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This means the brain-to-body mass ratio is, on average, approximately the same for both sexes. [83] [84] Comparing a male and a female of the same body size, an average difference of 100 grams in brain-mass is present, the male having the bigger and heavier brain. This difference of 100 grams applies over the whole range of human sizes.
Structurally, adult male brains are on average 11–12% heavier and 10% bigger than female brains. [21] Though statistically there are sex differences in white matter and gray matter percentage, this ratio is directly related to brain size, and some [ 22 ] argue these sex differences in gray and white matter percentage are caused by the average ...
An elephant's brain weighs just over 5 kg (11 lb), a bottlenose dolphin's 1.5 to 1.7 kg (3.3 to 3.7 lb), whereas a human brain is around 1.3 to 1.5 kg (2.9 to 3.3 lb). Brain size tends to vary according to body size. The relationship is not proportional, though: the brain-to-body mass ratio varies. The largest ratio found is in the shrew. [57]
The embryo and subsequent early fetus appear to be sexually indifferent, looking neither like a male or a female. Over the next several weeks, hormones are produced that cause undifferentiated tissue to transform into either male or female reproductive organs. This process is called sexual differentiation.
Planning began in 1986; [2] the data set of the male was completed in November 1994 and the one of the female in November 1995. The project can be viewed today at the NLM in Bethesda, Maryland. [ 3 ] There are currently efforts to repeat this project with higher resolution images but only with parts of the body instead of a cadaver.
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The ideal percent of body mass which should be fat depends on an individual's sex, age, and physical activity. For example, a female thirty year old will have a different ideal fat percentage than a male thirty year old. An athlete will have a different ideal than a non athlete, and it can depend on the sport. [24]
The bone mass in the skeleton makes up about 14% of the total body weight (ca. 10–11 kg for an average person) and reaches maximum mass between the ages of 25 and 30. [2] The human skeleton can be divided into the axial skeleton and the appendicular skeleton.