Medical discoveries such as antibiotics and vaccinations have indirectly contributed to the sharp rise in human population.

Antibiotics and vaccines have greatly reduced deaths from infectious diseases, so the DEATH RATE has fallen sharply and life expectancy has risen. The BIRTH RATE, however, has remained high, and the widening gap between births and deaths is what produces the rapid growth in population.

The word INDIRECTLY in the question is the clue: medicine does not cause more babies to be born, it causes fewer people to die.

THE CENTRAL POINT of this chapter: a population explosion results from a FALLING DEATH RATE against a high birth rate, not from a rising birth rate. Smallpox has been eradicated altogether, and diseases that once killed millions are now preventable.

That is also why population programmes work on the BIRTH rate — nobody wishes to reverse the fall in deaths.