At Thanksgiving dinner, your dad tells the old story about how your great-grandmother's longevity was related to a daily breakfast of coffee and grapefruit plus broccoli every night with dinner. No one else in your extended family lived to over 100 like she did, and your dad insists that this is because everyone else in the family has failed in their attempt to follow her diet plan. You speak up this Thanksgiving and offer your hypothesis that the dietary failure of the subsequent generations suggests that
A. your great-grandmother was a PTC-nontaster whereas everyone else in your family can taste PTC.
B. everyone else in the family is affected by balanced polymorphism, where they have evolved genes to be healthier during life no matter what they eat but also have a shortened lifespan.
C. natural selection has removed the genes that code for adherence to a dietary regime from the recent generations of your family.
D. changes in farming practices have adversely affected the quality and taste of coffee, grapefruit, and broccoli over the past few generations.
Answer: Your great-grandmother was a PTC-nontaster whereas everyone else in your family can taste PTC.