Biological Differences Between the Sexes: Overview

Biological Differences

Aristotle described women as deformed men. Men's Y chromosome has been described as a decrepit X chromosome. But how different are the sexes? We will explore from larger, more obvious things to the smaller, less obvious ones.

There are some obvious differences in terms of physiology and biology. These are all generalities, meaning that it is true in most cases, but not all. Height, muscle, and adipose, or fat tissue, are different in men and women. However, there are some more and less known differences.

Chromosomes

Starting with the basics, human females possess two X chromosomes on their 23rd pair of chromosomes, while males possess an XY on their 23rd pair. Chromosomes are a structure located inside the nucleus that carries DNA. This minor variation is what differentiates males from females on a genetic level, which gives rise to all of the biological differences.

The only difference is on the 23rd pair

Physique and Life Span

Males are typically taller than females. In terms of height, the average human male is 5'10', while the average female is 5'4'. This is a result of a taller skeletal structure, resulting in heavier and larger bones.

Human males usually have more muscle above the torso, while human females usually have more muscle below the torso. Typical figures point towards an approximately 15% difference in average muscle mass above and below the torso. This means males typically have stronger upper bodies, and females have stronger legs. In addition, males have an exaggerated thyroid cartilage resulting in an Adam's apple.

Female's pelvis bones are shaped differently than males. This rule will apply to most species because the female is usually the one who produces the young (avoiding the term 'birth' here since some lay eggs). In addition, a female's bones can be altered by childbearing. It is not uncommon for calcium stripping from the bones to feed the fetus.

Female Pelvis

Male Pelvis

Human females generally have higher body fat contents than human males. On average, human males have approximately a 13% body fat percentage, while human females have a 26% body fat percentage.

Current theories reflect a relationship between menstrual cycles and body fat. If body fat drops below a certain percentage in females, the menstrual cycle can stop; the loss of menstruation is called amenorrhea. In addition, as body fat levels have increased over the last century, the age at which menstrual cycles begin has grown lower.

In addition to physique, life span is also affected by sex. It is expected that human females live, on average, seven years longer than males in a developed country. Harvard research indicates that the primary male hormone, testosterone, increases low-density cholesterol (the bad cholesterol) which causes an increase in heart and vascular problems as men age. This leads to higher chances of stroke, heart attack, and other heart-disease-related illnesses.

Evolutionary studies also suggest that the longer the female lives, the more offspring she can produce, along with the process of menopause helping to reduce the demands on the body.

The Brain

Human males typically have larger brains than females; however, larger does not mean smarter. IQ tests and aptitude tests show no physical gender bias in overall intelligence.

The difference in size has recently been linked to body mass differences, and statistics have shown that the difference in the size of a brain is comparable to the difference in a person's mass. What this is saying is a 120-pound female has a brain that is two pounds, while a 200-pound male has a five-pound brain, and both sexes have a brain that is 2.5% of their body weight.

Nearly the same

It is worth noting here that there are no or statistically insignificant differences between the sexes in math, science, and verbal abilities. A human brain develops those tendencies more from society's expectations than from anything biological.

Genitals

It almost goes without saying, but males and females possess genitals that are different. Females produce an ovule, or egg, and males fertilize the egg. This sex difference is seen in nearly every sexually reproducing species from flowers to humans. The female produces half of the genetic components and the ovule where the offspring will develop. The male produces the other half of the genetic components and is responsible for fertilizing the ovule.

The difference in genitals extends to a hormonal level, with each gender's gonads producing different hormones. Gonads here points to a male's testes or a female's ovaries, which effectively grew from the same tissue in the fetus but developed along a different trajectory.

In human and many other mammal females, the hormones fluctuate along a cycle. This cycle's purpose is to prepare the uterus for implantation of a fertilized egg. The primary hormones in females are estrogen and progesterone. In males, the primary hormone is testosterone.

Female reproductive system

Male reproductive system

Lesson Summary

The difference between males and females begins at the genetic level. The 23rd chromosome pair differs in men and women by half of a pair, with women having an XX pair and men having an XY pair. Chromosomes are a structure located inside the nucleus that carries DNA.

This difference stimulates the gonads in males to develop into testes and in females to develop into ovaries. The release of the sex hormone in males (testosterone) and in females (estrogen and progesterone) causes the bodies' sexual organs to develop into the penis and vagina.

The hormones released also affect how the skeleton develops, with males having larger and thicker bones, while females have a pelvis more suited for childbearing. In males, the muscle mass tends to be above the waist, while in females it tends to be below.

The brain size reflects the size of the body, usually being larger in males due to their robust size; however, brain size does not equate to any kind of strength or weakness, with IQ and aptitude tests reflecting no statistical difference.

Lastly, it has been found that females live longer than males, on average about seven years longer in developed countries. This has been linked to hormonal activity as well as evolutionary theory.

Learning Outcomes

Determine how well you can achieve the goals below once you've viewed this lesson:

• Perceive the chromosomal differences in males and females
• Explain the differences in males and females in terms of their reproductive systems, skeletal development, fat distribution and brain sizes
• Analyze the theories that explain why women live longer than men in developed countries