The Penna model for biological ageing on a lattice: spatial consequences of child-care

We introduce a square lattice into the Penna bit-string model for biologica l ageing and study the evolution of the spatial distribution of the populat ion considering different strategies of child-care. Two of the strategies a re related to the movements of a whole family on the lattice: in one case t he mother cannot move if she has any child younger than a given age, and in the other case if she moves, she brings these young children with her. A s tronger condition has also been added to the second case, considering that young children die with a higher probability if their mothers die, this pro bability decreasing with age. We show that a highly non uniform occupation can be obtained when child-care is considered, even for an uniform initial occupation per site. We also compare the standard survival rate of the mode l with that obtained when the spacial lattice is considered (without any ki nd of child-care).