Chimpanzees that are aggressive father more offspring, scientists announced on Thursday. A 17-year study of Tanzanian chimpanzees published in the scientific journal Current Biology concluded that males that acted aggressively towards females and sometimes attacked them physically, significantly improved their chances of producing babies with the females they bullied. Ian Gilby, an evolutionary anthropologist from Arizona State University said that this was definitely not a positive development.
Gilby further added that aggressive males in the chimpanzee community had a higher probability of producing offspring with females than males that were not as forceful. While the research was conducted on a genetically close species to human beings, scientists are cautious about drawing conclusions about the roots of sexual violence in humans. Gilby also concluded that in spite of differences, acknowledging the relative value of studying chimpanzee male on female aggression could prove valuable in understanding and perhaps stop the same types of behavior in human beings.
Scientists compiled detailed data by observing chimpanzees in Gombe National Park, Tanzania. Researchers analyzed fecal matter DNA to determine which chimpanzees had mated and the paternity of 31 infants conceived throughout the study from 1995 to 2011.
Ann Pusey, a Duke University evolutionary anthropologist said that female chimpanzees were intimidated by continuing aggression and would give in to aggressive males that could potentially father offspring. At times, fertile females would not mate with less violent males when an aggressive male was in the vicinity because they were afraid of reprisal. The anthropologist determined that females during their greatest level of fertility looked to mate with the same males that were aggressive towards them.
The violent actions exhibited by the males involved chasing, striking and biting that could leave the female wounded and on occasions, the male would charge and smash nearby vegetation. Mating was not immediate after the aggressive behavior, it was gradual bullying behavior over a period of two to three years that was especially successful in later assuring paternity.
Anthropologists said that the lineage of evolution for chimpanzees and humans diverged millions of years ago and that the reproduction for the two species is not the same. The analysis of the study results suggested that aggressive males are selected for in order to raise their success for fatherhood, which is the reason this type of aggression is observable in many populations of chimpanzees, stated Joseh Feldmen, a Duke University first author.
Researchers found that male chimpanzees directed unexpected amounts of aggression at females in their group, although previous studies of chimpanzee mating developed data against, as well as for, the practice of sexual aggression in wild populations of chimpanzees. They also noted that while male aggression during a female’s sexually receptive state resulted in increased mating, it did not necessarily lead to increased paternity. Conversely, males that were high-ranking and aggressive towards non-sexually receptive females had more offspring because of their bullying.
The final analysis of the study found that through extended periods of intimidation, males that had a high-ranking were able to positively influence their success for reproduction and increasing the spread of their own DNA. This particular study offered one the first examples of using DNA evidence to examine sexual aggression strategies in populations of social mammals.
By Gerald Sowell
Photo By TheBusyBrain – Flickr License