It was the year 44,444.

Slightly over a century ago Humanity's scouts finally found a sapient alien race that had survived the immediate aftermath of inventing the atomic bomb, and it turned out that we were similar enough in our thinking to not only communicate, but socialize.

Thing was there were a few small issues...

Roughly four centuries ago the human Y chromosome finally became so damaged and degraded that no amount of genetic engineering could allow us to perpetuate the male half of the species. It had been a crew of "Straight-Jackets" scouring the fringes of known space for a rumored lost colony where male humans survived that had made first contact, and the Golglana had an interesting gender imbalance problem of thier own, for the past two hundred years thier males were not being eaten during mating for the first time in history!

Things got weirder, the males who had mated and lived found human women very attractive: apparently we "smell goooood!" Some of the crew of the "Archangel Michelle" were desperate enough for ANY man that they tried it...

And LIKED IT: liked it A LOT...

It turned out that our two species, though very different in gross physiological terms, are quite similar genetically, biologicaly, and mentally. There are enough differences between us that we can't live on the same planets comfortably over the long term, in fact we need a different enough atmospheric mix that we can only breathe the same air for about an hour without respiration equipment before we start feeling woozy, but it's enough that we can work the ships together if we have compartmentalized quarters, and so, after a few years of negotiations, the Galactic Union of Human Worlds became The Galactic Union of Civilized Races.

Golglana scout ships went out looking for colony worlds, and a lot of "Straight-Jacket" women found themselves dating alien men...