Natural selection definition
Natural selection is a process of adaptation by an organism to the changing environment by bringing selective changes to its genotype or genetic composition.
- Natural selection is one of the four primary mechanisms of evolution, along with mutation, genetic drift, and migration.
- Charles Darwin popularized the concept of natural selection during his studies on evolution.
- According to Darwin, natural selection is not an intentional process and is brought about by changes in the environment and the genotype of organisms.
- According to the mechanism of natural selection, the changes in the genotype of an organism that increase the chances of the organism to survive and procreate are preserved and passed down to the new generation.
- The less advantageous changes, however, are lost as the number of generations increases.
- This process of natural selection leads to the establishment of new niches, possibly resulting in speciation. Thus, natural selection is an essential mechanism of evolution.
- Natural selection might occur due to differences in survival, fertility, mating success, or in other aspects of the life cycle.
- No matter how small these changes are, as long as they are heritable, they might result in a natural selection over many generations.
- In this way, nature ‘selects’ organisms with particular beneficial traits resulting in reproductive advantage, causing evolutionary change.
- The concept of fitness is crucial while discussing natural selection. Fitness of an animal is not only defined by how long it survives, but also by its reproductive success.
- Thus, if an animal lives only half as long as the others, but has twice as many offsprings surviving till adulthood, the animal is considered more fit and thus, will be ‘selected’ by nature.
- Another mechanism that ensures natural selection is by competition where the more fit individuals can compete with the less fit for food, shelter, and other resources.
- As a result of such competition, the fewer fit individuals die out, leaving the more fit ones to survive and reproduce.
- Natural selection, however, is a prolonged process that takes many generations for the effects to be seen.
- It occurs in a natural population, resulting in a large biological diversity which might be random.
- The increase in diversity also causes an increase in heterozygous genotypes within a species.
- Some examples of natural selection include the selection of long-necked giraffes and the changes in the size and shape of beaks of birds according to their feeding habits.
Artificial selection definition
Artificial selection, also called selective breeding, is the process where humans identify desirable traits in animals and plants and use these traits to develop desirable phenotypic traits by breeding.
- Although the process of artificial selection uses the same mechanism as natural selection, artificial selection is a controlled process caused by humans, whereas natural selection occurs due to natural causes.
- The process of artificial selection is based on the studies done by Charles Darwin, where he concluded how selective breeding facilitates desirable changes over a period of time.
- Unlike natural selection, artificial selection doesn’t result in evolution or speciation.
- Artificial selection is a comparatively faster process where the effects are seen over a few generations.
- Domesticated animals and plants are often selected based on their desirable phenotypic traits to produce crossbred plants and animals.
- This selection is made by the farmers to bring higher productivity and better quality.
- Artificial selection in animals begins with purebred animals with a single breed and desirable traits, which are then bred with other purebred animals to develop and preserve superior qualities.
- In animals, artificial selection is brought about by inbreeding, linebreeding, or outcrossing.
- The hybrids formed after selective breeding tend to have a higher vigor, termed hybrid vigor. However, sometimes, these breeding might also result in degradation of quality.
- A similar process is applied for plant breeding where wild plants are domesticated into uniform and predictable agriculture.
- The same process is applied for plant breeding, where plants with houseful traits like higher production are bred to preserve these traits and even develop superior traits.
- Selective plant breeding has been used for thousands of years for agricultural purposes; nowadays, however, it is also used in research regarding transgenic plants that are homozygous for various genes.
- Even though the process of artificial selection is controlled, sometimes it might occur unintentionally during farming that might produce either desirable or undesirable effects.
- The advantages related to artificial breeding include higher productivity and healthier offsprings, along with a more convenient and faster analysis of offsprings.
- There are, however, some disadvantages of artificial selection as it cannot be performed on an entire population at once and also the processes need to be performed under lab conditions or in a greenhouse.
- The artificial selection also decreases the genetic diversity in a population as most fit species are bred with each other, increasing the homozygous genotypes.
- Some examples of artificial selection include dog breeding to produce new breeds of dogs and cross-breeding in cash crops like wheat and rice.
Key Differences (Natural selection vs Artificial selection)
Basis for Comparison
|Definition||Natural selection is a process of adaptation by an organism to the changing environment by bringing selective changes to its genotype or genetic composition.||Artificial selection, also called selective breeding, is the process where humans identify desirable traits in animals and plants and use these traits to develop desirable phenotypic traits by breeding.|
|Process||Natural selection is a natural process.||Artificial selection is an artificial or human-made process.|
|Occurs in||Natural selection takes place in natural populations within natural conditions.||Artificial selection takes place in domesticated populations put together by humans.|
|Chances of survival||The chances of survival of a fit organism increase as a result of natural selection.||The chance of survival of an organism might be at risk if not performed correctly.|
|Rate||Natural selection is a slow process that completes after many generations.||Artificial selection is a faster process that completes within days or weeks with more apparent effects.|
|Controlled by||Natural selection is not as controlled as artificial selection as natural processes control it.||Artificial selection can be more controlled as humans control it.|
|Performed on||Natural selection might occur on all organisms living on the earth.||Artificial selection can be selective and can be performed on selected groups of animals and plants.|
|Traits||Natural selection is based on the adaptive characteristics of animals.||Artificial selection is based on the desirable characters selected by humans.|
|Only beneficial or favorable traits are inherited over the successive generations by natural selection.||Artificial selection only allows the selected traits to be passed through successive generations.|
|Affects||Natural selection affects the entire population of a species.||Artificial selection only affects the selected individuals.|
|Diversity||Natural selection results in a large amount of biological diversity.||Artificial selection only brings desirable changes and desirable traits and brings a decrease in genetic diversity.|
|Evolution||Natural selection facilitates speciation and evolution over many generations.||Artificial selection doesn’t facilitate evolution.|
|Scale||Natural selection exerts on a wide-scale on the natural environment.||Artificial selection exerts only on selected individuals that are economically important.|
|Hybrid vigor||Hybrid vigor is seen in offsprings after natural selection.||Hybrid vigor is lost during artificial selection due to the preservation of desired traits.|
|Effort||Natural selection is a natural process, so no human effort is required.||The artificial selection might be labor-intensive and expensive.|
|Genotype||After natural selection, the proportion of heterozygous genotype becomes high.||After artificial selection, the proportion of homozygous genotype becomes high.|
|Examples||Some examples of natural selection include the selection of long-necked giraffes and the changes in the size and shape of beaks of birds according to their feeding habits.||Some examples of artificial selection include dog breeding to produce new breeds of dogs and cross-breeding in cash crops like wheat and rice.|
Examples of natural selection
Selection of long-necked giraffes
- The selection of long-necked giraffes from the short-necked giraffes is a classic example of natural selection.
- It is assumed that many generations ago, both long-necked and short-necked giraffes existed on earth.
- However, as time progressed, the food on the land started to be scarce. Thus, these giraffes had to feed on leaves present on the top of tall trees.
- The long-necked giraffes could easily reach these leaves, whereas the short-necked giraffes couldn’t. As a result, the short-necked slowly became extinct due to the lack of food, but the long-necked giraffes survived.
- In this case, the lack of grasses is an environmental change that causes the selection of more ‘fit’ individuals and the extinction of less ‘fit’ individuals.
Sexual selection in peacocks
- In peacocks, competition occurs between many male peacocks to find an appropriate mate.
- The male peacocks exhibit natural selection in the form of long colorful and attractive tails that attract female peacocks.
- Thus, males with dazzling tails are successful in attracting females even if it has no resemblance in the ability of the male to collect food or reproduce.
- Thus, the males with more attractive tails are naturally selected over the ones with smaller tails.
- A similar mechanism is also seen in other birds like ducks and tropical birds where the males are more decorated than the females.
Examples of artificial selection
- Dog breeding is a common phenomenon, and it is assumed that the purebred dogs found today have been artificially selected since 14,000 years.
- The breeding in ancient times was done primarily to obtain a friendlier, faster, and useful version of the existing ancestors.
- These dogs were made better to increase their chances of the hunt and the ability to protect its human owner.
- Over time, as humans began to keep dogs as pets, the purpose changed to guard the house and shock intruders, and thus dogs like greyhound were interbred to obtain strong and active breeds of dogs.
- Nowadays, dogs are kept at home and act as companions for most people. As a result, the purpose of artificial breeding changed to produce friendlier and cuter dogs like poodles and bulldogs.
Selection of cash crops
- Artificial selection of crops has been going on for a long period of time.
- It is assumed that the ancestor of all wheat species present today is the Triticum monococcumor einkorn wheat first cultivated in Asia about 40,000 years ago.
- This plant was then inbred or crossbred with different other species to increase production and species of wheat.
- Currently, different species of wheat are used for different purposes like wheat used from beer production is different than that used for pasta and other noodles.
- These species are produced by selecting certain species that are fit for their different purposes.
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