[uis]

Anyway even all girls anime is genre but that doesn't mean man not exist in that anime.

You can see some male in background or just one male become supportive chara or just parent/father exist or male is antagonist.

You can see this example in Yuru Yuri and Koihime Musou.

That also exist anime without male but some mechanism explained like baby from the sky or female pregnant after drink sacred river water.

You can see this example in Sengoku Otome.