The evidence is in - Americans born in the '80s and '90s are less likely to be having sex than their parents who were born in the '60s and '70s.

In fact, kids today are having less sex than any other generation since the 1920s – a time when 5 percent of the global population had been killed off by the Spanish flu.

Although it goes against the stereotypes of millennials having easy access to sex from apps like Tinder, honestly… we probably should have seen the signs.

Pokémon Go is now way more popular then Tinder, and teen pregnancy rates are dropping every year. Combine that with easy access to porn and young people living at home for longer, and the results of this study start to make a bit more sense.

"This generation appears to be waiting longer to have sex, with an increasing minority apparently waiting until their early twenties or later," said lead author Jean Twenge from San Diego State University.

"It's good news for sexual and emotional health if teens are waiting until they are ready. But if young adults forgo sex completely, they may be missing out on some of the advantages of an adult romantic relationship."

The study looked at 26,707 American adults, and asked them to state how many sexual partners they'd had between the ages of 18 and 24.

Millennials born in the '90s were found to be twice as likely as those born in the '60s to say they had no sexual partners at all within that timeframe (15 percent of millennials to only 6 percent of Gen Xs).

"Online dating apps should, in theory, help millennials find sexual partners more easily," said Twenge. "However, technology may have the opposite effect if young people are spending so much time online that they interact less in person, and thus don't have sex."

And here's the real kicker: since the mid-century right up until millennials grew up, the amount of sexual partners young people were hooking up with was on the rise. Now we have to go back all the way to the early 1920s to see the same low hook-up levels that we see today.

"Americans born early in the 20th century also showed elevated rates of adult sexual inactivity. This could be due to the stricter adherence to mores around sex and marriage in these cohorts," the researchers report, adding that the end of WWI and Spanish flu outbreak might also have had something to do with it.

So not only do millennials have less sexual partners than our parents did, but we've started a whole new trend in having less sex. It's actually kind of impressive.

"This is really about this generation of young American adults and not the time period in which they are living," said one of the researchers, Ryne Sherman. "This has very little to do with changing norms about sexual behaviour; the generations are just different and it has everything to do with them."

Although there's likely a whole host of reasons for why millennials are having less sex, those purity rings and religious beliefs don't seem to come into it, with religiousness reportedly also on the decline in American young people.

Unfortunately, this study can't give us any concrete reasons for why young people are sleeping around less, but we're putting our money on Pokémon Go, and the myriad other things we have to do instead. Considering only 69 percent of straight sexual encounters result in orgasms for women… who's got the time?

The study was published in Archives of Sexual Behavior.