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The majority of animals in the world are not monogamous with only around five percent, or 4,000 mammal species that practice this type of union. Due to the concept that monogamy might not be a natural process since most animals are focused on reproducing as many offspring as possible, studying why monogamy occurs in these select animals can be very enlightening. Two new research studies that were recently published have provided two more viable theories as to why mammals are monogamous.

In the first research study, the team looked at over 230 different primate species through generations. The researchers concluded that over time, men decided to stick with one female mate in order to prevent other unrelated males from killing their offspring. Since females cannot reproduce right after birth due to the fact that they need to nurse their offspring, other males will murder the newborns in order to speed up the process of reproduction with the female. Due to this risk, the researchers believe these primate males switched from being focused on expanding their genetic pool by impregnating numerous females to the need of protecting their young.

 "This is the first time that the theories for the evolution of monogamy have been systematically tested, conclusively showing that infanticide is the driver of monogamy," Christopher Opie, a research fellow in the Anthropology Department of University College London, said in a statement. "This brings to a close the long running debate about the origin of monogamy in primates." Opie's study was published in the Proceeding of the National Academy of Sciences (PNAS).

In the other study, researchers were quick to suggest that infanticide was not related to monogamy. The research team composed of Dieter Lukas and Tim Clutton-Brock from Cambridge University looked at around 2,500 mammals. Based from their observations, they believe that monogamy developed based on location and supply. They reasoned that males ended up picking one mate that they could confidently say was pregnant with their offspring because of a lack of resources. If they impregnated numerous females, they would not have the resources to fend off other men within the area and thus, the risk that they end up wasting energy to protect a female whose offspring belongs to another male is too high.

"It's a consequence of resource defense," Lukas stated.

Despite this finding, the researchers of the second study are not too convinced that humans are completely monogamous. Their study was published in the journal, Science. Researchers from both studies confidently believe that monogamy did not arise from the males' desire to rear children, which is another theory that has been presented before. Although both theories may make sense to a certain extent and are backed by some degree of evidence, determining the exact cause of monogamy in some animals is impossible