Evolution, Evolution

These traits vary within populations, with organisms showing heritable differences (variation) in their traits. Evolution itself is the product of two opposing forces: processes that constantly introduce variation, and processes that make variants become more common or rare. New variation arises in two main ways: either from mutations in genes, or from the transfer of genes between populations and between species. In species that reproduce sexually, new combinations of genes are also produced by genetic recombination, which can increase variation between organisms.

Darwin's landmark work On the Origin of Species of 1859 brought the new theories of evolution by natural selection to a wide audience. . Related earlier ideas were acknowledged in Darwin's work soon led to overwhelming acceptance of evolution among scientists.

Another interesting but unsolved question in genetics is if epigenetics is important in evolution, this is where heritable changes occur in organisms without there being any changes to the sequences of their genes.

For example, all of the moths of the same species living in an isolated forest represent a population. A single gene in this population may have several alternate forms, which account for variations between the phenotypes of the organisms. An example might be a gene for coloration in moths that has two alleles: black and white. A gene pool is the complete set of alleles for a gene in a single population; the allele frequency measures the fraction of the gene pool comprised of a single allele (for example, what fraction of moth coloration genes are the black allele). Evolution occurs when there are changes in the frequencies of alleles within a population of interbreeding organisms; for example, the allele for black color in a population of moths becoming more common.

These adaptations increase fitness by aiding activities such as finding food, avoiding predators or attracting mates. Organisms can also respond to selection by co-operating with each other, usually by aiding their relatives or engaging in mutually beneficial symbiosis. In the longer term, evolution produces new species through splitting ancestral populations of organisms into new groups that cannot or will not interbreed.

For instance, a large amount of variation among individuals allows a species to rapidly adapt to new habitats, lessening the chance of it going extinct, while a wide geographic range increases the chance of speciation, by making it more likely that part of the population will become isolated. In this sense, microevolution and macroevolution might involve selection at different levels - with microevolution acting on genes and organisms, versus macroevolutionary processes acting on entire species and affecting the rate of speciation and extinction.

For example, the adaptation of horses' teeth to the grinding of grass, or the ability of horses to run fast and escape predators. By using the term adaptation for the evolutionary process, and adaptive trait for the product (the bodily part or function), the two senses of the word may be distinguished. Adaptations are produced by natural selection.

Dobzhansky T. 1968. On some fundamental concepts of evolutionary biology.

This is the result of a single ancestral structure being adapted to function in different ways. The bones within bat wings, for example, are structurally similar to both human hands and seal flippers, due to the common descent of these structures from an ancestor that also had five digits at the end of each forelimb. Other idiosyncratic anatomical features, such as bones in the wrist of the panda being formed into a false "thumb," indicate that an organism's evolutionary lineage can limit what adaptations are possible.

Here, the evolution of one species causes adaptations in a second species. These changes in the second species then, in turn, cause new adaptations in the first species. This cycle of selection and response is called co-evolution.

In this predator-prey pair, an evolutionary arms race has produced high levels of toxin in the newt and correspondingly high levels of resistance in the snake.

This is similar to peripatric speciation in that a small population enters a new habitat, but differs in that there is no physical separation between these two populations. Instead, speciation results from the evolution of mechanisms that reduce gene flow between the two populations.

As a result, the periods of stasis in the fossil record correspond to the parental population, and the organisms undergoing speciation and rapid evolution are found in small populations or geographically restricted habitats, and therefore rarely being preserved as fossils.

That variation is the main fuel used by natural selection to shape the wide variety of adaptive traits observed in organic life. Even though Hugo de Vries and other early geneticists were very critical of the theory of evolution, their rediscovery of and subsequent work on genetics eventually provided a solid basis on which the theory of evolution stood even more convincingly than when it was originally proposed. Quammen, D. (2006).

Haldane, Sewall Wright, and particularly Ronald Fisher, who set the foundations for the establishment of the field of population genetics. The end result was a combination of evolution by natural selection and Mendelian inheritance, the modern evolutionary synthesis.

In the 21st century, current research in evolutionary biology deals with several areas where the modern evolutionary synthesis may need modification or extension, such as assessing the relative importance of various ideas on the unit of selection and evolvability and how to fully incorporate the findings of evolutionary developmental biology.

Nowadays, the fact that organisms evolve is uncontested in the scientific literature and the modern evolutionary synthesis is widely accepted by scientists.

Source: Wikipedia > Evolution