Sexual dimorphism is a phenotypic difference between males and females of the same species. The prototypical example is for differences in characteristics of reproductive organs. Other possible examples are for secondary sex characteristics, body size, physical strength and morphology, ornamentation, behavior and other bodily traits.
The average differences between males and females include all the features related to reproduction. Sexual dimorphism among humans includes differentiation among gonads, internal genitals, external genitals, breasts, muscle mass, height, the endocrine (hormonal) systems and their physiological and behavioral effects. According to Clark Spencer Larsen, modern day homo sapiens show a relatively narrow range of sexual dimorphism, with average body mass difference between the sexes being roughly equal to 15% (compared to most primates and anthropoids, ranging 50-55%). Ever since Charles Darwin’s The Descent of Man and Selection in Relation to Sex in 1871 was published, there’s been controversy regarding the social, cultural, and political significance of human sexual dimorphism. “Key points of discussion are how to interpret size dimorphism in humans and what inferences can be drawn about the evolution of human mating systems and social organization.”
The average basal metabolic rate is about 6 percent higher in adolescent males than females and increases to about 10 percent higher after puberty. Females tend to convert more food into fat, while males convert more into muscle and expendable circulating energy reserves. Aggregated data of absolute strength indicates that females have, on average, 40-60% the upper body strength of males, and 70-75% the lower body strength. The difference in strength relative to body mass is less pronounced in trained individuals. In Olympic weightlifting, male records vary from 5.5× body mass in the lowest weight category to 4.2× in the highest weight category, while female records vary from 4.4× to 3.8×, a weight adjusted difference of only 10-20%, and an absolute difference of about 30% (i.e. 472 kg vs 333 kg for unlimited weight classes)(see Olympic weightlifting records). A study, carried about by analyzing annual world rankings from 1980–1996, found that males’ running times were, on average, 11% faster than females’.
Females are taller, on average, than males in early adolescence, but males, on average, surpass them in height in later adolescence and adulthood. In the United States, adult males are, on average, 4% taller and 8% heavier than adult females.
Males typically have larger tracheae and branching bronchi, with about 30 percent greater lung volume per body mass. On average, males have larger hearts, 10 percent higher red blood cell count, higher hemoglobin, hence greater oxygen-carrying capacity. They also have higher circulating clotting factors (vitamin K, prothrombin and platelets). These differences lead to faster healing of wounds and higher peripheral pain tolerance.
Females typically have more white blood cells (stored and circulating), more granulocytes and B and T lymphocytes. Additionally, they produce more antibodies at a faster rate than males. Hence they develop fewer infectious diseases and succumb for shorter periods. Ethologists argue that females, interacting with other females and multiple offspring in social groups, have experienced such traits as a selective advantage.
Considerable discussion in academic literature concerns potential evolutionary advantages associated with sexual competition (both intrasexual and intersexual) and short- and long-term sexual strategies.
According to Daly and Wilson, “The sexes differ more in human beings than in monogamous mammals, but much less than in extremely polygamous mammals.” One proposed explanation is that human sexuality has developed more in common with its close relative the bonobo, who have similar sexual dimorphism and which are polygynandrous and use recreational sex to reinforce social bonds and reduce aggression.
In the human brain, a difference between sexes was observed in the transcription of the PCDH11X/Y gene pair unique to Homo sapiens. The relationship between sex differences in the brain and human behavior is a subject of controversy in psychology and society at large. Females on average have a higher percentage of gray matter in comparison to males.However, males have larger brains on average than females, and when adjusted for total brain volume the gray matter differences between sexes is small or nonexistent. Thus, the percentage of gray matter appears to be more related to brain size than it is to sex. Differences in brain physiology between sexes do not necessarily relate to differences in intellect. Haier et al. found in a 2004 study 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”.
The bed nucleus of the stria terminalis shows strong sexual dimorphism and is twice as large in males as in females.
Studies have shown that ovulating heterosexual women prefer faces with masculine traits associated with increased exposure to testosterone during key developmental stages, such as a broad forehead, relatively longer lower face, prominent chin and brow, chiseled jaw and defined cheekbones. The degree of differences between male and female anatomical traits is called sexual dimorphism. Female respondents in the follicular phase of their menstrual cycle (n = 55) were significantly more likely to choose a masculine face than those in menses and luteal phases (n = 84), (or in those taking hormonal contraception). It is suggested that the masculinity of facial features is a reliable indication of good health, or, alternatively, that masculine-looking males are more likely to achieve high status. However, the correlation between attractive facial features and health has been questioned. Sociocultural factors, such as self-perceived attractiveness, status in a relationship and degree of gender-conformity, have been reported to play a role in female preferences for male faces. Studies have found that women who perceive themselves as physically attractive are more likely to choose men with masculine facial dimorphism, than are women who perceive themselves as physically unattractive. In men, facial masculinity significantly correlates with facial symmetry—it has been suggested that both are signals of developmental stability and genetic health. One study called into question the importance of facial masculinity in physical attractiveness in men arguing that when perceived health, which is factored into facial masculinity, is discounted it makes little difference in physical attractiveness. In a cross-country study involving 4,794 women in their early twenties, a difference was found in women’s average “masculinity preference” between countries.
A study found that the same genetic factors cause facial masculinity in both males and females such that a male with a more masculine face would likely have a sister with a more masculine face due to the siblings having shared genes. The study also found that, although female faces that were more feminine were judged to be more attractive, there was no association between male facial masculinity and male facial attractiveness for female judges. With these findings, the study reasoned that if a woman were to reproduce with a man with a more masculine face, then her daughters would also inherit a more masculine face, making the daughters less attractive. The study concluded that there must be other factors that advantage the genetics for masculine male faces to offset their reproductive disadvantage in terms of “health”, “fertility” and “facial attractiveness” when the same genetics are present in females. The study reasoned that the “selective advantage” for masculine male faces must “have (or had)” been due to some factor that is not directly tied to female perceptions of male facial attractiveness. The study said that the selection for masculine male faces could be due to the indirect result of female preferences for “correlated traits” such as bodily muscularity or assertive tendencies. The study also said women could possibly judge more masculine faces as being more attractive in “certain contexts or populations” or during ovulation, even though more masculine male faces are not judged by women as more attractive overall. Alternatively, the study said that the selection for “robust” male faces could be due to a “survival or reproductive advantage” by which greater robustness is better suited for “physical damage” in male-male competition or facial robustness may indicate “dominance to male competitors”.
In a study of 447 gay men in China, researchers said that tops preferred feminized male faces, bottoms preferred masculinized male faces and versatiles had no preference for either feminized or masculinized male faces
Digit Ratio Theory
The digit ratio is the ratio of the lengths of different digits or fingers typically measured from the midpoint of bottom crease where the finger joins the hand to the tip of the finger.
For Female, the ring finger and index finger are either same in length or longer ring finger. While for males the story is that we see longer ring finger then index finger.
while becoming a male from female we need to:
- lose our female sexual organ to grow male sexual organ
- grow longer ring finger
- large torso and feet