Our improved understanding of dark-matter halo statistics can be effectively <br />
used to extract useful physical information directly from the observed galaxy <br />
statistics commonly measured from large galaxy surveys, such as luminosity <br />
function and clustering properties (luminosity-dependent trend and overall shape) <br />
of galaxies. I will discuss a simple formalism to constrain the scaling laws between <br />
UV luminosity and halo mass (local gravity), and the typical duration of <br />
star-formation at z~4 and 5. From these results, possible dominant mechanisms <br />
responsible for star-formation activity in the majority of galaxies (L<L*) are<br />
discussed.