Adaptation and Natural Selection: Overview
Adaptation: Adaptation, in biology, process by which an animal or plant species becomes fitted to its environment; it is the result of natural selection's acting upon Even the simpler organisms must be adapted in a great variety of ways: in their when it was used to indicate a relation between design and function or how. Natural selection helps species adapt to change across generations but does not help living beings cope with fast environmental change. Charles Darwin's voyage on the HMS Beagle and his ideas about evolution and which included stops in South America, Australia, and the southern tip of Africa. explain how each finch population had acquired adaptations, or features that . obvious if we flipped the dominance relationships (making black dominant to.
This mechanism was elegant and logical, and it explained how populations could evolve undergo descent with modification in such a way that they became better suited to their environments over time. Darwin's concept of natural selection was based on several key observations: Traits are often heritable.
In living organisms, many characteristics are inherited, or passed from parent to offspring. Darwin knew this was the case, even though he did not know that traits were inherited via genes. More offspring are produced than can survive. Organisms are capable of producing more offspring than their environments can support. Thus, there is competition for limited resources in each generation.
Offspring vary in their heritable traits. The offspring in any generation will be slightly different from one another in their traits color, size, shape, etc. Based on these simple observations, Darwin concluded the following: In a population, some individuals will have inherited traits that help them survive and reproduce given the conditions of the environment, such as the predators and food sources present.
The individuals with the helpful traits will leave more offspring in the next generation than their peers, since the traits make them more effective at surviving and reproducing. Because the helpful traits are heritable, and because organisms with these traits leave more offspring, the traits will tend to become more common present in a larger fraction of the population in the next generation.
Over generations, the population will become adapted to its environment as individuals with traits helpful in that environment have consistently greater reproductive success than their peers. Darwin's model of evolution by natural selection allowed him to explain the patterns he had seen during his travels.
If groups of finches had been isolated on separate islands for many generations, however, each group would have been exposed to a different environment in which different heritable traits might have been favored, such as different sizes and shapes of beaks for using different food sources. These factors could have led to the formation of distinct species on each island. If one island had plants that made large seeds, but few other food sources, birds with larger, tougher beaks than average might have been more likely to survive and reproduce there.
That's because the big-beaked birds would have been more able to crack open the seeds and eat the contents, and thus less likely to starve. If another island had many insect species but few other food sources, birds with thinner, sharper beaks than average might have been more likely to survive and reproduce there.
That's because the sharp-beaked birds would have been better able to catch insects as prey, and thus less likely to starve. Over many generations, these patterns of different survival and reproduction based on beak shape a heritable trait could have caused a shift in the average beak shape of each population.
Specifically, the population on the first island might have shifted towards a larger, tougher beak on average, while the population on the second island might have shifted towards a thinner, sharper beak on average. Eventually, the two populations of finches might have looked different enough from one another due to this change, and, potentially, other similar changes to be classified as different species.
How natural selection can work To make natural selection more concrete, let's consider a simplified, hypothetical example. In this example, a group of mice with heritable variation in fur color black vs.
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This environment features hawks, which like to eat mice and can see the tan ones more easily than the black ones against the black rock. Because the hawks can see and catch the tan mice more easily, a relatively large fraction of the tan mice are eaten, while a much smaller fraction of the black mice are eaten.
If we look at the ratio of black mice to tan mice in the surviving "not-eaten" group, it will be higher than in the starting population. Hawk outline traced from " Black and white line art drawing of Swainson hawk bird in flight ," by Kerris Paul public domain.
So, the increased fraction of black mice in the surviving group means an increased fraction of black baby mice in the next generation. After several generations of selection, the population might be made up almost entirely of black mice. This change in the heritable features of the population is an example of evolution.
However, if the question of inheritance pattern is bothering you, here is one way you can think about it: If we see only black and tan mice in the population, then a simple explanation is that the fur color trait is controlled by a single gene whose two alleles have a complete dominance relationship. Let's say, for the sake of argument, that tan is dominant T and black is recessive t.
This means that a tan mouse could be either Tt or TT, while a black mouse must be tt. In the extreme case where all tan mice are eaten by predators before reproductive age, the only mice who will leave any offspring are black tt mice, who will mate with one another and produce more black tt offspring.
In reality, selection probably would not be that strong. Some tan mice would make it to mating season, and when they mated with the black mice, some tan baby mice would be born along with black baby mice. However, the more tan mice that got siphoned out of the gene pool by the predators, the higher the fraction of black-furred baby mice we'd expect to see in the next generation.
The genetics would be a little less obvious if we flipped the dominance relationships making black dominant to tanbut the same principle would hold: You can learn more evolution at the level of alleles and genes in the population genetics tutorial. Key points about natural selection When I was first learning about natural selection, I had some questions and misconceptions!
Here are explanations about some potentially confusing points, which may help you get a better sense of how, when, and why natural selection takes place. Natural selection depends on the environment Natural selection doesn't favor traits that are somehow inherently superior. Instead, it favors traits that are beneficial that is, help an organism survive and reproduce more effectively than its peers in a specific environment. Traits that are helpful in one environment might actually be harmful in another.
Instead, they become more common because they have a heritable feature that makes them better able to survive and reproduce in a specific setting, one that happens to include black rocks.
In a setting with light-colored rocks, the helpful and harmful traits would be reversed. Natural selection acts on existing heritable variation Natural selection needs some starting material, and that starting material is heritable variation. For natural selection to act on a feature, there must already be variation differences among individuals for that feature. Also, the differences have to be heritable, determined by the organisms' genes.
If all the mice had been tan, the population would have had no way to adapt to its new environment by natural selection and might instead have been wiped out.
What if there had been non-heritable variation e. This might have affected the survival of the individuals, but it wouldn't have changed the composition of the population over generations because the babies of the dyed tan mice would have inherited the tan-mouse gene variants present in their parents, not black-mouse ones.
Heritable variation comes from random mutations The original source of the new gene variants that produce new heritable traits, such as fur colors, is random mutation changes in DNA sequence. Random mutations that are passed on to offspring typically occur in the germline, or sperm and egg cell lineage, of organisms. Sexual reproduction "mixes and matches" gene variants to make more variation. That is, a mouse can't intentionally mutate to make itself or its offspring a different color. Instead, if there by chance happens to be a mutation that changes mouse fur color, the variation produced by that mutation may be acted on by natural selection.
Natural selection and the evolution of species Let's take a step back and consider how natural selection fits in with Darwin's broader vision of evolution, one in which all living things share a common ancestor and are descended from that ancestor in a huge, branching tree. What is happening at each of those branch points? In the example of Darwin's finches, we saw that groups in a single population may become isolated from one another by geographical barriers, such as ocean surrounding islands, or by other mechanisms.
Once isolated, the groups can no longer interbreed and are exposed to different environments. In each environment, natural selection is likely to favor different traits and other evolutionary forces, such as random drift, may also operate separately on the groups. Over many generations, differences in heritable traits can accumulate between the groups, to the extent that they are considered separate species.
Based on various lines of evidencescientists think that this type of process has repeated many, many times during the history of life on Earth. Evolution by natural selection and other mechanisms underlies the incredible diversity of present-day life forms, and the action of natural selection can explain the fit between present-day organisms and their environments.
Download the original article for free at http: Influences on Darwin - Advanced. In CK biology advanced concepts. The voyage of the Beagle. In the human body the large bulging muscles of an individual engaged in heavy labour are a good example of cellular… The word adaptation does not stem from its current usage in evolutionary biology but rather dates back to the early 17th century, when it was used to indicate a relation between design and function or how something fits into something else.
In biology this general idea has been coopted so that adaptation has three meanings. First, in a physiological sense, an animal or plant can adapt by adjusting to its immediate environment—for instance, by changing its temperature or metabolism with an increase in altitude.
Second, and more commonly, the word adaptation refers either to the process of becoming adapted or to the features of organisms that promote reproductive success relative to other possible features. Here the process of adaptation is driven by genetic variations among individuals that become adapted to—that is, have greater success in—a specific environmental context. A classic example is shown by the melanistic dark phenotype of the peppered moth Biston betulariawhich increased in numbers in Britain following the Industrial Revolution as dark-coloured moths appeared cryptic against soot-darkened trees and escaped predation by birds.
The process of adaptation occurs through an eventual change in the gene frequency relative to advantages conferred by a particular characteristic, as with the coloration of wings in the moths. Against the background of a lichen-covered oak tree, a darkly pigmented peppered moth Biston betularia stands out, while the light gray moth left remains inconspicuous. From the experiments of Dr. Kettlewell, University of Oxford; photographs by John S. Haywood The third and more popular view of adaptation is in regard to the form of a feature that has evolved by natural selection for a specific function.
Examples include the long necks of giraffes for feeding in the tops of trees, the streamlined bodies of aquatic fish and mammals, the light bones of flying birds and mammals, and the long daggerlike canine teeth of carnivores.
All biologists agree that organismal traits commonly reflect adaptations. However, much disagreement has arisen over the role of history and constraint in the appearance of traits as well as the best methodology for showing that a trait is truly an adaptation.
A trait may be a function of history rather than adaptation. The ancestors of giant pandas and all closely related species, such as black bearsraccoonsand red pandasalso have sesamoid bones, though the latter species do not feed on bamboo or use the bone for feeding behaviour.
Therefore, this bone is not an adaptation for bamboo feeding.