Humans and artificial selection

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What is Artificial Selection?

**Artificial selection** (also called **selective breeding**) is the process where humans choose which plants or animals to breed based on desired traits.
Unlike **natural selection**, which is driven by environmental pressures, artificial selection is directed by human goals.
Over many generations, this can produce dramatic changes in a species, such as larger fruits, friendlier pets, or higher milk yields.

Historical Examples

Selective breeding has been practiced since **prehistory**; crops like **wheat, rice, and maize** were domesticated from wild ancestors thousands of years ago.
**Robert Bakewell** (18th century) pioneered scientific selective breeding, creating the **New Leicester sheep** with larger, meatier bodies and finer wool.
Bakewell also bred the **Dishley Longhorn** cattle for beef, doubling the average slaughter weight from 370 lbs (1700) to 840 lbs (1786).
**Charles Darwin** used artificial selection as an analogy for natural selection in×On the Origin of Species×(1859).

Methods of Selective Breeding

Breeders select individuals with **desirable traits** (e.g., size, color, disease resistance) to reproduce, while discouraging breeding of those with undesirable traits.
**Inbreeding** (mating close relatives) can fix desired traits but may increase risk of genetic disorders.
**Crossbreeding** (mating different breeds) can create **hybrids** with combined traits, such as disease resistance and high yield.
Modern techniques include **genetic engineering**, but artificial selection relies on existing genetic variation.

Examples in Plants and Animals

**Dogs**: All dog breeds (e.g., Labrador, Chihuahua) descend from wolves through selective breeding for size, temperament, and abilities.
**Crops**: **Maize (corn)** was bred from the wild grass **teosinte**; modern corn has much larger ears and kernels.
**Livestock**: **Holstein cows** are bred for high milk production; **broiler chickens** grow rapidly for meat.
**Ornamental plants**: Roses, tulips, and orchids have been bred for flower color, shape, and fragrance.

Unintended Consequences

Selective breeding can have **unintended side effects**, such as reduced genetic diversity or health problems (e.g., hip dysplasia in dogs).
Some traits may be linked to others; selecting for one trait can accidentally bring along another (e.g., selecting for larger fruit may reduce flavor).
**Unintentional selection** also occurs: for example, plowing practices may favor larger seeds without conscious choice.

Artificial vs. Natural Selection

**Natural selection** is non‑directed; traits become more common if they improve survival and reproduction in a given environment.
**Artificial selection** is directed by human preferences, often for traits that are not necessarily beneficial in the wild.
Both processes rely on **heritable variation** and **differential reproduction** to change populations over time.

Artificial selection of dogs from wolves has produced many breeds with different traits.

A monohybrid cross showing how dominant and recessive traits are inherited. Breeders can use such crosses to predict offspring traits.

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1.What is the term for the process by which humans choose which plants or animals to breed based on desired traits?
Easy
- AArtificial selection
- BNatural selection
- CEvolution
- DAdaptation
2.Which scientist used artificial selection as an analogy to explain natural selection?
Easy
- ACharles Darwin
- BRobert Bakewell
- CAbu Rayhan Biruni
- DGregor Mendel
3.In selective breeding, what is the term for the offspring of two different purebred animals?
Medium
- ACrossbreed
- BHybrid
- CPurebred
- DVariety
4.Which of the following is an example of unintentional selective breeding?
Medium
- AIncrease in seed size due to ploughing practices
- BBreeding dogs for herding ability
- CSelecting cows that produce more milk
- DGrowing only the largest ears of corn for next year's seed
5.Robert Bakewell's selective breeding of sheep primarily aimed to produce animals with which combination of traits?
Hard
- ALarge, fine-boned, with long lustrous wool
- BSmall, hardy, with short coarse wool
- CFast-growing, with high milk production
- DAggressive, with strong horns
6.What is the name for a domesticated plant that has been developed through selective breeding?
Easy
- ACultivar
- BBreed
- CCrossbreed
- DPurebred
7.Which of the following is NOT a technique used in animal breeding alongside artificial selection?
Medium
- AMutation
- BInbreeding
- CLinebreeding
- DOutcrossing
8.How did the average weight of a bull sold for slaughter change between 1700 and 1786 as a result of selective breeding?
Hard
- AIt more than doubled from 168 kg to 381 kg
- BIt increased slightly from 200 kg to 250 kg
- CIt decreased from 381 kg to 168 kg
- DIt remained the same at about 300 kg

More questions

9.What is the main difference between artificial selection and natural selection?
Easy
- AArtificial selection is directed by humans, while natural selection is non-directed
- BArtificial selection occurs only in plants, while natural selection occurs in animals
- CNatural selection is faster than artificial selection
- DArtificial selection produces no change over time
10.Which ancient civilization is known to have practiced selective breeding, as mentioned in the source?
Medium
- ARomans
- BGreeks
- CEgyptians
- DChinese
11.In the context of selective breeding, what is a 'breed'?
Medium
- AA group of domesticated animals with similar characteristics developed by humans
- BA wild population of animals
- CA type of plant cultivar
- DThe offspring of two different species
12.Which of the following statements about selective breeding is TRUE?
Hard
- ASelective breeding can produce both intended and unintended results
- BSelective breeding always leads to negative outcomes
- CSelective breeding only affects physical traits, not behavior
- DSelective breeding has only been practiced in the last 200 years
13.A farmer selectively breeds cows to produce more milk. Over several generations, the average milk yield increases. Which statement best explains this outcome?
Medium
- AThe farmer's selection caused mutations that increased milk yield.
- BCows that naturally produced more milk were chosen as parents, passing on their genes.
- CAll cows in the herd gradually learned to produce more milk.
- DThe farmer fed the cows a special diet that increased milk production.
14.In 1700, the average weight of a bull sold for slaughter was 370 pounds. By 1786, the average weight had doubled to 840 pounds. What is the approximate percentage increase in average weight over this period?
Hard
- A56%
- B127%
- C227%
- D44%
15.A plant breeder crosses two purebred pea plants: one with tall stems (TT) and one with short stems (tt). Tall is dominant. What will be the phenotype of all offspring in the first generation (F1)?
Medium
- AAll tall
- BAll short
- CHalf tall, half short
- DAll medium height
16.Which of the following best describes a 'crossbreed' in animal breeding?
Medium
- AThe offspring of two purebred animals of different breeds
- BAn animal that has been bred for many generations within the same breed
- CA breed that has been developed by crossing several different species
- DA hybrid plant that results from crossing two different plant varieties
17.A farmer has a flock of sheep with varying wool quality. She selects the five sheep with the finest wool each year to breed. After 10 generations, the average wool quality has improved. Which of the following is most likely true?
Hard
- AThe genetic diversity of the flock has increased.
- BThe frequency of alleles for fine wool has increased in the population.
- CThe sheep have learned to grow finer wool from being handled more.
- DThe environment has become more favorable for wool growth.
18.Charles Darwin used which term to describe the process humans use to select traits in domesticated species?
Easy
- ANatural selection
- BArtificial selection
- CEvolutionary selection
- DDomestication selection
19.A graph shows the average weight of bulls sold for slaughter in England from 1700 to 1786. The line rises steadily from 370 pounds to 840 pounds. What does this trend most likely indicate?
Medium
- ABulls were eating more nutritious food over time.
- BSelective breeding by farmers like Robert Bakewell increased the size of cattle.
- CThe climate became warmer, causing cattle to grow larger.
- DThe method of weighing bulls became more accurate.
20.A farmer wants to develop a strain of wheat that is resistant to a fungal disease. Which of the following strategies would be most effective?
Hard
- ASpray the entire field with fungicide every year.
- BPlant the wheat in soil that contains the fungus to encourage resistance.
- CSelect and breed only those wheat plants that survive exposure to the fungus.
- DCross wheat with a completely different species of grass.
21.What is the name given to a domesticated plant that has been developed through selective breeding?
Easy
- ABreed
- BCultivar
- CSpecies
- DHybrid
22.Which of the following is a potential disadvantage of selective breeding?
Medium
- AIt can lead to a loss of genetic diversity.
- BIt always produces offspring that are less healthy.
- CIt takes too long to see any results.
- DIt is only possible with plants, not animals.
23.A study compares two populations of chickens: one from a commercial farm that has been selectively bred for egg production for 50 years, and one from a wild jungle fowl population. Which difference would you most likely observe?
Hard
- AThe commercial chickens lay more eggs per year.
- BThe commercial chickens have greater genetic diversity.
- CThe wild chickens lay larger eggs.
- DThe wild chickens are more resistant to all diseases.
24.A farmer wants to develop a strain of wheat that is resistant to a fungal disease. She plants seeds from 100 wheat plants, then after harvest she collects seeds only from the plants that showed the least disease. She repeats this process for several generations. This is an example of which process?
Medium
- ANatural selection
- BArtificial selection
- CGenetic engineering
- DMutation breeding
25.In a selective breeding experiment, a scientist starts with a population of plants that have an average height of 20 cm. She selects the tallest 10% of plants each generation and breeds them together. After 10 generations, the average height is 45 cm. Which of the following best explains why the height stopped increasing after generation 10?
Hard
- AThe plants reached the maximum height possible for that species.
- BThe selection pressure was too weak to cause further change.
- CThe genetic variation for height was exhausted in the population.
- DThe environment changed, preventing further growth.
26.A dog breeder wants to produce puppies with a specific coat color. She mates a male dog with a black coat to a female dog with a brown coat. All the puppies have black coats. She then mates those black-coated puppies with each other. In the next generation, some puppies have brown coats. What does this outcome indicate about the black coat allele?
Medium
- AIt is recessive to the brown allele.
- BIt is dominant over the brown allele.
- CIt is codominant with the brown allele.
- DIt is not inherited in a predictable pattern.
27.A farmer has a flock of sheep with varying wool quality. She selects the five sheep with the finest wool each year to breed. After 10 generations, the average wool quality has improved significantly. However, the sheep also become more susceptible to a skin disease. Which of the following best explains this?
Medium
- AThe skin disease is caused by the fine wool trait directly.
- BSelective breeding for one trait can unintentionally affect other traits.
- CThe farmer accidentally selected sheep that were immune to the disease.
- DThe sheep developed the disease because they were inbred.
28.In the 18th century, Robert Bakewell selectively bred cattle. Before his methods, the average weight of a bull sold for slaughter was 370 pounds. By 1786, the average weight was 840 pounds. What is the approximate percentage increase in average weight?
Hard
- A44%
- B127%
- C227%
- D470%
29.A plant breeder crosses a purebred tall pea plant (TT) with a purebred short pea plant (tt). Tall is dominant. The resulting offspring are all tall. He then crosses two of these tall offspring. What is the expected ratio of tall to short plants in the next generation?
Medium
- A1 tall : 1 short
- B3 tall : 1 short
- CAll tall
- D1 tall : 3 short
30.Charles Darwin used the term 'artificial selection' to describe which process?
Easy
- AThe natural process by which organisms adapt to their environment.
- BThe process by which humans breed plants and animals for desired traits.
- CThe process by which species become extinct due to human activity.
- DThe process by which new species arise without human intervention.
31.A scientist is studying a population of wildflowers. She notices that over several years, the average flower color becomes darker. She suspects this is due to natural selection. To test whether artificial selection could produce a similar result, she should:
Medium
- AObserve the flowers without any intervention.
- BCollect seeds from the darkest flowers and plant them in a separate field.
- CIntroduce a predator that eats light-colored flowers.
- DMeasure the soil pH and nutrient levels.
32.A farmer uses artificial selection to increase milk production in his cows. After many generations, the average milk yield per cow has increased by 50%. However, the cows now have a higher incidence of udder infections. Which of the following is the most likely explanation?
Hard
- AThe udder infections are caused by the increased milk yield.
- BThe genes for high milk yield are linked to genes that reduce immune function.
- CThe farmer did not provide enough antibiotics to the cows.
- DThe cows are producing more milk because they are eating more.
33.A student wants to investigate whether artificial selection can change the size of bean seeds. She plants 100 bean seeds, measures the diameter of each mature bean, and selects the 10 largest beans to plant for the next generation. She repeats this for three generations. Which of the following should she do to ensure her results are due to selection and not environmental factors?
Medium
- AUse different soil for each generation.
- BWater the plants with different amounts of water each generation.
- CGrow a control group of beans from unselected seeds under the same conditions.
- DMeasure the beans only at the end of the experiment.
34.A farmer selectively breeds maize plants for larger kernels. After several generations, the average kernel size increases. However, the farmer notices that the plants become more susceptible to a fungal disease. Which of the following best explains this?
Medium
- ASelective breeding for one trait can reduce genetic diversity, making the population more vulnerable to diseases.
- BThe fungal disease mutated to attack larger kernels.
- CLarger kernels require more nutrients, weakening the plant's immune system.
- DThe farmer accidentally selected plants with lower disease resistance.
35.In a selective breeding experiment, a scientist starts with a population of plants that have an average height of 20 cm. She selects the tallest 10% of plants each generation to breed. After 5 generations, the average height is 35 cm. If the heritability of height is 0.5, what is the approximate selection differential per generation?
Hard
- A15 cm
- B7.5 cm
- C30 cm
- D3 cm
36.A graph shows the average weight of bulls sold for slaughter in England from 1700 to 1786. The line rises steadily from 370 pounds to 840 pounds. What does this graph most directly demonstrate?
Medium
- AThe effect of natural selection on bull weight
- BThe impact of selective breeding on bull weight
- CThe increase in food availability for bulls
- DThe evolution of bulls in the wild
37.A plant breeder crosses a purebred tall pea plant (TT) with a purebred short pea plant (tt). Tall is dominant. The resulting offspring are all tall. He then crosses two of these offspring. What proportion of the second generation will be short?
Medium
- A0%
- B25%
- C50%
- D100%
38.A study compares two populations of chickens: one from a commercial farm that has been selectively bred for egg production for 50 years, and one from a wild jungle fowl population. Which of the following differences is most likely to be observed?
Hard
- AThe commercial chickens have greater genetic diversity.
- BThe jungle fowl lay more eggs per year.
- CThe commercial chickens have a narrower range of egg production rates.
- DThe jungle fowl are heavier on average.
39.In the 18th century, Robert Bakewell selectively bred cattle. Before his methods, the average weight of a bull sold for slaughter was 370 pounds. By 1786, the average weight was 840 pounds. What is the percentage increase in average weight?
Medium
- A127%
- B56%
- C227%
- D44%
40.A farmer wants to develop a strain of wheat that is resistant to a fungal disease. She plants seeds from 100 wheat plants, then after harvest she collects seeds from the 10 plants that show the least disease damage. She repeats this for 10 generations. This process is an example of:
Hard
- ANatural selection
- BArtificial selection
- CGenetic engineering
- DMutation breeding

Revision notes

## Humans and Artificial Selection Artificial selection (selective breeding) is when humans choose which plants or animals to breed together to get desired traits. This changes the traits of a population over time. - **Process**: Humans select individuals with desirable characteristics (e.g., larger seeds, better wool) and breed them. Offspring inherit those traits. Over generations, the population changes. - **Examples**: Dogs, cats, cattle, wheat, rice, maize. Maize was bred from teosinte. Robert Bakewell improved sheep (New Leicester) and cattle (Dishley Longhorn) in the 1700s, doubling bull weight from 370 to 840 pounds. - **Unintentional selection**: Sometimes traits change due to human practices (e.g., ploughing) without deliberate breeding. - **Key terms**: Breeds (animals), varieties/cultivars (plants), crossbreed/hybrid (offspring of different breeds). - **Darwin**: Used artificial selection as an analogy for natural selection. He wrote: "if feeble man can do much by his powers of artificial selection, I can see no limit to the amount of change... which may be effected... by nature's power of selection." - **Technologies**: Inbreeding, linebreeding, outcrossing are methods used in animal breeding. **Important**: Artificial selection is directed by humans; natural selection is non‑directed.

Artificial selection: The process by which humans breed plants or animals for specific phenotypic traits by choosing which individuals reproduce.
Selective breeding: Another name for artificial selection; humans select which individuals to breed to produce desired traits.
Breed: A group of domesticated animals with similar characteristics, produced by selective breeding.
Variety / Cultivar: A type of domesticated plant developed by selective breeding.
Crossbreed / Hybrid: Offspring from two different breeds (animals) or varieties (plants).
Inbreeding: Breeding between closely related individuals to maintain desired traits.
Linebreeding: A form of inbreeding that keeps offspring related to a particular ancestor.
Outcrossing: Breeding between unrelated individuals to introduce new traits.

Flashcards

What is selective breeding?

Selective breeding (artificial selection) is the process by which humans choose which animals or plants to reproduce to develop specific traits.

What is another name for selective breeding?

Artificial selection.

What are domesticated animals called in selective breeding?

Breeds.

What are domesticated plants called in selective breeding?

Varieties, cultigens, cultivars, or breeds.

What is a crossbreed?

A crossbreed is the offspring of two purebred animals of different breeds. In plants, crossbred plants are called hybrids.

Who discussed selective breeding in On the Origin of Species?

Charles Darwin.

How did Darwin use artificial selection in his theory?

Darwin used artificial selection as an analogy to explain natural selection, but noted that natural selection is non-directed.

Can selective breeding be unintentional?

Yes, selective breeding can be unintentional, for example, when farming practices inadvertently favor certain traits.

Give an example of unintentional selective breeding.

In some grains, an increase in seed size may have resulted from certain ploughing practices rather than intentional selection.

Since when has selective breeding been practiced?

Since prehistory.

Name a crop that required large changes from its wild form through selective breeding.

Maize (corn), which was selectively bred from teosinte in Mesoamerica.

Who established selective breeding as a scientific practice in the 18th century?

Robert Bakewell during the British Agricultural Revolution.

What sheep breed did Robert Bakewell improve?

The Lincoln Longwool, which he used to develop the New Leicester (Dishley Leicester) sheep.

What characteristics did Bakewell select for in sheep?

Large, fine-boned sheep with long, lustrous wool.

How did Bakewell change cattle breeding?

He was the first to breed cattle primarily for beef, creating the Dishley Longhorn.

How did the average weight of bulls change from 1700 to 1786 due to selective breeding?

It increased from 370 pounds (168 kg) to 840 pounds (381 kg).

What horse breed did Bakewell develop?

The Improved Black Cart horse, later known as the Shire horse.

What term did Charles Darwin coin for selective breeding?

Selective breeding (he used 'artificial selection' in his book).

What is the difference between artificial selection and natural selection?

Artificial selection is directed by humans to produce desired traits, while natural selection is non-directed and driven by environmental pressures.

Name two techniques used in animal breeding alongside artificial selection.

Inbreeding, linebreeding, and outcrossing (any two).

What is the purpose of selective breeding in agriculture?

To develop plants and animals with desirable traits such as higher yield, disease resistance, or specific physical characteristics.

How did ancient Romans contribute to selective breeding?

They practiced selective breeding and wrote treatises advising on selecting animals for different purposes.

What did the 11th-century scholar Abu Rayhan Biruni write about selective breeding?

He noted the idea in his book India, giving examples like farmers selecting corn and beekeepers culling unproductive bees.

What is the modern breed that descended from Bakewell's New Leicester sheep?

The English Leicester (or Leicester Longwool), primarily kept for wool production.

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