  We present a study of the host galaxies of AGN selected from the zCOSMOS
survey to establish if accretion onto supermassive black holes and star
formation are explicitly linked up to z~1. We identify 152 galaxies that harbor
AGN, based on XMM observations of 7543 galaxies (i<22.5). Star formation rates
(SFRs), including those weighted by stellar mass, are determined using the
[OII]3727 emission-line, corrected for an AGN contribution. We find that the
majority of AGN hosts have significant levels of star formation with a
distribution spanning ~1-100 Msun yr^-1. The close association between AGN
activity and star formation is further substantiated by an increase in the AGN
fraction with the youthfulness of their stars as indicated by the rest-frame
color (U-V) and spectral index Dn(4000); we demonstrate that mass-selection
alleviates an artifical peak falling in the transition region when using
luminosity-limited samples. We also find that the SFRs of AGN hosts evolve with
cosmic time in a manner that closely mirrors the overall galaxy population and
explains the low SFRs in AGNs (z<0.3) from the SDSS. We conclude that the
conditions most conducive for AGN activity are a massive host galaxy and a
large reservoir of gas. Furthermore, a direct correlation between mass
accretion rate onto SMBHs and SFR is shown to be weak although the average
ratio is constant with redshift, effectively shifting the evidence for a
co-evolution scenario in a statistical manner to smaller physical scales. Our
findings illustrate an intermittent scenario with an AGN lifetime substantially
shorter than that of star formation and underlying complexities regarding
fueling over vastly different physical scales yet to be determined [Abridged].
