Sahak Ghorwal tagged me in another thread asking can you confirm that macro- and microevolution is the same thing? The thread is already somewhat off topic from its OP and has since changed topics again, I felt it made more sense to answer in a new thread. The terms microevolution and macroevolution refer in a qualitative way to how much a species has changed. In order to understand what makes them different you have to define your terms. Using google to get a quick pair of definitions nets these: Macroevolution: major evolutionary change. The term applies mainly to the evolution of whole taxonomic groups over long periods of time. Microevolution: evolutionary change within a species or small group of organisms, especially over a short period. neither of these definitions gets into the detail of how evolutionary theory works but it is clearly distinguishing on the basis of how much change has accumulated. The distinction between them is somewhat arbitrary and subjective, a species could technically evolve in isolation without spawning multiple taxa, but still change significantly enough to warrant the descriptor of macroevolution. At the end of such an evolutionary process it would be significantly different from the species that spawned it. Creationist groups are fond of claiming that changes in allele frequencies represent microevolution and the creation of new species are macroevolution, but even that explanation is simplifying the concept just a bit too much and also ignoring one key fact: the two terms describe different kinds of results produced by the exact same functional process. The functional units of variation are nucleotide sequences. The effects of variants depend on where the variation occurs in the genome. If it is part of a gene expression control sequence it can effect which cell types the gene product is expressed in, if it is within the gene itself, it can affect the function of the protein, where the cell sends the completed protein, etc. Changes can also occur to structures like telomeres and centromeres, and control regions that determine expression of large tracts of DNA via epigenetic marks. From here, successive levels of complexity such as embryonic development, cell-cell interactions, etc can make even a seemingly small change result in a significant effect. Ultimately at a fundemental level, the same process produces both microevolution and macroevolution. If you are trying to draw a distinction between variation within a single breeding population, and the splitting of 2 populations via inability or near total unwillingness to breed (or other things that would fall under concepts of speciation), that is a different, but related, question. evolution.berkeley.edu/evosite/evo101/VADefiningSpecies.shtml The most common species concept: evolution.berkeley.edu/evosite/evo101/VA1BioSpeciesConcept.shtml some others: evolution.berkeley.edu/evosite/evo101/VA2OtherSpeciesConcept.shtml Determination of what causes speciation depends on what speciation concept you are referring to. Under biological species concept any variation between two fragments of what was once a unified population that lead to difficulty in breeding can result in speciation even if the two species remain otherwise phenotypically identical. The variation could be behavioral, it could even be genetic (a simple incompatibility of sperm and egg surface proteins, or a shift in chromosomal content that results in incompatible chromosomes and hybrid breakdown). The reason that speciation tends to take a long time is due to the random nature of the generation of NEW variation within the gene pool. These changes must first occur and then be passed on to enough of the population that they come to dominate in the gene pool. Each change may incrementally shift the population away from successful mating compatibility from another sister population without significantly harming mating compatibility within its own population. (the male/female gametes and behaviors can co-evolve because the population is actively exchanging and recombining genes during mating, while no material is being shared with the sister population). Given enough time you EXPECT there to be a point at which genetic compatibility or behavioral compatibility is lost. The process, however, is exactly the same as the process that drive any other changes within the species over time. The distinction is arbitrary. You cannot correctly claim to accept microevolution and deny macroevolution, because the smaller one implies the bigger one. TLDR: They are only distinct due to how they are defined. Macroevolution is not simply speciation, it refers to something far more grand than that. Microevolution, speciation, and macroevolution are all results of the same process, they simply refer to different changes or different timescales.
Posted on: Wed, 31 Dec 2014 00:46:11 +0000
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