Lee Rannals for redOrbit.com — Your Universe Online
A new study says eating certain vegetables may influence hormone levels and behaviors like aggression and sexual activity in monkeys.
The research from the University of California, Berkeley is the first to observe the connection between plant-based estrogenic compounds and behavior in wild primates.
They found that the more leaves of Millettia dura the male red colobus monkeys ate, the higher their levels of estradiol and cortisol. Also, the team saw the altered hormone levels brought on more acts of aggression and sex.
“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,” study lead author Michael Wasserman, said in a statement. “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.”
The team followed a group of red colobus monkeys in Uganda’s Kibale National Park for 11 months, documenting what the primates ate. They focused on aggression for key behavioral observations, marking down the number of chases and fights, the frequency of mating and time spent grooming.
The team collected fecal samples once a week from each of 10 adult males in the group to assess changes in hormone levels. Over 407 samples were collected and analyzed for estradiol and cortisol levels.
They found seasonal variation in the consumption of estrogenic planets, making up 32.4 percent of the red colobus diet in any given week sometimes.
The higher the consumption of estrogenic plants, the higher the levels of estradiol and cortisol for the males, which are two steroid hormones important to reproduction and the stress response.
“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,” study co-author Katharine Milton, said in a statement. “This is particularly true when determining the influence of phytoestrogens on reproductive behavior, which is the whole keystone of natural selection.”
The researchers emphasized that estrogenic plant consumption is one of multiple factors influencing primate hormone levels and behavior. They also noted the tendency for certain behaviors to occur can be affected by complex interactions between endogenous hormones and phytoestrogens.
Previous research found eating estrogenic plants could disrupt fertility and affect behavior in animals like rodents, monkeys and sheep. Effects of phytoestrogen consumption in other studies have included more aggression, less body contact, more isolation, higher anxiety and impaired reproduction.
The team is now examining the relationship between phytoestrogens and other primate species, including the chimpanzee, which is the human’s closest-living relative.
“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,” Wasserman said in the statement.
The team noted the red colobus diet contains a higher percentage of leaves, while the diet of chimpanzees, other apes and human ancestors consists primarily of fruits.
“If phytoestrogens make up a significant proportion of a fruit-eating primate´s diet, and that consumption has similar physiological and behavioral effects as those observed in the red colobus, then estrogenic plants likely played an important role in human evolution,” said Wasserman. “After studying the effects of phytoestrogens in apes and fruit-eating primates, we can then get a better sense of how these estrogenic compounds may influence human health and behavior.”
The study was published in the current issue of the journal Hormones and Behaviors.
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