However, to many biologists it seemed unlikely until recently, that mating and sex could be a primordial and fundamental characteristic of eukaryotes. A principal reason for this view was that mating and sex appeared to be lacking in certain pathogenic protists whose ancestors branched off early from the eukaryotic family tree. However, several of these protists are now known to be capable of, or to recently have had, the capability for meiosis and hence mating. To cite one example, the common intestinal parasite "Giardia intestinalis" was once considered to be a descendant of a protist lineage that predated the emergence of meiosis and sex. However, "G. intestinalis" was recently found to have a core set of genes that function in meiosis and that are widely present among sexual eukaryotes. These results suggested that "G. intestinalis" is capable of meiosis and thus mating and sexual reproduction. Furthermore, direct evidence for meiotic recombination, indicative of mating and sexual reproduction, was also found in "G. intestinalis". Other protists for which evidence of mating and sexual reproduction has recently been described are parasitic protozoa of the genus "Leishmania", "Trichomonas vaginalis", and acanthamoeba.