Table of Contents
- Natural selection definition
- Artificial selection definition
- Key Differences (Natural selection vs Artificial selection)
- Examples of natural selection
- Examples of artificial selection
- References and Sources
Natural selection definition
- Natural selection is a process of adaptation by an organism to the changing environment through selective changes in its genotype or genetic composition.
- It is one of the four primary mechanisms of evolution, alongside mutation, genetic drift, and migration.
- The concept of natural selection was popularized by Charles Darwin during his studies on evolution.
- According to Darwin, natural selection is not an intentional process but is driven by changes in the environment and the genotype of organisms.
- The mechanism of natural selection preserves genetic changes that increase an organism's chances of survival and reproduction, passing them down to future generations.
- Genetic changes that are less advantageous tend to disappear over multiple generations.
- This process can lead to the formation of new niches and potentially result in speciation, making natural selection an essential mechanism of evolution.
- Natural selection can occur due to differences in survival, fertility, mating success, or other aspects of the life cycle.
- Even small heritable changes can lead to natural selection if passed on over many generations.
- Through this process, nature "selects" organisms with beneficial traits, leading to a reproductive advantage and evolutionary change.
- The concept of fitness is central to natural selection and is defined not only by an organism’s lifespan but also by its reproductive success.
- An animal that lives half as long but has twice as many surviving offspring is considered more fit and thus more likely to be "selected" by nature.
- Competition also drives natural selection, where more fit individuals outcompete less fit ones for resources such as food and shelter.
- This competition leads to the survival and reproduction of the more fit individuals while the less fit may die out.
- Natural selection is a gradual process that takes many generations to show noticeable effects.
- It occurs within natural populations and contributes to biological diversity, which may be random.
- This increased diversity results in a rise in heterozygous genotypes within a species.
- Examples of natural selection include the evolution of long-necked giraffes and the adaptation of birds' beak size and shape according to their feeding habits.
Artificial selection definition
- Artificial selection, also known as selective breeding, is the process in which humans identify desirable traits in animals and plants and breed them to develop preferred phenotypic traits.
- While it uses the same basic mechanism as natural selection, artificial selection is a human-controlled process, unlike natural selection, which occurs due to natural causes.
- The concept of artificial selection is based on studies by Charles Darwin, who showed how selective breeding can bring about desirable changes over time.
- Unlike natural selection, artificial selection does not lead to evolution or speciation.
- Artificial selection is a faster process, with noticeable effects appearing within a few generations.
- Domesticated animals and plants are chosen for breeding based on desirable phenotypic traits to create crossbred species with improved qualities.
- Farmers select organisms to increase productivity and improve quality.
- In animals, artificial selection begins with purebred individuals that have desirable traits, which are then bred with other purebred animals to enhance and preserve superior qualities.
- Methods of artificial selection in animals include inbreeding, linebreeding, and outcrossing.
- Offspring from selective breeding often exhibit hybrid vigor, or increased vigor, though in some cases, the quality may decline.
- A similar process is used in plant breeding, where wild plants are domesticated into uniform and predictable agricultural varieties.
- Plants with beneficial traits like high productivity are selectively bred to maintain and enhance those traits.
- Selective breeding of plants has been practiced for thousands of years for agriculture and is now also used in transgenic plant research involving homozygous genes.
- Although artificial selection is usually intentional, it may occur unintentionally during farming and lead to either desirable or undesirable results.
- Advantages of artificial selection include increased productivity, healthier offspring, and faster and easier analysis of offspring traits.
- Disadvantages include the inability to apply it to an entire population simultaneously and the requirement of controlled environments like laboratories or greenhouses.
- Artificial selection reduces genetic diversity in a population because only the most fit individuals are bred, which increases the proportion of homozygous genotypes.
- Examples of artificial selection include dog breeding to create new breeds and cross-breeding in cash crops such as wheat and rice.
Key Differences (Natural selection vs Artificial selection)
| Basis for Comparison | Natural Selection | Artificial Selection |
|---|---|---|
| Definition | A natural process of adaptation where organisms undergo genetic changes in response to environmental pressures. | A human-controlled process where desirable traits are selected and bred in animals or plants. |
| Process | Natural process | Human-made process |
| Occurs in | Natural populations | Domesticated populations |
| Chances of Survival | Increased for fit organisms | Can be at risk if poorly managed |
| Rate | Slow, over many generations | Fast, effects seen in few generations |
| Controlled by | Nature | Humans |
| Performed on | All living organisms | Selected animals and plants |
| Traits | Adaptive traits | Desirable traits chosen by humans |
| Inheritance | Only beneficial traits passed on | Only selected traits passed on |
| Affects | Entire population | Selected individuals |
| Diversity | Increases genetic diversity | Decreases genetic diversity |
| Evolution | Facilitates evolution and speciation | Does not cause evolution |
| Scale | Wide-scale in nature | Limited to economically important species |
| Hybrid Vigor | May be present | May be reduced |
| Effort | No human effort needed | Requires human effort and cost |
| Genotype | Increases heterozygous genotypes | Increases homozygous genotypes |
| Examples | Long-necked giraffes, bird beak variations | Dog breeding, cross-breeding in wheat and rice |
Examples of natural selection
Selection of long-necked giraffes
- The selection of long-necked giraffes from short-necked giraffes is a well-known example of natural selection.
- Historically, both long-necked and short-necked giraffes coexisted.
- Over time, food sources near the ground became scarce, forcing giraffes to rely on tall trees for leaves.
- Long-necked giraffes could reach the higher leaves easily, while short-necked giraffes could not.
- Due to limited food access, short-necked giraffes began to die out, whereas long-necked giraffes survived and reproduced.
- This scenario illustrates how an environmental change — scarcity of ground-level food — favored the survival of better-adapted individuals.
- As a result, long-necked giraffes became more common in the population through natural selection.
Sexual selection in peacocks
- In peacocks, sexual selection occurs through competition among males to attract female mates.
- Male peacocks develop long, colorful, and eye-catching tails to appeal to female peahens.
- These attractive tails play no direct role in survival, food collection, or reproductive ability.
- However, females prefer males with more dazzling tails, leading to higher mating success for those males.
- As a result, males with more attractive tails are naturally selected over those with shorter or less vibrant tails.
- This type of selection, based on mating preferences rather than survival, is known as sexual selection.
- Similar traits are observed in other birds such as ducks and tropical birds, where males display more decorative features than females.
Examples of artificial selection
Dog breeding
- Dog breeding is a widely practiced form of artificial selection, with evidence suggesting it began around 14,000 years ago.
- In ancient times, dogs were bred primarily to create friendlier, faster, and more useful versions of their wild ancestors.
- These early breeds were selected to improve hunting efficiency and provide better protection for human owners.
- As human needs evolved, the purpose of breeding shifted toward roles like guarding homes and deterring intruders.
- Breeds such as greyhounds were interbred to produce strong, fast, and alert dogs.
- In modern times, the focus of artificial selection has shifted again, with many people keeping dogs as companions.
- As a result, dog breeding today often emphasizes friendly temperaments and appealing appearances, leading to breeds like poodles and bulldogs.
Selection of cash crops
- Artificial selection in crop plants has been practiced for thousands of years to enhance desirable traits.
- The ancestor of modern wheat is believed to be Triticum monococcum or einkorn wheat, first cultivated in Asia around 40,000 years ago.
- Early wheat plants were inbred or crossbred with other species to increase yield, adaptability, and diversity.
- Over time, selective breeding led to the development of various wheat species suited for different uses.
- Today, specific wheat species are grown for distinct purposes — for example, wheat used in beer production differs from that used in pasta and noodles.
- These specialized species were developed by selecting and breeding plants with traits best suited to their intended use.
References and Sources
- Reference.com. (n.d.). Example of artificial selection. Retrieved from https://www.reference.com/science/example-artificial-selection-e3b79282eed27f9f
- HKYER. (n.d.). Lab report – Giraffe natural selection. Retrieved from https://hkyer.weebly.com/lab-report–giraffe.html
- University of California Museum of Paleontology. (n.d.). Understanding evolution: What is natural selection? Retrieved from https://evolution.berkeley.edu/evolibrary/article/evo_25
- Rogers, K. (n.d.). About artificial selection. ThoughtCo. Retrieved from https://www.thoughtco.com/about-artificial-selection-1224495
- Petit, J. (n.d.). Test questions: Artificial selection – Period 4. SlideShare. Retrieved from https://www.slideshare.net/jacquiepetit/test-questions-artificial-selection-period-4
- New Scientist. (n.d.). Natural selection. Retrieved from https://www.newscientist.com/term/natural-selection/
- DifferenceBetween.com. (2019, August 14). Difference between natural selection and artificial selection. Retrieved from https://www.differencebetween.com/difference-between-natural-selection-and-vs-artificial-selection/
- Crystalinks. (n.d.). Plant breeding overview. Retrieved from https://www.crystalinks.com/plantbreeding.html
- Encyclopaedia Britannica. (n.d.). The science of evolution. Retrieved from https://www.britannica.com/science/evolution-scientific-theory/The-science-of-evolution
- BBC Bitesize. (n.d.). Natural selection – Evolution and inheritance. Retrieved from https://www.bbc.co.uk/bitesize/topics/zpffr82/articles/z7hj2nb
- BBC Bitesize. (n.d.). Artificial selection – Selective breeding. Retrieved from https://www.bbc.co.uk/bitesize/guides/zgq96yc/revision/2
- BBC Bitesize. (n.d.). Variation and evolution in organisms. Retrieved from https://www.bbc.co.uk/bitesize/guides/z6trd2p/revision/3
- Viva Differences. (n.d.). Difference between natural and artificial selection. Retrieved from https://vivadifferences.com/difference-between-natural-and-artificial-selection/
- Quizlet. (n.d.). BIO2 Exam 1 Flashcards. Retrieved from https://quizlet.com/74934139/bio2-exam-1-flash-cards/
- YourDictionary. (n.d.). Examples of natural selection. Retrieved from https://examples.yourdictionary.com/examples-of-natural-selection.html
- Coulson, T., et al. (2015). Predicting the evolutionary consequences of trophy hunting on a quantitative trait. Journal of Animal Ecology, 84(2), 356–368. https://doi.org/10.1111/1365-2656.12488
- Wheat Training. (n.d.). Basics of wheat growth and development: Introduction to plant breeding. Retrieved from http://www.wheat-training.com/wp-content/uploads/Wheat_growth/pdfs/Basics-Main-Page-IntroductionPB-website.pdf
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