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The human brain. Differences in male and female brain size are relative to body size. [83] Early research into the differences between male and female brains showed that male brains are, on average, larger than female brains. This research was frequently cited to support the assertion that women are less intelligent than men.
Bcl-2 is an antiapoptotic protein. The level of Bcl-2 in PD8 male rats is much higher than that in female rats of the same age, hence the number of apoptotic cells of MPNc in PD8 male rats is much lower than PD8 female rats. On the other hand, Bax, a proapoptotic protein, shows lower level in PD8 males than in PD8 females.
Female (left) and male (right) Argiope appensa, displaying typical sexual differences in spiders, with dramatically smaller males Hammock Spiders (Pityohyphantes sp.) courting. Female left and male right. Many arachnid groups exhibit sexual dimorphism, [45] but it is most widely studied in the spiders.
The ideas of differences between the male and female brains have circulated since the time of Ancient Greek philosophers around 850 BC. In 1854, German anatomist Emil Huschke discovered a size difference in the frontal lobe, where male frontal lobes are 1% larger than those of females. [6]
However, such sex differences are primarily limited to the anthropoid primates; most of the strepsirrhine primates (lemurs and lorises) and tarsiers are monomorphic. [2] Sexual dimorphism can manifest itself in many different forms. In male and female primates there are obvious physical difference such as body size or canine size.
Other published research explored differences between the cerebral cortex of male and female rats, the link between positive thinking and immune health, and the role of women in science. [ 2 ] [ 3 ] Early life and education
In some rodents, males are larger than females, while in others the reverse is true. Male-bias sexual dimorphism is typical for ground squirrels, kangaroo rats, solitary mole rats and pocket gophers; it likely developed due to sexual selection and greater male–male combat. Female-bias sexual dimorphism exists among chipmunks and jumping mice.
The original experiments with rats applied the following protocol: A male rat was placed into an enclosed large box with four or five female rats in heat. [13] He immediately began to mate with all the female rats repeatedly until he eventually became exhausted. [13] The females continued nudging and licking him, yet he did not respond. [13]