It has been written that "the tao produced one, one produced two, two produced three, three produced the countless things." This does not fit very well with what I am about to say and should be ignored at best and removed from this post at worst.
Numerology has classically held that one is neither masculine nor feminine, but the Unity number; that two is feminine; that three is masculine and the number of the Father.
The Patriarchy has it that Man comes first, woman comes second. Third would be nonsensical crimethink.
As crimethink is butter to my bread, I would suggest that the first sex is neuter/spivak/eunuch/hermaphroditic/splu
It is worth noting that the yinyang was invented by Discordians, according to Discordians, and representing the feminine and masculine in this way is just another 23 gag.
The ancient Greeks (some of them) had it that mankind was first created as giant double things, which were divided into couples. The drive to mate/marry was seen under this gaze as the desire to reunite with one's soul's other half.
Those who tell the story of Eden have it that God produced Adam, from Adam was produced Eve, through Eve was produced Set, and Set fathered the Patriarchs of the Bible. "A man and a woman had a li'l baby, yes they did. There were three in the family, that's the magic number." Blind Melon was an Illuminist front.
*this part has been censored for y/our protection -- The Secret Chiefs*