Support Aeon Donate now When researchers at Emory University in Atlanta trained mice to fear the smell of almonds by pairing it with electric shocksthey foundto their consternation, that both the children and grandchildren of these mice were spontaneously afraid of the same smell. That is not supposed to happen. Generations of schoolchildren have been taught that the inheritance of acquired characteristics is impossible.
Favourable variations are ones that increase chances for survival and procreation. Those advantageous variations are preserved and multiplied from generation to generation at the expense of less-advantageous ones.
This is the process known as natural selection. The outcome of the process is an organism that is well adapted to its environmentand evolution often occurs as a consequence. Natural selection, then, can be defined as the differential reproduction of alternative hereditary variants, determined by the fact that some variants increase the likelihood that the organisms having them will survive and reproduce more successfully than will organisms carrying alternative variants.
Selection may occur as a result of differences in survival, in fertility, in rate of development, in mating success, or in any other aspect of the life cycle.
All of these differences can be incorporated under the term differential reproduction because all result in natural selection to the extent that they affect the number of progeny an organism leaves. Darwin maintained that competition for limited resources results in the survival of the most-effective competitors.
Nevertheless, natural selection may occur not Characteristics of subsequent evolution as a result of competition but also as a result of some aspect of the physical environmentsuch as inclement weather. Moreover, natural selection would occur even if all the members of a population died at the same age, simply because some of them would have produced more offspring than others.
Natural selection is quantified by a measure called Darwinian fitness or relative fitness. Fitness in this sense is the relative probability that a hereditary characteristic will be reproduced; that is, the degree of fitness is a measure of the reproductive efficiency of the characteristic.
Biological evolution is the process of change and diversification of living things over time, and it affects all aspects of their lives— morphology form and structurephysiologybehaviour, and ecology.
Underlying these changes are changes in the hereditary materials. Evolution can be seen as a two-step process. First, hereditary variation takes place; second, selection is made of those genetic variants that will be passed on most effectively to the following generations.
Hereditary variation also entails two mechanisms—the spontaneous mutation of one variant into another and the sexual process that recombines those variants see recombination to form a multitude of variations. The variants that arise by mutation or recombination are not transmitted equally from one generation to another.
Some may appear more frequently because they are favourable to the organism; the frequency of others may be determined by accidents of chance, called genetic drift. The gene pool The gene pool is the sum total of all the genes and combinations of genes that occur in a population of organisms of the same species.
It can be described by citing the frequencies of the alternative genetic constitutions. Consider, for example, a particular gene which geneticists call a locussuch as the one determining the MN blood group s in humans.
One form of the gene codes for the M blood group, while the other form codes for the N blood group; different forms of the same gene are called allele s. The MN gene pool of a particular population is specified by giving the frequencies of the alleles M and N. Thus, in the United States the M allele occurs in people of European descent with a frequency of 0.
In other populations these frequencies are different; for instance, the frequency of the M allele is 0. The necessity of hereditary variation for evolutionary change to occur can be understood in terms of the gene pool.Racial characteristics such as height, iris color, and skin color are polygenic traits, that is, they are influenced by several genes.
Racial attributes map to sets of inheritable characteristics and are regulated by genes in different areas of the human genome. convergent evolution: The evolution of species from different taxonomic groups toward a similar form; the development of similar characteristics by taxonomically different organisms.
Evolution of the horse The evolutionary lineage of the horse is among the best-documented in all paleontology. The history of the horse family, Equidae, began during the Eocene Epoch, which lasted from about 56 million to million years ago. Essays in Natural History and Evolution: THE ESSAY in science is an art form as well as a means of communicating ideas.
All scientists publish their findings somewhere, but relatively few produce books or monographs. This article incorporates material from the Citizendium article "Evolution of cells", which is licensed under the Creative Commons Attribution-ShareAlike Unported License but not under the GFDL..
Further reading. Lerat E, Daubin V, Ochman H, Moran NA (). "Evolutionary Origins of Genomic Repertoires in Bacteria".
The formation and evolution of the Solar System began billion years ago with the gravitational collapse of a small part of a giant molecular cloud.