Most Starlings Produce Four to Five Eggs in Each Clutch.
Most starlings produce four to five eggs in each clutch. Starlings producing fewer or more than this have reduced fitness. Which of the following terms best describes this situation?
A) directional selection
B) stabilising selection
C) disruptive selection
D) sexual selection
When imbalances occur in the sex ratio of sexual species that have two sexes (that is, other than a 50:50 ratio), the members of the minority sex often receive a greater proportion of care and resources from parents than do the offspring of the majority sex. This is most clearly an example of ________.
A) sexual selection
B) balancing selection
C) stabilising selection
D) frequency-dependent selection
A proficient engineer can easily design skeletal structures that are more functional than those currently found in the forelimbs of such diverse mammals as horses, whales, and bats. The actual forelimbs of these mammals do not seem to be optimally arranged because ________.
A) natural selection has not had sufficient time to create the optimal design in each case, but will do so given enough time
B) in many cases, phenotype is determined by genotype and the environment
C) though we may not consider the fit between the current skeletal arrangements and their functions excellent, we should not doubt that natural selection ultimately produces the best design
D) natural selection is generally limited to modifying structures that were present in previous generations and in previous species
Anopheles mosquitoes, which carry the malaria parasite, cannot live above elevations of 1,800 metres. In addition, oxygen availability decreases with higher altitude. Consider a hypothetical human population that is adapted to life on the slopes of Mt. Kilimanjaro in Tanzania, a country in equatorial Africa. Mt. Kilimanjaro's base is about 800 metres above sea level and its peak is 5,895 metres above sea level. If the incidence of the sickle-cell allele in the population is plotted against altitude (metres above sea level), which of the following distributions is most likely, assuming little migration of people up or down the mountain?