Final answer:
The birthrate in America grew by nearly 50% between 1935 and 1964 due to the 'baby boom', a period of significant increase in births post-World War II, influenced by various social and economic factors.
Step-by-step explanation:
Between 1935 and 1964, the birthrate in America grew significantly due to a period known as the "baby boom". This period began after World War II and lasted until around 1964. The baby boom was characterized by a dramatic increase in births, resulting from the return of military personnel, the desire of young Americans to start families, and the economic security that allowed established couples to have more children. An estimated 80 million Americans were born during the baby boom years, greatly influencing the demographic makeup of the country.
There was a noticeable bulge in the population pyramid during these years, indicating that birthrates had surged. The baby boom led to a growth in the birthrate of nearly 50%, which stands as a notable event in America's demographic history.