How old are the extant lineages of Toxoplasma gondii? 
Most known isolates of Toxoplasma gondii belong to one of only three lineages, which are presumed to be clonal.  Three models have been proposed for the evolutionary relationship of these lineages to the other extant lineages: Model (a) proposing that all lineages are derived from a most recent common ancestor (MRCA) in the distant past, Model (b) that all lineages are derived from a MRCA in the very recent past, and Model (c) that the clonal lineages share a recent MRCA but are related to the other lineages only in the distant past.  Here, I test these models using DNA intron and coding-sequence data for loci at 14 genes, using three different methods to calculate the time of the MRCA.  All of the calculations agree that the MRCA of the clonal lineages was > 70% of the age of the MRCA of all lineages, thus favouring Model (a).  The MRCA may have existed approximately 150,000 years ago, with the clonal lineages expanding in prevalence approximately 10,000 years ago.