As humans societies have evolved from hunter-gatherers into civilized societies, there have been substantial changes in relations between people, with perhaps one of a few remaining biological constants being that both adult women and men must have sexual intercourse for human procreation to happen.

Humans have been compared to other species in terms of sexual behavior.

One factor behind the substantial growth among younger adults is their use of mobile dating apps.

Neurobiologist Robert Sapolsky constructed a reproductive spectrum with opposite poles being tournament species, in which males compete fiercely for reproductive privileges with females, and pair bond arrangements, in which a male and female will bond for life.

These species-particular behavior patterns provide a context for aspects of human reproduction, including dating.

Online dating has jumped among adults under age 25 as well as those in their late 50s and early 60s.

The share of 18- to 24-year-olds who use online dating has roughly tripled from 10% in 2013 to 27% today.

Despite the wealth of digital tools that allow people to search for potential partners, and even as one-in-ten Americans are now using one of the many online dating platforms, the vast majority of relationships still begin offline.

Even among Americans who have been with their spouse or partner for five years or less, fully 88% say that they met their partner offline–without the help of a dating site. Two thirds of online daters—66%—tell us that they have gone on a date with someone they met through a dating site or dating app.That is a substantial increase from the 43% of online daters who had actually progressed to the date stage when we first asked this question in 2005.With the use of modern technology, people can date via telephone or computer or meet in person.Dating may also involve two or more people who have already decided that they share romantic or sexual feelings toward each other.Today, nearly half of the public knows someone who uses online dating or who has met a spouse or partner via online dating – and attitudes toward online dating have grown progressively more positive.