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Evolutionary rate
Evolutionary rate is the the slow change in a lineage across many generations through the accumulation of mutations in heritable DNA[1]. The rate can be measured through changes in phenotype or genotype. The evolutionary rate is used to track divergences in phylogenetic tree where a new species emerges from the parent lineage.
Methods of Analysis
A species diverges from another when the chromosomal DNA does not share enough homology with the ancestral line to yield fertile offspring capable of meiosis. Typically, several genes from many individuals are sequenced and compared for homology and consensus sequences. The rate is measured in sequence changes across multiple genes per base pair per year of divergence between species[2]. However, not all mutations occur at the same rate; therefore, the relative frequencies of transversions and transitions must be considered. Genes undergo mutations at varying rates depending on the structure of the gene or conservation. Many genes are needed in order to compensate for the variations of mutation rates.
Factors that influence Evolutionary Rate
A population living without selection factors will not exhibit the purging or integration of adaptive traits. During this period, as seen with crocodiles, the organism is properly suited to the environment. New alleles and traits would evolve spontaneously at a predictable pace based on calculated molecular mutation rates in genes. However, a population under stress would undergo selection for new traits that actively benefit the organism, while the less fit organisms are weened from the population and the species. A dramatic climate change, the introduction of a new disease or increased competition for food are among many factors that drive the rpocess of natural selection. during this period, the evolutionary rate increases as the population shrinks, and alleles are actively selected out of the gene pool.