The term you want to search for is "phytoestrogens". From wikipedia: "It has been hypothesized that plants use a phytoestrogen as part of their natural defence

The term you want to search for is "phytoestrogens". From wikipedia: "It has been hypothesized that plants use a phytoestrogen as part of their natural defence against the overpopulation of herbivore animals by controlling female fertility.[3][4]" Though wikipedia also says: "These compounds in plants are an important part of their defense system, mainly against fungi.[19]" So it could be that plants are principally targeting fungi for the most part, and just serendipitously targeting animals as well.