At age 6, gender differences in growth are

John Harold Johnson Jr.'s death from sickle-cell anemia

a. resulted from a dominant gene. b. is related to the anti-malarial effects of sickle cells in ancestral populations. c. occurred because of the impoverished environment in which he grew up. d. is an example of what can happen when an individual has a high mutation rate. e. was caused by a bout of malaria in early childhood.

Helmholtz abandoned his attempt to measure the speed of a person's reaction to physical

stimuli because a. there was too much individual variability. b. the testing procedure raised ethical issues. c. the Church objected to the study of the human mind. d. self reports proved more reliable. e. he lost his financial backing.