understanding the arrangement of parts including external physical characteristics as well as internal organs, systems and bone structures. Unlike physiology, which focuses on the function of the parts of an organism, morphology seeks only to understand and classify the parts and their arrangement in various organisms. A morphological species is classified based solely on morphology or structure. According to the morphological species concept, a morphologist would use size, shape, color and structure of one organism and compare it to another to determine its species. While it is true that variation among closely related organisms are fewer than those among distantly related organisms, the morphological species concept ignores some important aspects of organism development used to classify species. Some species are structurally similar, but are genetically distinct creatures. These creatures are referred to as cryptic species. Following only the morphological species concept, these creatures would be classified as a single species despite vast genetic differences. However, almost all scientists use some amount of morphology in classifying and distinguishing species as physical form and structure are key components of understanding organisms.