30: Evolution II

Question 1

State the two theories of Lamarckism.

Answer 1

1. Environmental changes create needs that cause organisms to modify their structures to meet these needs. Structures which are used repeatedly will become well developed. In contrast, the structures which are not used will degenerate.
2. Acquired characters are passed on to offspring.

Question 2

Describe the evolution of long necks in giraffes according to Lamarckism.

Answer 2

1. Ancestors of giraffes had short necks. During a shortage of grass, giraffes stretched their necks to feed on leaves on trees.
2. Their offspring inherited this character of a long neck. They continued to stretch their necks to feed on leaves on higher branches.
3. Over generations, the accumulated effect of continued neck stretching resulted in long-necked giraffes. Giraffes become more adapted to the environment.

Question 3

Describe an experiment which disproved Lamarckism.

Answer 3

Tails of mice were cut off over many generations. However, mice of each generation were born with complete tails. This showed that acquired characters could not be passed on to offspring.

Question 4

Describe the features of finches on Galapagos Islands in Darwin’s observations.

Answer 4

Their beaks differed in size and shape, and they were adapted to different food sources on individual islands.
Except for beaks, the finches looked similar to one another, ad to species living o the mainland of South America.

Question 5

List 2 observations made by Darwin when studying artificial selection of pigeons.

Answer 5

1. Variations in characteristics existed among pigeons.
2. Some characteristic could be passed on from one generation to subsequent generations.

Question 6

Name the process which occurs in nature to bring about evolution.

Answer 6

Natural selection

Question 7

List 4 key observations in Darwinism.

Answer 7

Observations:
1. Organisms produce more offspring than needed to replace themselves.
2. Populations remain fairly stable in size over time.
3. Variations exist among individuals of the same species.
4. Some variations are inheritable.

Question 8

List 3 deductions based on the observations in Darwinism.

Answer 8

1. Struggle for existence: individuals within a population compete for limited resources (eg. food) for survival.
2. Survival of the fittest: Individuals with favourable characters are better adapted to the environment. They have a higher chance to survive and reproduce.
3. The better adapted individuals pass on their favourable characteristics to their offspring. The proportion of individuals with favourable characters in the population increases in subsequent generations.

Question 9

Describe the relationship between individuals, a population, and natural selection.

Answer 9

Natural selection acts on individuals in a population, so the population changes over generations to become better adapted to the environment.

Question 10

Describe the evolution of long necks in giraffes according to Darwinism.

Answer 10

1. Ancestors of giraffes had variation in neck length. Some had long necks and some had short necks.
2. During a shortage of grass, a long neck is a favourable character. Long-necked giraffes could obtain food and thus has a higher chance to survive and reproduce. Short-necked giraffes died.
3. Long-necked giraffes passed on the character of a long neck to their offspring. The proportion of long-necked giraffes in the population increased in subsequent generations.

Question 11

Explain the meaning of neo-Darwinism.

Answer 11

Neo-Darwinism is the theory of Darwinism while taking modern genetics into account.

Question 12

State the meanings of allele frequency and gene pool.

Answer 12

Allele frequency is the percentage of a particular allele found in a gene pool.
Gene pool is the total of all the alleles of all the genes in a population at a given time.

Question 13

Explain why the number of black peppered moths stayed low before the Industrial Revolution.

Answer 13

In a population of peppered moths, genetic variations in body colour exist among individuals. Before the Industrial Revolution, many trees trunks were covered by lichens, which were light in colour. White peppered moths on these tree trunks were harder for birds to see and eat them. Black peppered moths were not camouflaged and were more lightly to be eaten by birds. Thus, the number of black peppered moths stayed low.

Question 14

Explain why the black peppered moths became the majority during the Industrial Revolution.

Answer 14

During the Industrial Revolution, lichens were killed and tree trunks were darkened by the smoke released from factories. White peppered moths became easier for birds to see and eat. Black peppered moths had a higher chance to survive and reproduce. The black peppered moths produced more offspring and their proportion in the population increased in subsequent generations.

Question 15

Explain why white peppered moths became more common than black peppered moths again in the 1980s.

Answer 15

Air pollution controls have been in effect, and lichens grew on the tree trunks again as air quality improved. Black peppered moths were more easily seen by birds and eaten again. White peppered moths now had a better camouflage and had a higher chance to survive and reproduce. The white peppered moths produced more offspring and their proportion in the population increased in subsequent generations.

Question 16

Name the kinds of resistance which can develop in populations of bacteria and insect pests.

Answer 16

Bacteria: antibiotic resistance
Insect pests: insecticide resistance

Question 17

Explain how many mosquitoes became resistant to insecticide DDT within a few years of widespread usage.

Answer 17

1. In a generation of mosquitoes, genetic variations in resistance to DDT exist among individuals. Most mosquitoes were non-resistant to DDT, while some were DDT-resistant.
2. When DDT was used, the DDT-resistance mosquitoes had a higher chance to survive and reproduce.
3. When DDT was used repeatedly, the proportion of DDT-resistance mosquitoes in the population increased in subsequent generations. As a result, DDT became less effective in killing mosquitoes.

Question 18

Describe the relationship between natural selection and individuals with different phenotypes.

Answer 18

Natural selection eliminates individuals with poorly adapted phenotypes and hence the associated alleles from a population.

Question 19

Explain why sickle-cell anaemia carriers have a selection advantage in areas where Malaria is common.

Answer 19

Sickle-cell anaemia carriers are heterozygotes with both normal and sickle-shapes red blood cells. They do not have the symptoms of sickle-cell anaemia. They are also less likely to have malaria because its pathogen cannot reproduce in sickle-shaped red blood cells. Thus, heterozygotes have a higher change to survive and reproduce, which is a selection advantage.

Question 20

State the meaning of speciation.

Answer 20

Speciation is the development of one or more new species from an existing species.

Question 21

State the definition of species.

Answer 21

A species is a group of organisms which can interbreed and produce fertile offspring.

Question 22

State two steps which can lead to speciation.

Answer 22

1. Isolation of a population into groups.
2. Changes in the population groups’ genetic compositions.

Question 23

List two types of speciation.

Answer 23

1. Allopatric speciation, speciation which requires a geographical barrier.
2. Sympatric speciation, speciation which does not require a geographical barrier.

Question 24

Describe the process of allopatric speciation.

Answer 24

1. A population of species occupied a habitat. The individuals can freely interbreed and produce fertile offspring. They share a common gene pool.
2. The population is separated geographically into groups and the groups become isolated from each other. The isolated groups cannot meet to interbreed and gene flow between them stops.
3. Due to random mutations, genetic variations existing in one isolated group are different from those in another group. If each isolated group faces a different set of environmental conditions, different characters adapted to those particular environmental conditions will be selected by natural selection.
4. Over time, different mutations and different changes in allele frequencies by natural selection accumulate in the isolated groups. Their genetic compositions become so different that the isolated groups can no longer interbreed to produce fertile offspring even if they meet again. They become different species, each with its own gene pool.

Question 25

Describe an example of allopatric speciation.

Answer 25

Camels and llamas: Their ancestral individuals probably migrated from North America to Asia and Africa, and some to South America. The two groups became isolated from each other when continents separated. Different environmental conditions then drop the two groups to evolve differently by natural selection. Over time, their genetic compositions became so different that the two groups were considered as two species.

Question 26

List and explain 4 types of sympatric speciation.

Answer 26

1. Ecological isolation: mutations cause the same species to inhabit similar regions but have different habitat preferences, gradually leading to the formation of new species. 2. Behavioural isolation: mutations cause a change in courtship patterns which attract the opposite sex. 3. Mechanical isolation: mutations in animal genitalia prevent successful copulation; mutations in pollination processes cause the same species of flowers to be pollinated by different animals. 4. Seasonal isolation: mutations cause the same species of plants to pollinate at different seasons.