Traditionally, microevolution is defined as evolution within a species. That is microevolution involves small changes that do not create new species. On the other hand, macroevolution creates new species. With these definitions, the pictures across the top and down the right side of this page are both examples of macroevolution. This web site will show that while the variation across the top can be explained by natural selection, genetic drift and mutations the variation down the side cannot. In light of this observation, a better definition for microevolution and macroevolution is required. This web site will use the following definitions:
Microevolution are changes in the gene pool that do not create new genes. That is every gene in the new gene pool has a similar function and purpose in the original gene pool. A gene that is altered by mutations, but maintains its original function and purpose is called an allele. Alleles are different variations of the same gene. Microevolution creates new alleles. It does not create new genes. Macroevolution: changes in the gene pool that create new genes. Since new organs and structures require new genes, any evolutionary transition that involves a new structure or organ is an example of macroevolution.
The variation in the large cats across the top does not require new genes. Therefore, this variation is an example of microevolution. Traditional Darwinian principles can explain this variation. On the other hand, the variation down the right side requires new genes. This variation is an example of macroevolution. This web site will show that genetic drift and natural selection operating on the variation created by mutations cannot create new genes. Thus, the theory of evolution cannot explain the origin of new organs and structures, and evolution does not explain the origin of complexity.Why is the distinction between microevolution and macroevolution so important?
Experiments designed to test evolution always test microevolution. If macroevolution is possible it is too slow to be observed. So while the experimental evidence supporting microevolution is undeniable, the same cannot be said for macroevolution.
Scientists have theorised that given enough time microevolution can explain macroevolution. The logic behind this extrapolation rests on the traditional definitions for macroevolution and microevolution. New genes are not required for macroevolution as long as such evolution is limited to closely related species (for example - tigers and lions). In this example, the processes behind microevolution and macroevolution are identical and extending microevolution to explain macroevolution makes perfect sense.
On the other hand, this extrapolation is very hard to justify when microevolution is extended to explain the origin of new organs or structures. Since the evolution of new organs and structures requires new genes, microevolution can only be extended to explain macroevolution if the processes responsible for new alleles can also create new genes. Creating a new gene with a new function is clearly different than optimising a gene without changing its function (creating a new allele). So the first and foremost question at hand is can the processes that create new alleles also create new genes? Existing genes are not free to evolve into new genes.