Evolution and Its Mechanisms

Who was the Scientist most famous for his study of natural selection and evolution?

• Theodor Schwann

• Robert Hooke

• Charles Darwin

• Rudolf Virchow

Answer explanation

Charles Darwin is renowned for his theory of natural selection, which explains how species evolve over time. His work laid the foundation for modern evolutionary biology, distinguishing him from other scientists listed.

Lake Victoria in East Africa is home to many species of fish called cichlids. In 1954 the predatory Nile perch was introduced to Lake Victoria. The Nile perch became the dominant fish species in the lake by the mid-1980s. The number of cichlid species in the lake decreased as the Nile perch population increased. The perch preyed heavily on cichlid species that fed on algae and debris on the bottom of the lake. Algae in the lake increased, and oxygen levels decreased. The surface area of the gills of some cichlid species has increased in just over 20 years.

• A. Increased gill surface area has allowed the cichlids to change their diet and avoid competing with the Nile perch.

• B. Increased gill surface area has allowed the cichlids to better absorb the limited oxygen supply in the water.

• C. Increased gill surface area has allowed the cichlids to be camouflaged and avoid being eaten by the Nile perch.

• D. Increased gill surface area has allowed the cichlids to leave Lake Victoria and establish populations in nearby bodies of water.

Answer explanation

Increased gill surface area helps cichlids absorb more oxygen from the water, which is crucial as oxygen levels decreased due to the Nile perch's dominance and the resulting ecological changes in Lake Victoria.

Three species of lizards of the genus Gallotia are found on the Canary Islands, a chain of seven volcanic islands off the coast of Africa. Which statement about the ancestry of the lizards from the genus Gallotia is best supported by this information?

• The common ancestor of the lizards first did not originate from Africa.

• The ancestors of each species came from different continents.

• The common ancestor of the lizards probably came from Africa.

• The ancestors of each species evolved in Spain.

Answer explanation

The lizards of the genus Gallotia are found on the Canary Islands, which are geographically closer to Africa. This suggests that their common ancestor likely originated from Africa, making the statement about African ancestry the best supported.

Which of the following statements gives the most likely explanation for the presence of two very similar species of squirrels living on opposite sides of the Grand Canyon?

• One squirrel traveled across the canyon and started a new population on the other side.

• One squirrel traveled across the canyon and interbred with a different population on the other side.

• Ancestral members of a single squirrel species were separated by the formation of the canyon.

• Members of two different squirrel species migrated from two different places to opposite sides of the canyon. 

Answer explanation

The correct choice explains that the canyon geographically separated members of a single squirrel species, leading to the development of two similar species on either side due to isolation.

A forest fire ignites in the Sam Houston State Forest and kills many members of a population of pigmy rattlesnakes. What would be the likely result for this species?

• Gene Flow

• Genetic Drift

Answer explanation

The forest fire caused a significant loss of pigmy rattlesnakes, leading to a random change in the population's genetic makeup. This is an example of genetic drift, where chance events affect allele frequencies, rather than gene flow.

This fossil turtle and this living hawk both have a structure in their neck called the atlas bone. What best explains why both species have an atlas bone?

• The turtle and hawk are different species, so they must not share an ancestor population. They inherited their atlas bone structure from separate ancestor populations

• The turtle and hawk both share the same ancestor population that had an atlas bone. They inherited this structure from the ancestor population.

• It is impossible to say. Fossils are very old; therefore, we cannot make observations of the turtle’s ancestors, and we cannot explain its body structures.

• All species have their own specific body structures, so it is a coincidence that this turtle and hawk each happen to have the atlas bone structure.

Answer explanation

The turtle and hawk both share a common ancestor that possessed the atlas bone. This structure was inherited from that ancestor, explaining its presence in both species despite their differences.

The diagram shows different vertebrate embryos. Which conclusion is supported by the diagram?

• A. Pigs evolved from reptiles.

• B. Reptiles evolved from birds.

• C. These organisms occupy the same niche.

• D. These organisms share a common ancestor.

Answer explanation

The diagram of vertebrate embryos shows similarities in early development stages, indicating that these organisms share a common ancestor. This supports choice D, as evolutionary relationships are often revealed through embryonic similarities.

Which species’ DNA is most similar to the DNA of the toothed whale? 

• Hippopotamus 

• Baleen Whale

• Grazing Mammals

• Camels

Answer explanation

The DNA of toothed whales is most similar to that of baleen whales because both belong to the cetacean group, sharing a more recent common ancestor compared to other mammals like hippos or camels.

Two organisms that are closely related would have

• very similar DNA sequence

• exactly the same DNA sequences

• no proteins in common

• completely different DNA sequence

Answer explanation

Two closely related organisms share a common ancestor, leading to very similar DNA sequences. They may not have exactly the same sequences due to mutations, but their genetic material will be more alike than that of unrelated organisms.

What is the primary mechanism by which natural selection operates?

• Random mutation

• Survival of the fittest

• Genetic drift

• Artificial selection

Answer explanation

Natural selection primarily operates through 'survival of the fittest', where individuals best adapted to their environment are more likely to survive and reproduce, passing on advantageous traits to future generations.