It has been known for a long time that maleness in most mammals relates to aggressive behavior and a less nurturing tendency, compared to females. Humans are no exception to the above fact. The male sex hormones, more specifically testosterone has been blamed for such behavior. It has now been found that sex chromosomes also have a significant role in dictating male behavior.
Neuroscientists at the University of Virginia Health System have conducted experiments on mice models and have concluded that diversity in social behavior of males and females are indeed due to different genetic constitution of the male (one X chromosome and one Y chromosome) and female (two X chromosomes).
The researchers developed mice through genetic engineering techniques (transgenic mice, devoid of SRY gene) and studied the patterns of adult behavior, more specifically maternal behavior and aggression. Although sex chromosomes may not totally determine the level of maternal behavior, it does play an important role. The results of this study can be found in the February issue of the Journal of Neuroscience.
The SRY gene, the gene that determines if a growing embryo should develop into a male or female formed the main focus of the study. The presence of SRY gene causes the primitive gonads to develop into testis (the male gland that produces sperms and male sex hormones). The gene is believed to be partially responsible for aggressive behavior.
Behavior pattern of mice (both parental and aggressive behavior) that contained either XY or XX chromosomes were compared to mice with or without the SRY gene that was placed in their territory. Gonadal male mice (with SRY gene) and female mice with SRY gene were found to display high level of aggressiveness compared to male and female mice without the SRY gene. In addition, male mice without SRY gene and female mice without SRY gene displayed high levels of maternal behavior (building nests/ picking up pups).
So far, it has been thought that only male sex hormone determined social aspect of male behavior. This study throws light on the fact that sex difference could be due to difference in genetic constitution of the male and female. With our improved understanding of genetics and human behavior, perhaps some day, it might be possible to alter the behavioral pattern of males and females through genetic manipulation.