Organic Evolution Questions and Answers

Answer: B

The false statement is that genetic drift can lead to richness of genetic variation within populations.

Drift is random change in allele frequencies from one generation to the next because only a sample of gametes founds each generation. Its long-run effect is to lose alleles, as some drift to fixation and others to loss, so variation within a population falls.

The other three statements are true. Allele frequencies do change at random under drift. Because drift ignores fitness, a harmful allele can become fixed by chance. And the size of the random fluctuation scales inversely with population size, so drift is strongest in small populations, as in bottlenecks and founder events.

Answer: D

The component absent from Oparin's primitive atmosphere is oxygen.

Oparin, and Haldane independently, proposed that the early earth had a reducing atmosphere of methane, ammonia, hydrogen and water vapour, with no free oxygen. That absence mattered: free oxygen would have oxidised and broken down the organic molecules formed by lightning and ultraviolet radiation, so they could not have accumulated into a 'primordial soup'.

Methane, hydrogen and water are all part of the proposed mixture, and the same gases were used in the Miller-Urey experiment of 1953 that tested the idea. Free oxygen appeared only later, from photosynthesis by cyanobacteria.

Answer: C

Coacervates were formed by polymerization and aggregation.

In Oparin's scheme, simple organic molecules in the primordial waters first polymerised into larger molecules such as polypeptides and polysaccharides. These colloidal polymers then aggregated into droplets, the coacervates, separated from the surrounding water by a boundary and able to concentrate substances from it.

DNA was not part of the coacervate stage, which is pictured as preceding genetic material. Radiation and heat are energy sources that drove the synthesis of the small molecules, not the process that formed the droplets themselves.

Answer: B

A hybrid zone is a region where genetically distinct populations meet and interbreed to some extent.

Hybrid zones form where two diverged populations or incipient species come into contact, mate and produce hybrids, as in the narrow zones between fire-bellied and yellow-bellied toads in Europe. Studying what happens there, reinforcement, fusion or stability, shows how reproductive barriers evolve.

'Hybrids can develop' is too vague, since hybrids may arise anywhere. Populations that cannot interbreed produce no hybrids, so they do not form a hybrid zone. Populations of one region exchanging genes is ordinary gene flow, not a zone of contact between distinct populations.

Answer: C

Groups derived from more than one ancestor are polyphyletic.

A polyphyletic group gathers organisms from different ancestral lineages without their common ancestor, usually on a similarity that evolved independently. Grouping birds and bats together as 'flying vertebrates' is an example, since flight arose separately in each.

A monophyletic group (clade) contains one ancestor and all of its descendants. A paraphyletic group has one common ancestor but leaves out some descendants, as 'reptiles' do when birds are excluded. 'Heterophyletic' is not a standard term in systematics.

Answer: A

Weismann proposed the theory of continuity of germplasm.

August Weismann argued in the 1880s that the body is made of two kinds of tissue: the germplasm of the reproductive cells, which passes unbroken from generation to generation, and the somatoplasm of the body, which dies with the individual. Changes to the body therefore cannot be passed to offspring, a direct challenge to Lamarck's inheritance of acquired characters. He tested it by cutting the tails of mice over many generations; the offspring still had normal tails.

Continuity of protoplasm, plasma cells or cytoplasm is not his theory.

Answer: C

The process is Genetic drift.

Genetic drift is change in allele frequency caused by chance in which gametes and individuals happen to reproduce. Because it is random, an allele can drift to fixation or be lost altogether, and every loss reduces genetic variation. The effect is strongest in small populations, and bottlenecks and founder events are dramatic cases of it.

Gene flow brings alleles in from other populations and usually increases variation. Recombination shuffles existing alleles into new combinations rather than changing their frequency by chance. 'Spontaneous selection' is not a recognised evolutionary process, and selection in general is not random: it changes allele frequencies according to fitness.

Answer: B

The change is seen in the step Fishes to Amphibia.

A fish has a single, series circulation: the two-chambered heart pumps deoxygenated blood to the gills, and the blood passes on from there to the body before returning to the heart. In amphibians, with the move to lungs, a pulmonary circuit appears: two atria receive oxygenated blood from the lungs and deoxygenated blood from the body, so blood passes through the heart twice per circuit, in parallel pulmonary and systemic loops.

Agnathans and fishes share the series pattern, so that step shows no such change. Reptiles, birds and mammals refine a double circulation that already exists in amphibians, separating the ventricle partly or completely, rather than introducing it.

Answer: A

The statement is a belief and does not fall within the scope of experimental science.

A scientific hypothesis must make predictions that observations or experiments could show to be false. Special creation of each species by a supernatural act makes no such testable prediction, since any observation can be attributed to the creator's choice, so it lies outside experimental science.

A natural law describes a regularity that has been repeatedly observed, such as the law of independent assortment; a testable hypothesis is a falsifiable explanation; and a theory, such as the theory of evolution by natural selection, is a broad, well-tested explanatory framework. The creation statement is none of these.

Answer: D

Darwin's finches are an example of Adaptive radiation.

A single ancestral finch species from the South American mainland colonised the Galapagos and diversified into more than a dozen species. On different islands and in different niches, beaks evolved for crushing seeds, probing cactus flowers, catching insects or using tools. The rapid divergence of one lineage into many forms adapted to different ways of life is adaptive radiation.

Homology is shared structure inherited from a common ancestor and does not by itself describe diversification. Convergence is the evolution of similar traits in unrelated lineages, and parallelism similar changes in related but separate lineages; here one lineage has diverged, which is the opposite pattern.