However, one particularity of the human species is that pair bonds are often formed without necessarily having the intention of reproduction.
In modern times, emphasis on the institution of marriage, generally described as a male-female bond, has obscured pair bonds formed by same-sex and transsexual couples, and that many heterosexual couples also bond for life without offspring, or that often pairs that do have offspring separate.
Cars extended the range of dating as well as enabled back-seat sexual exploration.
In the mid-twentieth century, the advent of birth control as well as safer procedures for abortion changed the equation considerably, and there was less pressure to marry as a means for satisfying sexual urges.
New types of relationships formed; it was possible for people to live together without marrying and without children.