Just as the biological needs are based on the survival of the individual, so the sociological needs are based on the survival of the species. Mother Nature loads Jack and Jill not only with hunger and thirst drives so that each of them will survive as an individual, but with sex drives so that they will get together in order for our species to survive.

      Since we can survive without sex - unhappy organisms but still live ones - we tend to assume that the sex drive is less powerful than the hunger and thirst drives. However, Mother Nature is more concerned with the preservation of the species than of the individual (like most parents, she aspires to be a grandparent) and would thus provide a powerful drive as a means to this end.

      The sex drive is designed to ensure that Jack and Jill will not only get together for that delightful experience created to bribe us to procreate our species but that they will stay together to care for the resultant offspring during that long period of infant dependency. This caring mechanism is built into the child during this period of dependency so that the child will, in turn, take care of its child. Our co-operation with other people is based on this caring mechanism established within the family. Many modern evolutionary theorists argue that it is co-operation rather than competition that has made our puny species the King of the Jungle.