Evolution & Speciation

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Evolution

Evolution is defined as changes in the heritable characteristics of organisms over generations.
Heritable characteristics are determined by alleles of genes and can be passed to offspring; non-inherited changes (e.g. leaves eaten) do not cause evolution.
Random mutation can create new alleles that are more or less advantageous.
Advantageous heritable characteristics are more likely to be passed on, leading to gradual change in a species over time — this is natural selection.
Evolution can lead to the development of completely new species, increasing diversity; theoretically all life originated from a single species.

Evolution of the horse

Theories of Evolution: Darwin and Lamarck

Darwin's theory of evolution by natural selection states: individuals show variation due to random mutations; they compete for survival due to selection pressures; those with advantageous characteristics survive and reproduce more; advantageous alleles become more frequent over generations.
Darwinian evolution requires that characteristics are heritable.
Lamarck's theory proposed that changes acquired during an organism's lifetime (acquired characteristics) can be inherited, e.g. giraffes stretching their necks.
Lamarck's ideas were incorrect because acquired characteristics are not passed on to offspring; the new science of epigenetics may provide a minor exception.
Darwin's theory has been updated: evolution is not always slow (e.g. antibiotic resistance in bacteria) and the fossil record does provide evidence (e.g. intermediate species).

Evidence of Evolution: Sequence Data

Sequence data can be obtained from DNA (nuclear, mitochondrial, chloroplast), RNA, and proteins.
Similarities in sequence data between species suggest they share a common ancestor.
Comparisons must use the same part of the DNA, often from highly conserved regions that change very little over time (e.g. genes for haemoglobin or respiratory enzymes).
DNA is extracted from blood, skin, or fossilised remains, then sequenced and compared; more similarities mean closer evolutionary relationship.
Example: humans and chimpanzees share almost 99% of their DNA sequences, making them our closest living relatives.
Data from multiple sources (e.g. several genes) increases certainty and can be used to build an evolutionary tree.

Evidence of Evolution: Selective Breeding

Selective breeding (artificial selection) is when humans choose organisms with desirable characteristics and breed them together repeatedly over many generations.
It takes advantage of naturally occurring variation, e.g. higher food yield or disease resistance in plants, or heavy wool or high milk production in animals.
In artificial selection, desirable alleles are passed on because humans decide which individuals breed; in natural selection, advantageous alleles increase survival.
Selective breeding leads to faster change than natural selection because only selected individuals breed together.
It provides evidence that evolution occurs due to accumulation of small changes to DNA over time.
Process: (1) population shows variation; (2) breeders select desired individuals; (3) breed them together; (4) test offspring and select best; (5) repeat over many generations until all offspring show desired characteristics.

Selective breeding in dogs

Evidence of Evolution: Homologous Structures

Homologous structures are body parts that may look and function differently but share structural similarities, e.g. limbs of birds, bats, crocodiles, whales, horses, and monkeys.
One explanation is adaptive radiation: organisms with homologous structures evolved from a shared common ancestor and adapted to different environments.
A pentadactyl limb has five digits (fingers or toes) and is found in many mammals, birds, amphibians, and reptiles.
In different species, the pentadactyl limb has a similar bone layout but enables different modes of movement, e.g. human foot for upright walking, whale flipper for swimming, bird wing for flight.
The individual bones may differ in shape and size, but their layout is almost exactly the same.

Homologous limb structures

Convergent Evolution

Analogous structures have similar form and function but different evolutionary origins.
They arise from convergent evolution, which occurs when distantly related species live in habitats with similar selection pressures.
Analogous structures provide evidence for the passing on of advantageous characteristics during natural selection.
Example: dolphins (mammals) and sharks (fish) share a streamlined body shape, but evolved separately.
Example: cacti (Americas) and euphorbias (Africa) are desert plants with spiny leaves and succulent stems, but belong to different orders and evolved separately.

Speciation

Speciation is the development of new species from pre-existing species over time.
Speciation increases diversity; extinction reduces it (e.g. passenger pigeon, woolly mammoth).
Speciation occurs when gene flow between populations is prevented, e.g. by separation on different islands.
When gene flow stops, genetic differences accumulate, especially if different selection pressures act on the populations.
Speciation has occurred when the two populations can no longer interbreed to produce fertile offspring; they are reproductively isolated.
Reproductive isolation alone is not enough for speciation; gradual evolutionary change must also occur.

Reproductive Isolation and Differential Selection

Reproductive isolation occurs when changes in alleles and phenotypes prevent individuals from successfully breeding with others.
Examples of changes leading to reproductive isolation: seasonal changes (different mating or flowering seasons) and behavioural changes (altered courtship behaviours).
Geographical isolation occurs when populations are separated by barriers such as bodies of water, mountain ranges, or man-made barriers like motorways.
Geographical isolation prevents gene exchange; the two populations may experience different selection pressures — this is differential selection.
Over time, the populations may become so different that they are reproductively isolated, and speciation has occurred.
Example: bonobos (south of Congo river) and chimpanzees (north) became geographically isolated, experienced differential selection, and eventually became separate species.

Types of Speciation

Allopatric speciation occurs as a result of geographical isolation and is the most common type.
In allopatric speciation, barriers (natural or man-made) prevent gene flow; allele frequencies change due to different selection pressures and genetic drift.
If enough allele frequency differences arise, the populations become reproductively isolated and are separate species.
Sympatric speciation takes place with no geographical barrier; isolation occurs when random changes in alleles/phenotypes prevent breeding within the same area.
Examples of sympatric isolation: temporal isolation (different mating/flowering seasons) and behavioural isolation (changed courtship behaviours).
Example: sympatric speciation in fruit flies — a random mutation changes food preference, preventing interbreeding and leading to separate species.

Preventing Hybridisation

A species is a group of organisms with similar characteristics that can interbreed to produce fertile offspring.
A hybrid is the offspring of individuals of two different species; hybrids are rare and usually infertile.
Incompatible chromosome numbers can prevent hybridisation: gametes with different chromosome numbers fuse, producing zygotes with uneven chromosomes that cannot pair during meiosis, causing infertility.
Example: mating a horse and donkey produces a mule, which has an odd number of chromosomes and cannot carry out meiosis, so is sterile.
Incompatible courtship behaviours prevent mating and thus hybridisation, e.g. intricate courtship rituals in birds of paradise.

Adaptive Radiation

Adaptive radiation is the rapid evolution of multiple species from a common ancestor due to natural selection.
New species may have similar features due to shared ancestry but differ in ways that allow them to fill different ecological niches.
An organism's ecological niche is its role in the ecosystem, e.g. food eaten, environmental conditions required, predators it feeds.
Examples: Darwin's finches in the Galapagos islands and Hawaiian honeycreepers (more than 50 species).
Some Hawaiian honeycreepers can co-exist on the same island because they fill different niches.

Speciation in Plants

In most cases speciation is slow, but in some plants it can happen within a single generation — abrupt (instant) speciation.
This is possible because plant cells can remain viable when polyploid (more than two sets of chromosomes), e.g. 3n triploid, 4n tetraploid.
Autopolyploidy arises within a single species when chromosomes fail to separate during meiosis (nondisjunction), producing diploid gametes that can fuse to form 3n or 4n zygotes.
Allopolyploidy arises when diploid gametes from two different species fuse, producing a polyploid hybrid.
Polyploidy can be advantageous: it may allow otherwise infertile hybrids to carry out meiosis, polyploid plants are often larger and more vigorous, and extra gene copies mask harmful mutations.
A 4n individual produces 2n gametes and cannot breed with 2n individuals to produce fertile offspring (a 2n gamete + n gamete = infertile 3n zygote), so it is a new species.
Examples: Persicaria species include diploid, tetraploid, and hexaploid types; Fallopia includes octoploid (Japanese knotweed), tetraploid (giant knotweed), and hexaploid (Bohemian knotweed, a hybrid).

Teosinte and modern corn

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1.Which of the following best defines evolution?
Easy
- AChanges in the heritable characteristics of organisms over generations
- BChanges in the non-heritable characteristics of organisms during their lifetime
- CThe development of new species from pre-existing species over time
- DThe process by which organisms become better adapted to their environment during their lifetime
2.Which of the following is the mechanism that drives evolution?
Easy
- ANatural selection
- BMutation
- CGenetic drift
- DSelective breeding
3.Which of the following are sources of evidence for evolution? (select all that apply)
Medium
- ASelective breeding
- BSequence data
- CHomologous structures
- DAcquired characteristics
- EAnalogous structures
4.Evolution can be defined as changes in the heritable characteristics of organisms over generations.
Easy
True or false?
5.Lamarck's theory of evolution by acquired characteristics is supported by modern evidence.
Easy
True or false?
6.Which of the following is an example of a homologous structure?
Medium
- AThe pentadactyl limb of a human and the flipper of a whale
- BThe wing of a butterfly and the wing of a bat
- CThe streamlined body shape of a dolphin and a shark
- DThe spines of a cactus and the spines of a euphorbia
7.Which of the following is an example of an analogous structure?
Medium
- AThe wing of a butterfly and the wing of a bat
- BThe pentadactyl limb of a human and the flipper of a whale
- CThe bone structure of a bird wing and a crocodile limb
- DThe leaves of a cactus and the leaves of a euphorbia
8.Which of the following best defines speciation?
Medium
- AThe development of new species from pre-existing species over time
- BThe formation of hybrids between two different species
- CThe gradual change in allele frequencies within a population
- DThe extinction of a species due to environmental changes

Plus de questions

9.Which of the following is an example of allopatric speciation?
Medium
- ATwo populations of trees separated by a mountain range become different species
- BTwo populations of fruit flies in the same laboratory develop different food preferences and become different species
- CTwo populations of plants in the same area develop different flowering seasons and become different species
- DTwo populations of birds in the same forest develop different courtship behaviours and become different species
10.Which of the following is an example of sympatric speciation?
Medium
- ATwo populations of fruit flies in the same laboratory develop different food preferences and become different species
- BTwo populations of trees separated by a mountain range become different species
- CTwo populations of fish separated by a waterfall become different species
- DTwo populations of mammals separated by a river become different species
11.Which of the following are barriers to hybridisation? (select all that apply)
Medium
- AIncompatible chromosome numbers
- BIncompatible courtship behaviours
- CGeographical isolation
- DTemporal isolation
- EBehavioural isolation
12.Polyploidy can lead to the formation of new plant species within a single generation.
Easy
True or false?
13.Match each term with its correct definition.
Medium
- Evolution
- Speciation
- Selective breeding
- Adaptive radiation
- Changes in the heritable characteristics of organisms over generations
- The development of new species from pre-existing species over time
- Humans choose organisms with desirable characteristics and breed them together
- Rapid evolution of multiple species from a common ancestor
14.Place the following steps of selective breeding in the correct order.
Medium
- The population shows variation; there are individuals with different characteristics.
- Breeders select individuals with the desired characteristics.
- Two selected individuals are bred together.
- The offspring produced reach maturity and are then tested for the desirable characteristics; those that display the desired characteristics to the greatest extent are selected for further breeding.
- The process is repeated over many generations; the best individuals from the offspring are continually chosen for breeding until all offspring display the desirable characteristics.
15.Which of the following are types of evidence that support the theory of evolution? (select all that apply)
Medium
- ASequence data from DNA, RNA and proteins
- BSelective breeding of domesticated plants and animals
- CHomologous structures such as the pentadactyl limb
- DAnalogous structures such as the streamlined body shape of sharks and dolphins
- EAcquired characteristics developed during an organism's lifetime
16.Which of the following best describes the difference between homologous and analogous structures?
Medium
- AHomologous structures share a common ancestry but may have different functions; analogous structures have similar functions but different evolutionary origins.
- BHomologous structures have similar functions but different evolutionary origins; analogous structures share a common ancestry but may have different functions.
- CHomologous structures are always found in the same species; analogous structures are found in different species.
- DHomologous structures are the result of convergent evolution; analogous structures are the result of adaptive radiation.
17.Analogous structures provide evidence for shared ancestry.
Easy
True or false?
18.A population of trees is divided by a new mountain range. Over thousands of years, the two populations become reproductively isolated. Which type of speciation is this?
Medium
- AAllopatric speciation
- BSympatric speciation
- CAdaptive radiation
- DConvergent evolution
19.Place the following events of allopatric speciation in the correct order.
Medium
- A geographical barrier forms, separating a population into two.
- Gene flow between the two populations stops.
- Different selection pressures act on the two populations.
- Allele frequencies change in each population.
- Reproductive isolation occurs and new species form.
20.A population of beetles lives in a forest. Over many generations, the average body size of the beetles increases. Which statement best explains why this change is an example of evolution?
Medium
- ABody size is a heritable characteristic that has changed over generations.
- BThe beetles grew larger during their lifetime because of the food they ate.
- CThe beetles chose to become larger to survive better.
- DBody size is not inherited, so this is not evolution.
21.A scientist compares the amino acid sequence of a protein found in three species. Species X and Y differ by 2 amino acids; species X and Z differ by 15 amino acids. What is the most valid conclusion?
Medium
- ASpecies X and Y are more closely related than species X and Z.
- BSpecies X and Z are more closely related because they have more differences.
- CSpecies Y and Z are the same species.
- DThe protein sequences cannot be used to infer evolutionary relationships.
22.Two plant species that live in the same desert both have thick, succulent stems and spines instead of leaves. They belong to different orders of plants. Which statement best explains this observation?
Medium
- AThe structures are analogous and arose by convergent evolution.
- BThe structures are homologous and show shared ancestry.
- CThe structures are analogous and show shared ancestry.
- DThe structures are homologous and arose by convergent evolution.
23.A horse has 64 chromosomes and a donkey has 62 chromosomes. A mule is produced when they mate. Why is a mule usually infertile?
Medium
- AMules have an odd number of chromosomes that cannot pair up during meiosis.
- BMules have too many chromosomes to carry out mitosis.
- CMules cannot produce gametes because they are diploid.
- DMules have incompatible courtship behaviours.
24.In a population of fruit flies in a laboratory, a random mutation causes some individuals to prefer a different food source. These individuals no longer mate with the rest of the population. Over time, the two groups become separate species. Which type of speciation is this?
Medium
- ASympatric speciation
- BAllopatric speciation
- CGeographical speciation
- DAdaptive radiation
25.Which of the following are examples of evidence that support the theory of evolution? (select all that apply)
Medium
- ADNA base sequence similarities between species
- BThe fossil record showing intermediate species
- CSelective breeding producing new varieties
- DA plant losing its leaves after being eaten by herbivores
- ESimilar amino acid sequences in a conserved protein
26.A population of trees is divided by a new mountain range. Which of the following could contribute to the two populations becoming separate species? (select all that apply)
Hard
- ADifferent selection pressures acting on the two populations
- BGenetic drift causing random changes in allele frequencies
- CGene flow continuing between the two populations
- DThe accumulation of different alleles in each population
- EThe two populations interbreeding freely
27.Two populations that are geographically isolated are always reproductively isolated.
Easy
True or false?
28.A polyploid plant can produce fertile offspring when it breeds with a diploid plant from the parent population.
Medium
True or false?
29.Match each term with its correct description.
Medium
- Homologous structures
- Analogous structures
- Convergent evolution
- Adaptive radiation
- Structures with similar form and function but different evolutionary origin
- Rapid evolution of multiple species from a common ancestor
- Structures that share structural similarities but may look and function differently
- Evolution of similar characteristics in distantly related species living in similar habitats
30.Place the following steps of natural selection in the correct order.
Medium
- Individuals with advantageous characteristics are more likely to survive and reproduce.
- There is variation within a population due to random mutations.
- Advantageous alleles become more frequent in the population over many generations.
- Advantageous alleles are passed on to offspring.
31.Which conclusion is best supported by the data?
Medium
- ACave fish have smaller eyes and smaller bodies than open-air fish, which is consistent with reduced energy expenditure.
- BCave fish have larger eyes and smaller bodies than open-air fish.
- CThere is no difference in eye diameter between the two groups.
- DOpen-air fish have smaller eyes and smaller bodies than cave fish.
32.A scientist wants to compare DNA base sequences from two species to determine how closely related they are. Which of the following is the most important reason for choosing a highly conserved region of DNA for this comparison?
Hard
- AConserved regions are more likely to exist in a wide range of species and have few differences, making similarities and differences easy to identify.
- BConserved regions evolve very quickly, so they show recent evolutionary changes.
- CConserved regions are found only in mitochondrial DNA, which is easier to extract.
- DConserved regions code for proteins that are not essential, so they can vary freely between species.
33.A student is planning an investigation to compare the genetic diversity of two fish populations living in different parts of a cave system. Which of the following would be appropriate steps to increase the reliability of the conclusions? (select all that apply)
Hard
- ACompare the base sequences of several different genes from each population.
- BUse a large sample size from each population.
- CCompare only one gene from one individual in each population.
- DEnsure that the same region of DNA is compared between the two populations.
- EAssume that any differences in allele frequencies are due to environmental factors.
34.Geographical isolation always leads to reproductive isolation and speciation.
Medium
True or false?
35.Match each term with its correct example.
Medium
- Homologous structures
- Analogous structures
- Convergent evolution
- Adaptive radiation
- Pentadactyl limbs of humans, whales and birds
- Streamlined body shape of dolphins and sharks
- Similar body shape evolving separately in dolphins and sharks
- Darwin's finches evolving from a common ancestor to fill different niches
36.Place the following steps of allopatric speciation in the correct order.
Medium
- A geographical barrier separates a population into two.
- Gene flow between the two populations stops.
- Different selection pressures act on each population.
- Allele frequencies change independently in each population.
- Reproductive isolation occurs and two species have formed.
37.A researcher studying cave fish finds that the cave population has a much higher percentage of allele C (100%) compared to the open-air population (0%). Which of the following is the most likely explanation for this difference?
Hard
- AThe cave environment exerts different selection pressures, so allele C may be advantageous in the cave.
- BAllele C is a mutation that occurred only in the cave fish and is always harmful.
- CThe open-air fish have a larger population, so they cannot have allele C.
- DAllele C causes the fish to be infertile in the open air.
38.Which of the following statements about selective breeding are correct? (select all that apply)
Hard
- ASelective breeding is also known as artificial selection.
- BSelective breeding leads to faster change than natural selection.
- CSelective breeding relies on naturally occurring variation.
- DSelective breeding creates new alleles that were not present before.
- ESelective breeding is an example of evolution in action.
39.Which scientist proposed the theory of evolution by natural selection?
Easy
- ACharles Darwin
- BJean-Baptiste Lamarck
- CGregor Mendel
- DAlfred Russel Wallace
40.What is the name of the process by which humans choose organisms with desirable characteristics and breed them together repeatedly?
Easy
- ANatural selection
- BSelective breeding
- CGenetic drift
- DMutation
41.What is the term for a group of organisms with similar characteristics that can interbreed to produce fertile offspring?
Easy
42.What is the term for a limb that has five digits, i.e. five fingers or toes?
Medium
43.What is the term for the process by which humans choose organisms with desirable characteristics and breed them together repeatedly?
Medium
44.Calculate the percentage decrease in the population of apple maggot flies from 1995 to 2015. The population in 1995 was 45,000 and in 2015 was 7,000. Give your answer to the nearest whole number.
Medium
45.Complete the following sentences about types of speciation.
Medium
Speciation that occurs as a result of geographical isolation is known as ____ speciation. Speciation that occurs without a geographical barrier is known as ____ speciation.
46.Complete the sentence about evidence for evolution.
Medium
Similarities in DNA base sequences between species suggest that they share a common ____.
47.Complete the sentence about barriers to hybridisation.
Medium
A mule is an example of a hybrid that is infertile because it has an ____ number of chromosomes, which cannot pair up during ____.
48.A population of apple maggot flies decreased from 45,000 in 1995 to 7,000 in 2015. Calculate the percentage decrease. Give your answer to the nearest whole number.
Medium
49.In a study of fish, the mean eye diameter of fish in the open air was 0.23 mm and in the cave was 0.10 mm. Calculate the percentage decrease in mean eye diameter for cave fish compared with open-air fish. Give your answer to the nearest whole number.
Medium
50.What is the term for a cell that has more than two sets of chromosomes?
Medium
51.Calculate the percentage decrease in mean body length of cave fish compared with open-air fish. Give your answer to the nearest whole number.
Medium
52.State the term for the mechanism by which humans choose organisms with desirable characteristics and breed them together repeatedly.
Easy
53.Explain how isolation can result in the development of a new species.
Hard
54.Explain how polyploidy can lead to the formation of new plant species.
Hard
55.Outline the process of selective breeding.
Medium
56.Scientists studying plant species in Svalbard found that polyploidy was more common in species adapted to extreme cold environments. Suggest why inbreeding is common in these plant groups and explain how polyploidy could buffer its effects.
Challenge
57.Calculate the percentage decrease in the population of apple maggot flies from 1995 to 2015. The population in 1995 was 45,000 and in 2015 was 7,000. Give your answer to the nearest whole number.
Medium
- A92 %
- B100 %
- C76 %
- D84 %
58.A population of apple maggot flies decreased from 45,000 in 1995 to 7,000 in 2015. Calculate the percentage decrease. Give your answer to the nearest whole number.
Medium
- A92 %
- B100 %
- C76 %
- D84 %
59.In a study of fish, the mean eye diameter of fish in the open air was 0.23 mm and in the cave was 0.10 mm. Calculate the percentage decrease in mean eye diameter for cave fish compared with open-air fish. Give your answer to the nearest whole number.
Medium
- A57 %
- B63 %
- C51 %
- D69 %
60.Calculate the percentage decrease in mean body length of cave fish compared with open-air fish. Give your answer to the nearest whole number.
Medium
- A37 %
- B31 %
- C28 %
- D34 %

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