With the approach of Valentine's Day, love gurus, relationship mavens and infidelity experts (is that the same as an infidelity researcher, or is it someone who cheats on their spouse without getting caught?) take to the airwaves to tell you how to evaluate your relationship and determine the faithfulness of your partner.
While human relationships have existed for countless generations, biological research on what makes them happen has been around for a much shorter time.
The past few years have yielded a great deal of information on what makes men and women get together -- or stay apart.
First, however, a warning: A lot of the biology behind human relationships developed in eras when mating was much different than it was now, so natural instinct may not match the best decisions.
While people may once have been most worried about passing on their genes, they may need to be more worried with keeping their spouses happy now.
So while many of these nuances of human relationships may seem to justify infidelity, they might also explain why you have feelings that don't mesh with what you know to be best here in the 21st century.
As we take a look at five ways your body gives you relationship signals: don't worry too much if your ideas on relationships and the ideas here don't completely mesh. Genetics aren't destiny in life when it comes to disease, and they aren't destiny in relationships either.
Martie Haselton, a psychology researcher at the University of California Los Angeles, has done a number of studies on how ovulation affects women's behavior.
It seems that right before they are most likely to get pregnant, women with less sexually attractive partners find themselves tempted to cheat on their partners.
"We don't have unfaithful behavior in our studies because the frequency of actual cheating is pretty low," said Haselton. "What we asked them is who they notice, who they flirt with, who they are attracted to, and who their sexual desire is actually focused on."
What her research and other research in the area has shown, said Haselton, is that while we may look at how females in other species go through heat when they are prepared to mate, "there is something similar to that going on in humans."
The reason for this, she explains, is that there is a high cost in carrying a child for nine months and then breastfeeding them, and so a woman in earlier times would have wanted to ensure that the child had the best genetic material possible.
"A woman had only so many offspring and it was important for her to choose the best genetic father for all of her offspring," Haselton said.
She said her hypothesis may seem controversial because it implies that unattractive men are not good choices as mating partners. But she notes that changing times have made what is important in a partner change, and evolution in desires hasn't necessarily kept up.
"When cast in that light, this kind of information can be empowering to women as they navigate…through these situations," said Haselton.
"What matters most in the modern environment is not just basic survival, because most people have that down, but quality of emotional life."
She noted that a man who will help raise children is probably more important for ultimate happiness than if mom had strayed with a more attractive neighbor.