Evolution

Study the passage below and answer the questions that follow.

Question 1

Choose

Set 2

Set 2

In 1831 Charles Darwin set out on a trip around the world in the HMS Beagle. At the Cape Verde Islands, he saw the fossil remains of sea creatures in the cliffs, many metres above sea level.

The unique forms of life he found on the Galapagos Islands, such as the giant tortoises, convinced him that living organisms had evolved over many millions of years. He noticed that these tortoises were quite different from those found elsewhere in the world. Each island also had a distinct type of tortoise, differing in the shape of the shell and mating behaviour.

Explain how Darwin would have used the example of the tortoises to explain speciation. (4)

Originally there would have been one tortoise population that all looked the same.

There were variations among the tortoises.

When the groups of tortoises became separated they were exposed to different environmental conditions.

Different characteristics were selected for in each group by the environmental conditions to which they were exposed.

Eventually each group became so different from the other that they became totally different species.

How do fossils provide evidence for evolution? (2)

Fossils are the preserved remains of living organisms.

Palaeontologists study the fossils and by comparing and dating them, are able to suggest how organisms may have evolved.

Give ONE reason why there are gaps in the fossil records. (2)

Fossils only form under very specific conditions so most living things leave no trace of their existence.

Darwin noticed different species of tortoises on the Galapagos Islands. Two of these tortoises, which are drawn to scale, are shown below.

Question 2

Tabulate TWO visible differences between the two species of tortoises. (5)

Suggest what tortoise 2 might eat that tortoise 1 will not be able to eat. (1)

Tall plants / shurbs / small trees

The two species of tortoises shown above lived on different islands. Darwin suggested that they might have evolved from a common ancestor. Explain how this could have occurred. (6)

On each island the population of tortoises with variation (long and short) lived under different environmental conditions, different sources of food.

After a period of time each group of tortoises underwent natural selection independently.

On each island only those tortoises with the characteristics (long or short neck) favourable for its own conditions survived.

Continued natural selection results in each island having tortoises that are very different from each other/ they differ genotypically and phenotypically.

Reproductive isolating mechanisms prevent them from interbreeding even if they are allowed to mix i.e. each is a separate sepcies.

The different species of finches (A, B, C and D) below are found on different Galapagos Islands and are thought to have originated from a seed-eating ancestral species from the mainland of South America. They resemble each other with respect to their internal body structure but differ with respect to the shapes and sizes of their beaks and hence their feeding habits.

Question 3

Explain what is meant by geographical isolation of a population. (2)

When a geographical barrier e.g. mountain, river, sea, etc. separates a subpopulation of breeding individuals from the parent population.

Why do you think that different finch species became adapted to eat different food types? (4)

When food shortages developed, only some of the birds were able to find food, since their beaks were slightly different from the rest of the population.

The survivors bred and passed these features onto the next generation, while those poorly adapted died out.

Explain the process by which the different species adapted and evolved to eat different types of food mentioned. (5)

There was a great variety within the species because of genetic variation leading to natural selection.

Many seed eating finches died.

Those finches that were able to eat different foods/non-seed food survived in greater numbers to pass their genes to their offspring.

Species became distinct and adapted to the specific food on that island.

The diagrams below show the heads of four of the many species of finches inhabiting different islands in the Galapagos group, some 1 000km from South America. The number of species of finches on the South American mainland is fewer than that found on the islands.

Question 4

Explain ONE possible reason for the differences in the shape of the beaks. (2)

Adaptation to eat different food / to different environmental conditions / niches (adaptive radiation); OR

Different beaks because of variation in the genotypes: OR

Mutations causes variation in types of beak.

According to Darwin, these finches probably descended from a common ancestral finch species. Give a geological explanation of how this ancestor probably came to be on these islands. (2)

During continental drift/physical separation of the islands from the mainland a part of the original population became isolated on the island; OR

Through strong winds/ocean currents the birds may have been blown/moved from the mainland to the islands.

Explain why there is a lower species diversity of finches on the South American mainland than on the islands. (3)

More food available on mainland. This decreases competition /decreases the effect of natural selection in forming new species; OR

More diverse habitats on islands than on mainland; OR

Less diverse/more stable habitats on mainland than on islands.

Study the different skulls below and then answer the questions that follow.

Question 5

Explain two similarities between the skulls that have evolutionary significance. (2)

Both have a large brain case/cranium.

Both have small canines.

Both have eye sockets at the front of the head.

Tabulate five differences between the two skulls. (6)

H. sapiens are more intelligent than A. afarensis. Give evidence from the skulls of both to support this view. (4)

The cranium of H. sapiens is larger, indicating that they have a larger brain.

The teeth of H. sapiens are fewer and smaller, indicating the ability to use fire to cook food.

Questions source: DBE (Authorisation 11798)

- Greg Gopaul -