Theories of Organic Evolution Questions and Answers

Answer: B

Human evolution differs because humankind is a social and cultural species.

The passage says that among many animals the stock selected by nature breeds and continues the species, but Homo sapiens is a social and cultural species whose survival depends on culture.

Being a higher animal and nature selecting the stock are not what sets humans apart, and the passage nowhere calls unproductive people a burden, so the other options are wrong.

Answer: B

The difference is that individuals who do not reproduce also have a great role in survival.

The passage states that in our society all members contribute to the survival of the species, even if they bear no children, and that those who do not reproduce contribute more at present because of overpopulation.

The other options contradict the passage: breeding alone does not decide survival, overpopulation is called a threat, and specialization is said to increase contributions, not harm them.

Answer: A

The comparison is that infertile bees contribute to the survival of the colony.

The passage compares infertile worker bees, who make an essential contribution to the colony, with human beings who bear no children but still contribute to society.

The statement that only fertile bees contribute is false, and the passage says nothing to equate the roles of bees and humans or their population growth.

Answer: D

The greatest threat is over population.

The passage says that the stress of overdense populations is the greatest threat to human survival.

A changing environment, lack of knowledge and lack of adaptation are all mentioned as concerns, but the passage does not call any of them the greatest threat.

The question asks for the greatest threat, so read for the superlative: the passage uses the word greatest only for the stress of overdense populations, and a quick scan of the passage for that word finds the answer.

Answer: A

The vicious circle is increase in population and adaptation, then depletion of resources, then further adaptation.

The passage says new adaptations increase population, greater densities need further adaptations, and new adaptations deplete resources, which again requires further adaptation. Option A follows that chain.

The other options leave out the adaptation step or reorder the links, so they do not match the loop in the passage.

Answer: B

The process of evolution is a change in the genetic composition of a population over generations. Evolution in the biological sense is measured as a shift in gene (allele) frequencies, brought about by mutation, selection, drift and gene flow, so it is by definition a change, and it is carried by populations rather than by individuals.

Option A states the opposite of the definition. Option C is wrong because evolution is a dynamic process, never a static one. Option D is wrong because mutation is one of the main sources of new genetic variation on which evolution works.

Answer: B

The DNA molecule is a double helix: two polynucleotide strands wound around each other and held together by hydrogen bonds between the base pairs, as described by Watson and Crick in 1953.

A single helix is the form of most RNA, and a triple helix is an unusual structure found only in special conditions, not the DNA molecule in general, so only the double helix is correct.

Its two strands run in opposite directions (antiparallel), and adenine pairs with thymine and guanine with cytosine, which lets the molecule copy itself accurately when a cell divides.

Answer: D

Natural selection accounts for change over a period of time, for the progressive adaptation of organisms to their environment, and for the production of differences recognised by systematics, since selection acting on varying populations leads to adaptation and to the divergence that produces new species.

Each of the first three is true of selection, so the answer is 'All of the above'.

Natural selection works on the variation that already exists in a population. Individuals with traits that suit the environment leave more offspring, so adaptations build up, and when populations diverge the differences are the ones that taxonomists use to name species.

Answer: B

The name Pithecanthropus was given by the German biologist Ernst Haeckel as a hypothetical missing link, and Eugene Dubois, who found the Java fossil in 1891, used the name Pithecanthropus erectus. Among the options the person who named the fossil Pithecanthropus is Dubois.

Howells, Hooton and Haeckel are not credited with naming the Java fossil.

Dubois discovered the skullcap and femur at Trinil on Java in 1891 and 1892. The fossil was later reclassified as Homo erectus, and the name Pithecanthropus is now historical.

Answer: A

Assertion (A) is correct: in a population at genetic equilibrium (Hardy-Weinberg), gene frequencies and genotype frequencies stay constant from one generation to the next.

Reason (R) is false: equilibrium results from the absence of microevolutionary forces (mutation, selection, drift, gene flow and non-random mating). If those forces were present, the frequencies would change. So (A) is correct but (R) is false.

In such a population only the Hardy-Weinberg conditions hold: a large population, random mating, and no mutation, migration, selection or drift. The reason, as printed, gets this the wrong way round.