It's a tough row to hoe. Primatology is not a mainstream academic discipline, and that means there are few tenure-track jobs. PhD's they produce. Some students opt for a PhD program under the impression that graduate school admission requirements are lower than those for medical school or law school. From what I've seen of applicants to IU, it's the other way around.
Competition is intense for the few grad school slots available.
It's also a long row to hoe. Before deciding to pursue a doctorate you should be very honest with yourself about your intellectual abilities, your work-ethic, your tolerance of poverty, and most of all your passion for primatology. If there is another career where you'd be just as fulfilled intellectually, choose it. I, for one, had no choice. I'm squeamish about prodding sick and injured people, so a career in medicine was unattractive.