Artificial evolution

In some biology simulations, you don't even need to store the location of each critter. Surprisingly enough, evolution simulations are often of this type.

Each critter is either male or female.
Each critter has it's own ratio of
  male to female offspring.
Each timestep:
    Select a male critter C1 at random
    Select a female critter C2 at random
    delete 2 random critters
    create 2 offspring from C1 and C2

When creating offspring from C1 and C2, one offspring inherits C1's male/female probability gene, the other inherits C2's, and they are male or female with their respective probabilities.

To provide a bit of variation, occasionally randomize a critter's male/female gene.

When you run this extremely simple simulation, the ratio of males to females in the population quickly approaches 50/50. The genepool also changes significantly, from a set of random ratios to a pool entirely filled with genes near 50/50.

This happens because of negative feedback. When one sex becomes more numerous, genes that produce more of the other sex gain an advantage at reproducing themselves, thus rebalancing the population.

So, sorry guys, all those sci-fi stories with races of space-babes whose populations are 7/8ths female just aren't possible. Unless, of course, they've got the genetics of a hive insect, in which case most of them won't be interested.