- John H. Rutherford – The concept that major evolutionary changes tend to take place in stages not all at once” is called mosaic evolution
- Harry Nelson and Robert Jurmain : Mosaic evolution is a term “applied when the rate of evolution in one functional system varies from other systems.
Mosaic evolution refers to the differential evolution of component parts of an organism. All parts of an organism do not change at the same rate in the course of evolution and at the same time period.
Human evolution, for example, shows a mosaic evolution. Not all parts of a human being evolved at the same time and at the same rate. In 1959, Wilfrid Le Gros Clark , first applied the term mosaic evolution to describe this disjunction between brain and locomotor evolution in the australopiths. the early evolution of bipedalism in Australopithecines, and its modification of the pelvic girdle took place well before there was any significant change in the skull, or brain size. The foot and pelvis of ancestors of humans were clearly transformed from Quadrapedal to bipedal types in relatively short time period. Then the skull particularly the brain case of humans changed relatively later than the bipedal structure once perfected. Afterwards Brain changed rapidly relative to further changes in the pelvis and foot.
D. J. Morton was perhaps the first to remark on this disjunction, noting that the Trinil Homo erectus material from Java combined a derived, human-like femur with a more primitive, small-brained skullcap. The proposition that bipedalism long preceded brain enlargement in human evolution was further confirmed by the discovery and description of the small-brained but bipedal Australopithecus fossils from South Africa
It is now commonly accepted that two of the most distinctive human characteristics—bipedalism and large brains —evolved at different rates and at different times in our lineage and that the disconnect between locomotion and encephalization extends into the Pliocene.
Using fossil record, dental shape showed mosaic evolution within the canine teeth found in early hominin. Although canine reduction has probably occurred prior to the evolution of Australopithecus, “changes in canine shape, in both crowns and roots, occurred in a mosaic fashion throughout the A. anamensis–afarensis lineage.
Importance of Mosaic Evolution
Mosaic evolution plays a key role in macro evolution in the following manner.
• It brings stage by stage change in different parts of an organism.
• It sets a flexible framework within which different organs have to grow and develop in relation to other parts of an organism.
• It can provide the maximum limit upto which a part of an organism can develop in time with the development of other parts in the body.
• It shows not only differential evolution but also the overall adaptive pattern on evolution of an organism