Evolution

Evolution (also known as biological, genetic or organic evolution) is the change in the inherited traits of a population of organisms through successive generations.[1] Over time variants with particular heritable traits become more, or less, common. A trait is a particular characteristicanatomical, biochemical orbehaviouralthat is the result of geneenvironment interaction. One source of heritable variation is mutation, various types of which are passed on during the genetic recombination that happens at reproduction. Having occurred once, these changes can sometimes be passed on successfully to further generations, and may thus give rise to new variant traits in populations. Under certain circumstances, variation can also be increased by the transfer of genes between species,[2][3]and by the extremely rare, but significant, wholesale incorporation of genomes through endosymbiosis.[4][5] Two main processes cause variants to become more common or rarer in a population. One is natural selection, through which traits that aid reproduction become more common, while traits that hinder reproduction become rarer. Natural selection occurs because only a small proportion of individuals in each generation will reproduce, since resources are limited and organisms produce many more offspring than their environment can support. Over many generations, heritable variation in traits is filtered by natural selection and the beneficial changes are successively retained through differential survival and reproduction. This iterative process means that traits which are better suited to an organism's environment become more common. These adjustments are called adaptations.[6] However, not all change is adaptive. Another cause of evolution is genetic drift, which leads to random changes in how common traits are in a population. Genetic drift is most important when traits do not strongly influence survivalparticularly so in small populations, in which chance plays a disproportionate role in the frequency of traits passed on to the next generation.[7]
[8]

Genetic drift is important in the neutral theory of molecular evolution, and plays a role in

the molecular clocks that are used in phylogenetic studies. A notable result of evolution is speciation, in which a single ancestral species splits and diversifies into multiple distinct new populations that are new species. There are several ways in which this occurs. Ultimately, all living (and extinct) species are descended from a common ancestor via a long series of speciation events. These events stretch back in a diverse "tree of life" which has grown over the 3.5 billion years during which life has existed on Earth.[9][10][11]
[12]

This is visible in anatomical, genetic and other similarities between groups of

organisms, geographical distribution of related species, the fossil record and the recorded genetic changes in living organisms over many generations. Evolutionary biologists document the fact that evolution occurs, and also develop and test theories which explain its causes. The study of evolutionary biology began in the midnineteenth century, when research into the fossil record and the diversity of living organisms convinced most scientists that species changed over time.[13] The mechanism driving these changes remained unclear until the theory of natural selection was independently proposed by Charles Darwin and Alfred Wallace. In 1859, Darwin's seminal work On the Origin of Species brought the new theory of evolution by natural selection to a wide audience,[14] leading to the overwhelming acceptance of evolution among scientists.[15][16][17][18] In the 1930s, Darwinian natural selection became understood in combination with Mendelian inheritance, forming the modern evolutionary synthesis,[19] which connected the substrate of evolution (inherited genetics) and the mechanism of evolution (natural selection). This powerful explanatory and predictive theory has become the central organizing principle of modern biology, directing research and providing a unifying explanation for the history and diversity of life on Earth.[16][17][20] Evolution is applied and studied in fields as diverse as agriculture,anthropology, conservation biology, ecology, medicine, paleontology, philosophy, and psychology along with other specific topics in the previous listed fields.

Darwin's Theory of Evolution - The Premise Darwin's Theory of Evolution is the widely held notion that all life is related and has descended from a common ancestor: the birds and the bananas, the fishes and the flowers -- all related. Darwin's general theory presumes the development of life from non-life and stresses a purely naturalistic (undirected) "descent with modification". That is, complex creatures evolve from more simplistic ancestors naturally over time. In a nutshell, as random genetic mutations occur within an organism's genetic code, the beneficial mutations are preserved because they aid survival -- a process known as "natural selection." These beneficial mutations are passed on to the next generation. Over time, beneficial mutations accumulate and the result is an entirely different organism (not just a variation of the original, but an entirely different creature). Darwin's Theory of Evolution - Natural Selection While Darwin's Theory of Evolution is a relatively young archetype, the evolutionary worldview itself is as old as antiquity. Ancient Greek philosophers such as Anaximander postulated the development of life from non-life and the evolutionary descent of man from animal. Charles Darwin simply brought something new to the old philosophy -- a plausible mechanism called "natural selection." Natural selection acts to preserve and accumulate minor advantageous genetic mutations. Suppose a member of a species developed a functional advantage (it grew wings and learned to fly). Its offspring would inherit that advantage and pass it on to their offspring. The inferior (disadvantaged) members of the same species would gradually die out, leaving only the superior (advantaged) members of the species. Natural selection is the preservation of a functional advantage that enables a species to compete better in the wild. Natural selection is the naturalistic equivalent to domestic breeding. Over the centuries, human

breeders have produced dramatic changes in domestic animal populations by selecting individuals to breed. Breeders eliminate undesirable traits gradually over time. Similarly, natural selection eliminates inferior species gradually over time. Darwin's Theory of Evolution - Slowly But Surely... Darwin's Theory of Evolution is a slow gradual process. Darwin wrote, "Natural selection acts only by taking advantage of slight successive variations; she can never take a great and sudden leap, but must advance by short and sure, though slow steps." [1] Thus, Darwin conceded that, "If it could be demonstrated that any complex organ existed, which could not possibly have been formed by numerous, successive, slight modifications, my theory would absolutely break down." [2] Such a complex organ would be known as an "irreducibly complex system". An irreducibly complex system is one composed of multiple parts, all of which are necessary for the system to function. If even one part is missing, the entire system will fail to function. Every individual part is integral. [3] Thus, such a system could not have evolved slowly, piece by piece. The common mousetrap is an everyday non-biological example of irreducible complexity. It is composed of five basic parts: a catch (to hold the bait), a powerful spring, a thin rod called "the hammer," a holding bar to secure the hammer in place, and a platform to mount the trap. If any one of these parts is missing, the mechanism will not work. Each individual part is integral. The mousetrap is irreducibly complex. [4] Darwin's Theory of Evolution - A Theory In Crisis Darwin's Theory of Evolution is a theory in crisis in light of the tremendous advances we've made in molecular biology, biochemistry and genetics over the past fifty years. We now know that there are in fact tens of thousands of irreducibly complex systems on the cellular level. Specified complexity pervades the microscopic biological world. Molecular biologist Michael Denton wrote, "Although the tiniest bacterial cells are incredibly small, weighing less than 10-12 grams, each is in effect a veritable micro-miniaturized factory containing thousands of exquisitely designed pieces of intricate molecular machinery, made up altogether of one hundred thousand million atoms, far more complicated than any machinery built by man and absolutely without parallel in the nonliving world." [5] And we don't need a microscope to observe irreducible complexity. The eye, the ear and the heart are all examples of irreducible complexity, though they were not recognized as such in Darwin's day. Nevertheless, Darwin confessed, "To suppose that the eye with all its inimitable contrivances for adjusting the focus to different distances, for admitting different amounts of light, and for the correction of spherical and chromatic aberration, could have been formed by natural selection, seems, I freely confess, absurd in the highest degree." [6]