There is accumulating observational evidence suggesting that damped Ly \alpha absorption systems systems are the progenitors of present-day spiral galaxies .
We use the observed properties of these systems to place constraints on the history of star formation in galactic disks , and on cosmological theories of structure formation in the universe .
We show that the observed increase in \Omega _ { HI } contributed by damped Ly \alpha systems at high redshift implies that star formation must have been considerably less efficient in the past .
We construct a model in which gas is converted into stars with an efficiency that increases with time , and we show that this model can reproduce most of the observed properties of damped Ly \alpha systems , including the observed distribution of column densities .
We also show that the data can constrain cosmological models in which structure forms at late epochs .
A mixed dark matter ( MDM ) model with \Omega _ { \nu } = 0.3 is unable to reproduce the mass densities of cold gas seen at high redshift , even in the absence of any star formation .
We show that at redshifts greater than 3 , this model predicts that the total baryonic mass contained in dark matter halos with circular velocities V _ { c } > 35 km s ^ { -1 } is less than the observed mass of HI in damped systems .
At these redshifts , the photo-ionizing background would prevent gas from dissipating and collapsing to form high column density systems in halos smaller than 35 km s ^ { -1 } .
MDM models are thus ruled out by the observations .