For the first time, researchers found evidence that the consumption of plant-based estrogenic compounds, or phytoestrogens, likely played an important role in human evolution.
For 11 months, a research team studied a group of red colobus monkeys in Uganda, known to eat leaves from a tropical tree with estrogen-like compounds, called Millettia dura.
They found that the more the apes ate the leaves, the higher their levels of estradiol and cortisol – two steroid hormones influencing reproductive behavior. The altered hormone levels increased the frequency of mating and decreased the time spent grooming.
According to study lead author Michael Wasserman, the findings suggest that consuming phytoestrogens has been important in primate ecology and evolution.
“It’s one of the first studies done in a natural setting providing evidence that plant chemicals can directly affect a wild primate’s physiology and behavior by acting on the endocrine system,” says Wasserman, who conducted the research as a graduate student at University of California, Berkeley’s Department of Environmental Science, Policy and Management.
“By altering hormone levels and social behaviors important to reproduction and health, plants may have played a large role in the evolution of primate—including human—biology in ways that have been underappreciated.”
Phytoestrogens aren’t only part of a monkey’s diet, as they can also be found in soy and soy-based products. Millettia dura is a close relative of soy.
“With all of the concern today about phytoestrogen intake by humans through soy products, it is very useful to find out more about the exposure to such compounds in living primates and, by analogy, human ancestors,” says study co-author Katharine Milton.
“This is particularly true when determining the influence of phytoestrogens on reproductive behavior, which is the whole keystone of natural selection.”
To further explore the connection between estrogenic plant consumption and behavior in wild primates, the researchers are now examining its effects on other primate species, including our closest-living relative, the chimpanzee.
“Human ancestors took most of their diet from wild tropical plants, and our biology has changed little since this time, so similar relationships as those found here are expected to have occurred over our evolutionary history,” says Wasserman.
Wasserman, M., Chapman, C., Milton, K., Gogarten, J., Wittwer, D., & Ziegler, T. (2012). Estrogenic plant consumption predicts red colobus monkey (Procolobus rufomitratus) hormonal state and behavior Hormones and Behavior, 62 (5), 553-562 DOI: 10.1016/j.yhbeh.2012.09.005