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The evolution of quasar clustering is investigated with a new sample of 388quasars with 0.3<z<=2.2, B<=20.5 and Mb<-23, selected over an area of 24.6 sq.deg. in the South Galactic Pole. Assuming a two-point correlation function ofthe form xi(r) = (r/r_o)^-1.8, we detect clustering with r_0=6.2 +/- 1.6 h^-1comoving Mpc at an average redshift of z=1.3. We find a 2 sigma significantincrease of the quasar clustering between z=0.95 and z=1.8, independent of thequasar absolute magnitude and inconsistent with recent evidence on theevolution of galaxy clustering. If other quasar samples are added (resulting ina total data-set of 737 quasars) the increase of the quasar clustering is stillfavoured although it becomes less significant. We find epsilon=-2.5.Evolutionary parameters epsilon>0.0 are excluded at a 0.3% probability level,to be compared with epsilon=0.8 found for galaxies. The observed clusteringproperties appear qualitatively consistent with a scenario of Omega=1 CDM inwhich a) the difference between the quasar and the galaxy clustering can beexplained as a difference in the effective bias and redshift distributions, andb) the quasars, with a lifetime of t~10^8 yr, sparsely sample halos of massgreater than M_min~10^12-10^13 h^-1 M_sun. We discuss also the possibility thatthe observed change in the quasar clustering is due to an increase in thefraction of early-type galaxies as quasar hosts at high z.Comment: 8 pages including 2 eps figures, LaTeX (AAS v4.0), ApJ in pres

Quasar Clustering: Evidence for an Increase with Redshift and Implications for the Nature of Active Galactic Nuclei