Evolution of galaxies - One-zone model with a birth-rate stellar function depending on gas density and temperature

'Comoving' closed one-zone models with a birth-rate stellar function depending on gas density and temperature are considered as a zeroth order approximation to thermochemical evolution of galaxies. The models are made first to expand with the universe after recombination, and then the ensuing phases of violent relaxation and rapid contraction are simulated. Based on certain boundary conditions, such as the time-independence of the relative metal abundances, numerical computations performed up to 12 Gy reproduce a whole class of theoretical models, ranging between the limiting cases of a density-dependent birth rate (Schmidt's law) and a temperature-dependent birth rate. The proposed 'universal' birth rate stellar function is consistent with both a dynamical history starting from the initial expansion of protogalaxies, and a morphological sequence which is described (for any given mass) by the amount of angular momentum, at least for what concerns spiral types.