@mzazii, it is because this river of joy iko pahali inaenda inaleta furaha in women. It is an anti-depressant, eases stress.
'A study undertaken....showed that the women who were directly exposed to semen were less depressed. The researchers think this is because mood-altering hormones in semen are absorbed through the vagina. the results aren't a complete surprise because semen does contain several mood-altering hormones, including testosterone, oestrogen, follicle-stimulating hormone, luteinising hormone, prolactin and several different prostaglandins. Some of these have been detected in a women's blood within hours of exposure to semen..''
http://www.newscientist....s-an-antidepressant.html