Are women of Mexican heritage more fertile than women of other decent?

No, Mexican and I would say, Mexican-American men are just plain hornier. I remember seeing an interview with an anglo woman who was a nymphomaniac. When asked if she had ever been satisfied by any man, she took a very long time to answer, and then finally said it was a latino man who couldn't get enough sex. She then described it as a parralell to boxing ("Look at how those guys fight, then just keep coming back at you!"). I would say that it's true.