17.3 Evolution

Fig. 1 below compares the lower jaw of Homo habilis and Homo sapiens according to scale.

Fig. 1

Based on the information above, suggest a reason why wisdom teeth became vestigial structures in Homo sapiens.

Explain why humans still have wisdom teeth, even though it serves no purpose for them.

Wisdom teeth can cause a range of oral health problems in certain people, including gum infections, damage to other teeth and problems with eating due to teeth being pushed out of position by the presence of wisdom teeth. Some scientists believe that this may affect their persistence in future generations.

Predict the possible fate of wisdom teeth in future human populations, based on this information and your knowledge of natural selection.

[1]

Explain your answer at part (i).

[1]

Compare and contrast allopatric and sympatric speciation.

There are 72 known species of the genus Lygodactylus, many of them found on the continent of Africa where they inhabit the same area.

One of these species is the lizard Lygodactylus williamsi which is more commonly known as a dwarf gecko. Scientists were investigating the number of different Lygodactylus species in one part of East Africa.

Describe one way in which scientists could distinguish if the different types of lizards belong to the same species.

The dwarf gecko lives in the leaf crown of screw pine trees, several metres above ground, feeding off insects and drinking water from leaves. These trees are located in forest patches in parts of Africa, especially Tanzania. Demand for timber for firewood and charcoal production in Tanzania is exceptionally high.

Suggest and explain how speciation may occur as a result of deforestation.

Many species of lizards are similar in size and have few differences in their appearance, apart from their colour.

Suggest how the variety of colour patterns displayed by lizards may help to maintain the lizards as separate species.

Rhagoletis pomonella is otherwise known as the apple maggot fly. Initially, these maggots would lay their eggs on hawthorn fruit. In the 19th century a distinct group of maggots emerged that lay their eggs on apples only. Apples and hawthorn fruit are closely related. 

Use this information to suggest how these two species of maggots arose by sympatric speciation.

Renosterveld is a type of vegetation found within South Africa's Cape Floristic Region. Renosterveld is characterised by a variety of species of shrubs and grasses that grow in relatively fertile soil and which make the areas where they grow popular for cultivating crops such as wheat. Renosterveld is home to the endangered geometric tortoise, Psammobates geometricus, which survives in remaining pockets of natural vegetation.

Fig. 1 shows an example of a geometric tortoise.

Image courtesy of the Biodiversity Heritage Library. Licensed under Creative Commons Attribution 2.0 Generic License. Reused and distributed under conditions found at https//creativecommons.org/licenses/by/2.0/deed.en

Fig. 1

Explain how the cultivation of crops could result in speciation within a population of geometric tortoises over time.

Scientists investigated one of these tortoise populations and discovered that most individuals were either very large or very small. Very small individuals were able to hide under shrubs from aerial predators such as peregrine falcons, Falco peregrinus, while large individuals had large shells, making it difficult for aerial predators to get a secure grip on them.

[1]

A large fire swept through the habitat of the tortoise population, destroying all the vegetation. Only fifteen tortoises of the original population survived the fire. They were rescued by volunteers at a reptile sanctuary and released into a small nature reserve where no other geometric tortoises were present. All fifteen tortoises displayed a large phenotype.

Explain the effect that this event would have on the new nature reserve tortoise population.

The allele for large body size (L) is dominant over the allele for small body size (l) in the geometric tortoise.

Explain why there may still be tortoises with small body size appearing in future generations of the nature reserve population that was rescued from the fire.

Mining for gold produces waste material which contains sulfur-bearing minerals. When surface water and shallow groundwater come into contact with these minerals a chemical reaction occurs which produces sulfuric acid. This process is known as acid mine drainage and it can lower the soil pH to a level where very few plants can survive.

Environmentalists studied the area around an abandoned gold mine and discovered a few earleaf acacia, Acacia auriculiformis, individuals surviving in the acidic soil. A. auriculiformis typically occurs in more neutral or alkaline soils.

Explain how natural selection could produce a population of A. auriculiformis that would be tolerant to the acidic soil found around the mine shaft.

A. auriculiformis typically flowers from April to July in its native habitat. Ecologists studied the flowering time of the population of A. auriculiformis that are tolerant to low soil pH and compared it to the flowering time of a population growing in the surrounding habitat which was not tolerant to low soil pH. They measured the density of flowers found on the trees over a period of 180 days from 20 April.

Fig. 1 shows the results of this study.

Fig. 1

Describe the flowering times of normal and acid-tolerant A. auriculiformes.

Describe how the results shown in Fig. 1 could lead to the development of a new species of acacia.

The change in soil pH can lead to the formation of a new species over time.

Define the term 'species'.