Hi gurus

how can I get Collection of specific Class?

I use inheriance: On Planet live Human. Humans are dividing to Men and Women.

class Planet{
   String name
   static hasMany = [ humans : Human ]
}

class Human{
    String name
    static belongsTo = [Planet]
}

class Man extends Human{
     int countOfCar
}

class Woman extends Human{
     int coutOfChildren  
}

now a neet to get only Collection of Man or Collection of Woman:

get all humans on planet is simple

all = Planet.get(1).humans

but what can I get only woman or men?
womenLivedOnMars = Planet.get(1).getOnlyWoman
menLivedOnJupiter = Planet.get(2).getOnlyMan

Thanks for your help
Tom