Despite relatively limited faculty (compared to other animals), human sense of smell is obviously important to our lives. Its diminishment affects appetite and general enjoyment of life. We each have our own scent signature and can tell our health condition by it. Humans can smell whether they are related to another person. This is part of the innate sense against incest.
Human smell develops in the womb. A few days after birth, an infant can recognize its mother by the scent of her nipples and underarms. The distinctive odor of siblings is well known by the age of 5 years.