The effect of redshift on the observation of distant galaxies is briefly
discussed emphasizing the possible sources of bias in the interpretation of
high-z data. A general energetic criterion to assess physical self-consistency
of evolutionary population synthesis models is also proposed, for a more
appropriate use of this important tool to investigate distinctive properties of
primeval galaxies.Comment: 8 pages and 6 color figures. Invited talk at the conference "New
Quests in Stellar Astrophysics: The link between Stars and Cosmology", 26-30
March, 2001, Puerto Vallarta, Mexico, eds. M. Chavez et al., to be published
by Kluwe
