Genetic variation is a term used to describe the variation in the DNA sequence in each of our genomes. Genetic variation is what makes us all unique, whether in terms of hair colour, skin colour or even the shape of our faces. The fruit fly, also known as Drosophila melanogaster , has the longest history in genetics and research out of all the model organisms.
Inheritance is the process by which genetic information is passed on from parent to child. This is why members of the same family tend to have similar characteristics. Selective breeding involves selecting parents that have characteristics of interest in the hope that their offspring inherit those desirable characteristics. If you have any other comments or suggestions, please let us know at comment yourgenome. Can you spare minutes to tell us what you think of this website?
Open survey. In: Facts Society and Behaviour. The theory of evolution is based on the idea that all species are related and gradually change over time. Evolution relies on there being genetic variation in a population which affects the physical characteristics phenotype of an organism. Hilaire against Cuvier Gayon ; entry on evolutionary thought before Darwin , 4. Darwin was, as a consequence, viewed as endorsing rejected science by leading figures of French science.
On the other hand, the Comtean three stages view of history, with its claim about the historical transcendence of speculative and metaphysical periods of science by a final period of experimental science governed by determinate laws, placed Darwinism in a metaphysical phase of speculative nature philosophy, as captured in the above quotation from Claude Bernard.
Richards , , ; Gliboff , ; Mullen More than any other individual, Haeckel made Darwinismus a major player in the polarized political and religious disputes of Bismarckian Germany R.
Richards Through his polemical writings, such as the Natural History of Creation , Anthropogeny , and Riddle of the Universe —99 , Haeckel advocated a materialist monism in the name of Darwin, and used this as a stick with which to beat traditional religion.
Beginning in with a partial translation by Ma Junwu — , a Chinese scientist, trained in chemistry and metallurgy in Japan and Germany, the early chapters of the Origin itself were made available to a Chinese audience. This group can usually be distinguished from lay interpreters who may not have made distinctions between the views of Lamarck, Chambers, Schelling, Spencer, and Darwin on the historical development of life.
But this only gives a crude instrument of analysis. The case of Ernst Haeckel displays this imprecision. He was a leading professor of zoology at an important German university Jena , and he formed a generation of scientific workers in embryology and natural history who had major impact on the history of the life sciences. Richards chp. Darwin himself feared a similar reception, and he recognized the substantial challenge facing him in convincing this group and the larger community of scientific specialists with which he interacted and corresponded widely.
With this group he was only partially successful. Of central importance in analyzing this complex professional reception was the role assigned to normal individual variation and its causes. Darwin, however, left the specific causes of this variation unspecified beyond some effect of the environment on the sexual organs. As critics focused their attacks on the claim that such micro-differences between individuals could be accumulated over time without natural limits, Darwin began a series of modifications and revisions of the theory through a back and forth dialogue with his critics that can be followed by revisions to the text of the Origin.
In the fourth edition of , for example, Darwin inserted the claim that the continuous gradualism illustrated by his branching diagram was misleading, and that transformative change does not necessarily go on continuously. This change-stasis-change model presumably allowed variation to stabilize for a period of time around a mean value from which additional change could then resume.
Such a model would, however, presumably require even more time for its working than the multi-millions of years assumed in the original presentation of the theory. Using an argument previously raised in the s by Charles Lyell against Lamarck, Fleeming Jenkin cited empirical evidence from domestic breeding that suggested a distinct limitation on the degree of variation, and denied that selection upon this could be taken to the extent assumed by Darwin Fleeming Jenkin ; Hoquet Using a loosely mathematical argument, Fleeming Jenkin argued that the effects of intercrossing would continuously swamp deviations from the mean values of characters and result in a tendency of the variation in a population to return to mean values over time.
The time difficulties were only resolved in the twentieth-century with the discovery of radioactivity. Although this theory had been formulated independently of the Jenkin review Olby , in effect it functioned as his reply to it.
It also explained how use-disuse inheritance, a theory which Darwin never abandoned, could work. The pangenesis theory, although not specifically referred to, seems to be behind an important distinction he inserted into the fifth edition of the Origin of where he made a direct reply to the criticisms of Jenkin. The latter were now the form of variation to be given primary evolutionary significance, and presumably this was more likely to be transmitted to the offspring, although details are left unclear.
In this form it presumably could be maintained in a population against the tendency to swamping by intercrossing. The debates over variation placed Darwinism in a defensive posture that forced its supporters into major revisions in the Darwinian research program Gayon ; Vorzimmer Darwin had retained his own conclusions on human evolution quietly in the background while the defense of his general theory was conducted by advocates as diverse as Thomas Henry Huxley —95 in England, Asa Gray —88 in the United States, and Ernst Haeckel — in Germany.
At this time he also sent to several correspondents a questionnaire asking for information on human emotional expression. This was expanded into a two volume work by the time it was sent to the printer in June of By this date he had also pulled out a separate section from the Variation manuscript that was to become the Expression of the Emotions in Man and the Animals ,published in Only Haeckel had drawn out a more general reductive conception of humanity from evolutionary theory and he had not ventured into the specific issues of ethics, social organization, the origins of human races, and the relation of human mental properties to those of animals, all of which are dealt with in the Descent.
The more fundamental opposition was due to the denial of distinctions, other than those of degree, between fundamental human properties and those of animals. As a consequence, the favorable readings that many influential religious thinkers—John Henry Newman — is a good example—had given to the original Origin , disappeared. Most striking in comparing the Origin to the Descent was the strong emphasis on the workings of the secondary process of sexual selection in the animal kingdom E.
Richards ; R. Sexual selection—the selection of females by males or vice versa for breeding purposes—had given a general statement of this principle in chapter four of the Origin , but this played a minor role in the original argument, and its importance was denied by contemporaries like A.
Darwin now developed this secondary form of selection in extensive detail as a factor in evolution that could even work against ordinary natural selection. Sexual selection could now be marshaled to explain both sexual dimorphism and also those character and properties of organisms—elaborate feeding organs, bright colors on fish and birds, and seemingly maladaptive structures such as the great horn on the Rhinoceros beetle—, that might appear to be anomalous outcomes of ordinary natural selection working to the optimal survival of organisms in nature.
In a dramatic extension of this principle to human beings, the combination of natural and sexual selection is used to explain the origins of the human beings from simian ancestors. It also explains the sexual dimorphism displayed by human beings, and is the main factor accounting for the origin of human races.
In this closing subsection the author will focus exclusively on one important aspect of this broader social impact of the Descent , the Darwinian treatment of ethics. This will be examined within its specific Victorian context, rather than in light of more recent discussions of altruism within contemporary sociobiology that may owe some filiation with these Darwinian discussion see entries on morality and evolutionary biology and biological altruism.
As can be seen from the letter to Asa Gray of March Burkhardt et al. The closest connections might be drawn with certain aspects of contemporary virtue ethics and some aspects of Natural Law theory, although there are many specific differences that prevent assimilation to these traditions as well Sloan Richards , , ,.
Traditional moral sense theory linked ethical behavior to an innate property or instinct that was considered universal in human beings, even though it required education and cultivation to reach its highest expression see moral sentimentalism in this encyclopedia.
It also did not involve the rational calculation of advantage by the individual prior to action. The moral sense, for Darwin, was derived by biological descent from animal instinct, and particularly from the social instincts developed by natural selection.
Natural and sexual selection then shaped these ethical instincts in ways that favored group survival rather than immediate individual benefit Descent vol. Human ethical behavior is therefore grounded in a natural property, and ethical action can occur without moral calculus or rational deliberation.
The innate moral sense is his explanation for self-sacrifice and other altruistic acts that cannot be attributed to individual self-survival vol. Humans can be. Descent vol. When moral conflict occurs, this is generally attributed to a conflict of instincts, with the stronger of two conflicting instincts favored by natural selection insofar as it favors group benefit Descent vol.
For some moral philosophers, Darwin had simply reduced ethics to a property subject to the relativizing tendencies of natural selection Farber chp. Receiving its most influential expression in G. The historiography adopted in this article rejects a simple linear story of the development of Darwinian theory as a history of increasingly true theories leading to a present consensus.
More general philosophical issues associated with evolutionary theory—those surrounding natural teleology, ethics, the relation of evolutionary naturalism to the claims of religious traditions, the implications for the relation of human beings to the rest of the organic world—continue as issues of scholarly inquiry.
The author wishes to acknowledge the valuable comments on this article by David Depew, M. Hodge, Robert Richards, and Xiaoxing Jin. Katherine Tillman, and the anonymous reviewers for the Stanford Encyclopedia of Philosophy. I am particularly indebted to my student, Mr.
Xiaoxing Jin, for information contained in his substantial doctoral work and subsequent research on the reception of Darwinism into China. Responsibility for all interpretations is my own. Darwinian Evolution 2. The Concept of Natural Selection 2. In later generations, more genetic changes occurred, moving the nose farther back on the head. Other body parts of early whales also changed. Front legs became flippers. Back legs disappeared. Their bodies became more streamlined, and they developed tail flukes to better propel themselves through water.
Darwin also described a form of natural selection that depends on an organism's success at attracting a mate — a process known as sexual selection. The colorful plumage of peacocks and the antlers of male deer are both examples of traits that evolved under this type of selection.
But Darwin wasn't the first or only scientist to develop a theory of evolution. Around the same time as Darwin, British biologist Alfred Russel Wallace independently came up with the theory of evolution by natural selection, while French biologist Jean-Baptiste Lamarck proposed that an organism could pass on traits to its offspring, though he was wrong about some of the details.
Like Darwin, Lamarck believed that organisms adapted to their environments and passed on those adaptations. He thought organisms did this by changing their behavior and, therefore, their bodies — like an athlete working out and getting buff — and that those changes were passed on to offspring.
For example, Lamarck thought that giraffes originally had shorter necks but that, as trees around them grew taller, they stretched their necks to reach the tasty leaves and their offspring gradually evolved longer and longer necks. Lamarck also believed that life was somehow driven to evolve through the generations from simple to more complex forms, according to Understanding Evolution , an educational resource from the University of California Museum of Paleontology.
Though Darwin wasn't sure of the mechanism by which traits were passed on, he did not believe that evolution necessarily moved toward greater complexity, according to Understanding Evolution; rather, he believed that complexity arose through natural selection. A Darwinian view of giraffe evolution, according to Quanta , would be that giraffes had natural variation in their neck lengths, and that those with longer necks were better able to survive and reproduce in environments full of tall trees, so that subsequent generations had more and more long-necked giraffes.
The main difference between the Lamarckian and Darwinian ideas of giraffe evolution is that there's nothing in theDarwinian explanation about giraffes stretching their necks and passing on an acquired characteristic. Darwin didn't know anything about genetics, Pobiner said. That came later, with the discovery of how genes encode different biological or behavioral traits, and how genes are passed down from parents to offspring.
The incorporation of genetics into Darwin's theory is known as "modern evolutionary synthesis. The physical and behavioral changes that make natural selection possible happen at the level of DNA and genes within the gametes, the sperm or egg cells through which parents pass on genetic material to their offspring.
Such changes are called mutations. Mutations can be caused by random errors in DNA replication or repair, or by chemical or radiation damage. Usually, mutations are either harmful or neutral, but in rare instances, a mutation might prove beneficial to the organism. If so, it will become more prevalent in the next generation and spread throughout the population. Skip to content. Image Young Charles Darwin Charles Darwin is more famous than his contemporary Alfred Russel Wallace who also developed the theory of evolution by natural selection.
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