Sex differences in human physiology
Physiological sex differences include discrete features such as the respective male and female reproductive systems, as well as average differences between males and females including size and strength, bodily proportions, hair distribution, breast differentiation, voice pitch, and brain size and structure.
In some cases, for example, chromosomally female babies that have been exposed to high levels of androgens before birth can develop masculinized genitals by the time they are born.
[14][15] Although variations exist and there may be a degree of overlap between typically male or female traits,[14][15] the pelvis is the most dimorphic bone of the human skeleton and is therefore likely to be accurate when using it to ascertain a person's sex.
[17] This greater angle applies a larger portion of the gravitational or vertical load as valgus torque (rotational force against the knee).
[23] The following further generalizations have been made regarding male-female skeletal differences: Pubertal changes in males lead to a ten times increase in testosterone.
Males typically have larger tracheae and main bronchi and greater lung volume per body mass.
[46][47] The lighter skin in females helps their bodies synthesize more Vitamin D from sunlight and absorb more calcium, which is needed during pregnancy and lactation.
[49] In lighter-complected humans, male skin is visibly redder; this is due to greater blood volume rather than melanin.
[52][53] The differences in color are mainly caused by higher levels of melanin in the skin, hair and eyes in males.
[56] Another study found green eyes, which are a result of lower melanin levels, to be much more common in females than in males, at least by a factor of two.
[62] It is worth noting that between 1.7% and 4% of humans may be classified as intersex, which can mean (among other forms of variation) that one or more of the internal or external genitalia associated with their sex assignment is absent, different from the typical presentation, etc.
The release of this fluid is a product of the Skene's gland (female prostate), located within the walls of the urethra.
Thus during a lifetime males are able to father a significantly greater number of children than females can give birth to.
The most fertile female, according to the Guinness Book of World Records, was Valentina Vassilyev of Russia (1707–1782) who had 69 surviving children.
[68][69] Female physical experiences vary depending on external forces such as diet, marriage patterns, culture, and other aspects.
[70] More lactation in the lifetime of non-western females inhibits ovulation and extends the number of fertile years.
Paternal age effects in children include multiple sclerosis,[73] autism,[74] breast cancer[75] and schizophrenia,[76] as well as reduced intelligence.
Her record stood until Maria del Carmen Bousada de Lara gave birth to twin sons at Sant Pau Hospital in Barcelona, Spain on December 29, 2006, at the age of 67.
The degree of hemispheric asymmetry in males corresponds to the relative size of corpus callosum; however, this is not true in females.
Many studies suggest that, on average, female brains have more commissural tracts involved in inter-hemispheric connectivity than males.
[92] Studies using MRI scanning have shown that the auditory and language-related regions in the left hemisphere are proportionally expanded in females versus in males.
Conversely, the primary visual, and visuo-spatial association areas of the parietal lobes are proportionally larger in males.
He concluded that "men and women apparently achieve similar IQ results with different brain regions, suggesting that there is no singular underlying neuroanatomical structure to general intelligence and that different types of brain designs may manifest equivalent intellectual performance.
In short, males and females apparently achieve similar IQ results with different brain regions.
The male amygdala was believed to be proportionally larger than that in females, causing sex to be a determining factor in reactions to stress.
[106] The hippocampus, crucial for memory storage and spatial mapping of the physical environment, was likewise thought to be larger in females than in males.
[128] The longer average life span of females can lead to skewed statistical results in regard to sex differences.
[129] The gender gap in life expectancy suggests differences in the aging process between males and females.
[130] These age-related changes in the expression of double-strand break repair pathways were observed to be distinctly different in men and women.
[133] The following trends are shown: Infectious disease prevalence varies - this is largely due to cultural and exposure factors.
