Maintained gene flow between two populations can also

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Maintained gene flow between two populations can also lead to a combination of the two gene pools, reducing the genetic variation between the two groups. It is for this reason that gene flow strongly acts against speciation , by recombining the gene pools of the groups, and thus, repairing the developing differences in genetic variation that would have led to full speciation and creation of daughter species. Microevolution is the occurrence of small-scale changes in allele frequencies in a population, over a few generations, also known as change at or below the species level [1] . These changes may be due to several processes: mutation , natural selection , gene flow , genetic drift and nonrandom mating . Macroevolution is a scale of analysis of evolution in separated gene pools . [1] Macroevolutionary studies focus on change that occurs at or above the level of species , in contrast with microevolution , [2] which refers to smaller evolutionary changes (typically described as changes in allele frequencies ) within a species or population. The process of speciation may fall within the purview of either, depending on the forces thought to drive it. Paleontology , evolutionary developmental biology , comparative genomics and genomic phylostratigraphy contribute most of the evidence for the patterns and processes that can be classified as macroevolution. An example of macroevolution is the appearance of feathers during the evolution of birds from one group of dinosaurs. Speciation is the evolutionary process by which new biological species arise. There are four modes of natural speciation, based on the extent to which speciating populations are geographically isolated from one another: allopatric , peripatric , parapatric , and sympatric .
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Comparison of allopatric , peripatric , parapatric and sympatric speciation. Stratigraphy , a branch of geology , studies rock layers and layering ( stratification ). It is primarily used in the study of sedimentary and layered volcanic rocks . Stratigraphy includes two related subfields: lithologic or lithostratigraphy and biologic stratigraphy or biostratigraphy . In anthropology and archaeology , homology is a type of analogy whereby two human beliefs, practices or artefacts are separated by time but share similarities due to genetic or historical connections. Specifically in anthropology, a homology is a structure that is shared through descent from a common ancestor. Taxonomy is the practice and science of classification . Divergent evolution occurs when two or more biological characteristics have a common evolutionary origin but have diverged over evolutionary time. This is also known as adaptation or adaptive evolution. These characters can be observable structures from different species or they can be molecular entities, such as genes or pathways. This is a kind of relationship observed in evolutionary biology .
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