  We re-examine the Fall & Efstathiou (1980) scenario for galaxy formation,
including the dark halo gravitational reaction to the formation of the baryon
disk, as well as continuous variations in the intrinsic halo density profile.
The recently published rotation curves of LSB and dwarf galaxies together with
previously known scaling relations provide sufficient information on the
present day structure of late type disk galaxies to invert the problem. By
requiring that the models reproduce all the observational restrictions we can
fully constrain the initial conditions of galaxy formation, with a minimum of
assumptions, in particular without the need to specify a CDM halo profile. This
allows one to solve for all the initial conditions, in terms of the halo
density profile, the baryon fraction and the total angular momentum. We find
that a unique initial halo shape is sufficient to accurately reproduce the
rotation curves of both LSB and normal late type spiral galaxies. This unique
halo profile differs substantially from that found in standard CDM models
(Navarro, Frenk & White 1996). A galactic baryon fraction of 0.065 is found.
The initial value of the dimensionless angular momentum is seen to be the
principal discriminator between the galaxy classes we examine. The present day
scalings between structural parameters are seen to originate in the initial
conditions.
