The world of Minecraft, according to its creator, is one that's completely devoid of either sex or gender.
Markus "Notch" Persson took time to officially clarify Minecraft's take on gender in a quick blog post on The World of Notch. When he was working on the project during its beginnings, he was asked what to call the "Minecraft Guy;" his response was "Steve."
Minecraft Steve, however, is not a male. He's not female, either. Why does this matter? The gender (or, perhaps, non-gender) of Minecraft Steve is relevant to the Minecraft experience because of the spirit of the adventure itself.
Here's Notch with a moment of clarity regarding Minecraft.
…Minecraft would be a game where gender isn't a gameplay element.
The human model is intended to represent a Human Being. Not a male Human Being or a female Human Being, but simply a Human Being. The blocky shape gives it a bit of a traditional masculine look, but adding a separate female mesh would just make it worse by having one specific model for female Human Beings and male ones. That would force players to make a decisions about gender in a game where gender doesn't even exist.
Notch goes on to explain that even the animals are genderless/sex-less. Any animal can breed with any other animal of the same species; there's no gender matching prerequisite involved in the process.
Minecraft is a blank slate. That regard goes for everything from building to exploration; apparently, it even goes for gender definition.
The only argument I can set forth regarding the absence of gender in the Minecraft universe is the presence of skins. Skins allow gender. Gameplay might not change with skins, but the physical presence of gender exists.
What say you, Minecraft fans?
[via The Word of Notch]