Starting Population Count
Spine Density
Spine Density
3. Cacti with very few spines tend to be eaten by animals, and cacti
with many spines tend to be preferred by parasitic insects. This
causes cacti with an average number of spines to be preferred. How
would you explain this?
A. This is an example of a stabilizing selection in which the
intermediate form of a trait is advantageous compared to the
extreme forms of the trait.
B. This is an example of bidirectional selection in which
evolutionary pressures from multiple sources encourage an
► organism to adapt.
C. This is an example of a disruptive selection in which the
population of cacti is divided and well defined.
D. This is an example of directional selection in which one end of
the bell curve is better adapted to its environment than the other
end.

background.  flavors from the mother’s diet during pregnancy are transmitted to amniotic fluid and swallowed by the fetus. consequently, the types of food eaten by women during pregnancy and, hence, the flavor principles of their culture may be experienced by the infants before their first exposure to solid foods. some of these same flavors will later be experienced by infants in breast milk, a liquid that, like amniotic fluid, comprises flavors that directly reflect the foods, spices, and beverages eaten by the mother. the present study tested the hypothesis that experience with a flavor in amniotic fluid or breast milk modifies the infants’ acceptance and enjoyment of similarly flavored foods at weaning.

methods.  pregnant women who planned on breast-feeding their infants were randomly assigned to 1 of 3 groups. the women consumed either 300 ml of carrot juice or water for 4 days per week for 3 consecutive weeks during the last trimester of pregnancy and then again during the first 2 months of lactation. the mothers in 1 group drank carrot juice during pregnancy and water during lactation; mothers in a second group drank water during pregnancy and carrot juice during lactation, whereas those in the control group drank water during both pregnancy and lactation. approximately 4 weeks after the mothers began complementing their infants’ diet with cereal and before the infants had ever been fed foods or juices containing the flavor of carrots, the infants were videotaped as they fed, in counterbalanced order, cereal prepared with water during 1 test session and cereal prepared with carrot juice during another. immediately after each session, the mothers rated their infants’ enjoyment of the food on a 9-point scale.