What are secondary sex characteristics? Learn the primary and secondary sex characteristics and discover their unique traits and how to identify males and females.
Updated: 07/27/2021
Types of Sex Characteristics
What Are Secondary Sex Characteristics?
Species that reproduce through sexual reproduction have multiple sexes. These sexes are defined as individuals with physiological differences that make them either male or female (though in some species there are more than two sexes). The characteristics that divide males and females are called sex characteristics. Sex characteristics are either primary or secondary depending on when they develop in an organism's life. Typically, primary sex characteristics are those that are developed and present at birth. This may include sexual organs such as the penis, testes, uterus, and ovaries. In contrast, secondary sex characteristics are those that develop as an organism enters puberty or sexual maturity. They may include body hair, particular odors, and even behaviors.
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Secondary Sex Characteristics in Humans
Have you ever really considered the differences between males and females in various species? If you have, you may have noticed the differences in physical traits between the two sexes. Without even realizing it, you were likely thinking about both primary and secondary characteristics.
While humans are born with very obvious primary sex characteristics (or body structures directly concerned with reproduction) that allows us to tell males from females, such as the penis in men and the vagina in women, secondary sex characteristics, on the other hand, are features which appear at puberty (though they later become equally as prominent). These secondary characteristics are features such as pubic hair, breast development in females, and beards in males. The list below shows some of these characteristic differences between human males and females. In men, these include:
- More pronounced body hair characteristics (beard, chest, etc.) and usually more coarse
- Heavier musculature
- Angular features (i.e. square jaw, triangular mid region)
- Narrow hips
- Muscular pectorals (chest)
- Less fat tissue overall
- Deeper voice
In women, these include:
- Less pronounced body hair characteristics (mostly in pubic region, hair all over is usually finer)
- Lighter musculature
- Rounded features (i.e. softer facial features, hourglass mid-region)
- Wider hips (for child bearing)
- More pronounced breasts with more fatty tissue
- More fat tissue overall
- Higher voice
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Primary Sex Characteristics Versus Secondary Sex Characteristics
Primary sex characteristics should be identifiable in an organism at its birth. This will include all reproductive organs that are used in sexual activity. In addition, gametes (reproductive haploid cells) are often present in organisms (especially females) at the time of their births and may be observed through medical sampling. Other primary characteristics include differences in genetic makeup, such as the presence of an X and Y chromosome in humans.
Secondary sex characteristics' definition states that they will not be identifiable at birth. By definition, these characteristics develop as an animal matures and becomes sexually active, but are not structures that are used in sexual activity. For humans, secondary sexual characteristics include things such as the development of breasts in women or angular features and thicker body hair in men. Secondary sexual characteristics have an evolutionary purpose: increase the chance of breeding. Males may have more color or sing a loud, attractive song to entice a female to mate with them. These traits wouldn't be needed in the female, who doesn't typically work to attract a male in most animal species. Males may also compete for females, so the development of large, strong antlers, tusks, or horns may be required to compete with other males. This may also be the reason some species have larger males, as the larger, stronger male is more likely to win and pass on his traits than the smaller, weaker male. In some reptile and insect species, the females have developed larger bodies than males to assist in their reproduction. Larger females can house larger or more eggs, and thus have more offspring. The more offspring they produce, the higher the chance that some will survive to pass on their genes.
Examples of Female Secondary Sex Characteristics
Females of most species may appear drabber than their male counterparts. However, there are instances where females have acquired traits that provide them additional benefits. Below is a list of common secondary sex characteristics found in females:
- Larger, more developed mammary tissues
- Wider hips for easier birthing
- Larger bodies in females who develop multiple eggs within the body
- Smaller bodies in species where males compete in combat
- Drab colors that aid in camouflage
- Higher percentage of fatty tissue to provide more energy to developing young
Examples of Male Secondary Sex Characteristics
Male secondary sexual characteristics typically serve two purposes:
- To work to attract a member of the opposite sex through display
- To work to claim a member of the opposite sex through combat
Males that attempt to attract females through display have some of the most interesting secondary sexual characteristics in the animal kingdom. Birds are a common example, and often have both bright displays as well as complex mating rituals. Many birds are well endowed with bright, elaborate plumage that works to grab a female's eye. Females may attribute certain aspects of a plumage (such as its color or shape) to desirable traits in a male that will increase the chance of her offspring's survival. While these traits are desirable by females, bright displays may come at a cost for males. These bright, elaborate plumages require more energy to produce than the sleek, simple plumages found on females. In addition, bright colors and dazzling accessories make some males an easy target for predators.
Some species also attract females through instinctual behaviors that develop as secondary sexual characteristics. Loud calls, complicated calls, and dances are performed by the males of some species to illustrate their physical fitness to females. In even fewer species, males may engage in building elaborate nests and structures. Secondary sexual characteristics that are behavioral are instinctual in behavior and not learned.
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Males that engage in male-to-male combat develop different secondary sex characteristics. The ideal way to attract a mate in these instances is to be stronger than the other males in the population and defend a female or group of females. Because of this, examples of secondary sexual characteristics in males that engage in male-to-male combat include elaborate horns and a higher concentration of body mass than their female counterparts. In these species, the males are usually considerably larger than the females as well. Male-to-male combat also comes with its disadvantages. Males may become injured when engaging in fights. Antlers and horns that must be regrown each season also require a costly amount of resources. In deer, for instance, males may be underweight at the end of the breeding season due to a decreased amount of food intake, larger nutrient requirement to produce antlers, and excess energy spent in sparring.
Other Perspectives in Secondary Sex Characteristics
Secondary sexual characteristics may have different perspectives based on the field in which they are discussed. In human medicine, secondary sexual characteristics typically refer to the onset of menstrual cycles in females and the development and growth of testes in males. Thus, medical professionals are often concerned with how these characteristics are functioning and their impact on other organ systems.
In science and ecology, secondary sexual characteristics are often observed as evolutionary traits. Ecologists observe populations and identify differences between males and females to unlock the secrets between why some traits disappear from populations and others are passed on. These scientists may also often try to find links between easily observed characteristics (such as bright feathers) and lesser-known traits (such as resistance to disease or more viable sperm production).
Society also considers sexual characteristics as an important aspect of life. Primary sexual characteristics may be present at birth, but secondary sexual characteristics may be altered or managed using hormone therapy. The appearance of secondary sexual characteristics may depend on a person's sexual identity or gender. Because gender is a perceived sexual identity, it is not based on an individual's physiological processes or morphological structures. This has also led to the creation of the term tertiary sexual characteristics. Tertiary sexual characteristics are non-biological traits that may depict a person's sexual identity. Examples of this are often found in the media. A doe in a cartoon may be easily recognizable as female by the lack of antlers. Animators may still add tertiary sexual characteristics to illustrate further that the character is highly feminine. The result may be a deer with long eyelashes, a figure resembling that of a female human, or even makeup.
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Lesson Summary
Sexual reproducing species have different sexes, which are physiologically different organisms that produce different reproductive cells known as gametes. Sexes are defined by sex characteristics, which are the physiological or morphological differences found between males, females, or other sexes. These characteristics are classified by if they occur at birth (primary sexual characteristics) or if they occur at sexual maturity (secondary sexual characteristics).
Examples of primary sex characteristics include:
- Penis
- Testes
- Uterus
- Ovaries
Examples of secondary sex characteristics include:
- Bright feathers on males
- Smaller bodies on females
- Development of larger breast tissue in females
- Appearance of antlers or horns in males
Bright and attractive secondary sex characteristics often develop in species where the males attempt to attract the attention of females through displays. Defensive secondary sex characteristics such as horns or large muscles develop in those that exhibit male-to-male combat.
In society, gender is a person's sexual identity and does not necessarily align with their sex. The media often portrays tertiary sex characteristics which are stereotypical traits assigned to males and females not physiologically or morphologically based that serve to indicate an individual's gender. This contrasts primary and secondary sex characteristics, which occur based on an individual's biology.
Secondary Sex Characteristics in Animals
Now, with animals, there can be some major differences. First, many animals have primary sex characteristics that are hard to see; the sex organs of birds, monkeys, and cats, for instance, are very difficult to perceive visually. Next, unlike humans, animals develop many of their secondary sex characteristics soon after birth, or they are present to some degree and increase as they mature. For example, in some birds, the males and females may begin with the same coloration, but as they mature, their colors begin to diverge more greatly, like cardinals.
Looking at them, could you guess which one is the male and which is the female? The chances are, if you didn't know already, you might guess the brighter red one to be the female, however, you would be incorrect! In the animal kingdom, many males of the species have much more distinct features to help them attract mates. Another example is peacocks; the males of the species have the more colorful and grand tale plumage. This is an example of a secondary sex characteristic in the species.
In the insect world, there are interesting differences, too. For example, unlike in higher animal species, wherein the males are somewhat larger, the female insects are often the larger sex. The female may also be more colorful, though in the insect world, it can go either way.
Lesson Summary
Secondary sex characteristics are those physical features that allow us to tell males from females, such as breasts on women and beards on men. This differs from primary sex characteristics, or body structures directly concerned with reproduction. In the animal kingdom, there are some great differences among the various animal groups, but there are also many similarities, and their examples are typically in color, size, and physical feature differences (e.g. birds' plumage).
Secondary Sex Characteristics Vocabulary
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- Primary sex characteristics: Characteristics directly concerned with reproduction to tell males from females
- Secondary sex characteristics: Secondary traits that appear at puberty differently for males and females
Learning Outcomes
As you complete the lesson, you should be able to:
- List some of the secondary sex characteristics in humans
- Describe the differences in secondary sex characteristics in other animals
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Video Transcript
Secondary Sex Characteristics in Humans
Have you ever really considered the differences between males and females in various species? If you have, you may have noticed the differences in physical traits between the two sexes. Without even realizing it, you were likely thinking about both primary and secondary characteristics.
While humans are born with very obvious primary sex characteristics (or body structures directly concerned with reproduction) that allows us to tell males from females, such as the penis in men and the vagina in women, secondary sex characteristics, on the other hand, are features which appear at puberty (though they later become equally as prominent). These secondary characteristics are features such as pubic hair, breast development in females, and beards in males. The list below shows some of these characteristic differences between human males and females. In men, these include:
- More pronounced body hair characteristics (beard, chest, etc.) and usually more coarse
- Heavier musculature
- Angular features (i.e. square jaw, triangular mid region)
- Narrow hips
- Muscular pectorals (chest)
- Less fat tissue overall
- Deeper voice
In women, these include:
- Less pronounced body hair characteristics (mostly in pubic region, hair all over is usually finer)
- Lighter musculature
- Rounded features (i.e. softer facial features, hourglass mid-region)
- Wider hips (for child bearing)
- More pronounced breasts with more fatty tissue
- More fat tissue overall
- Higher voice
Secondary Sex Characteristics in Animals
Now, with animals, there can be some major differences. First, many animals have primary sex characteristics that are hard to see; the sex organs of birds, monkeys, and cats, for instance, are very difficult to perceive visually. Next, unlike humans, animals develop many of their secondary sex characteristics soon after birth, or they are present to some degree and increase as they mature. For example, in some birds, the males and females may begin with the same coloration, but as they mature, their colors begin to diverge more greatly, like cardinals.
Looking at them, could you guess which one is the male and which is the female? The chances are, if you didn't know already, you might guess the brighter red one to be the female, however, you would be incorrect! In the animal kingdom, many males of the species have much more distinct features to help them attract mates. Another example is peacocks; the males of the species have the more colorful and grand tale plumage. This is an example of a secondary sex characteristic in the species.
In the insect world, there are interesting differences, too. For example, unlike in higher animal species, wherein the males are somewhat larger, the female insects are often the larger sex. The female may also be more colorful, though in the insect world, it can go either way.
Lesson Summary
Secondary sex characteristics are those physical features that allow us to tell males from females, such as breasts on women and beards on men. This differs from primary sex characteristics, or body structures directly concerned with reproduction. In the animal kingdom, there are some great differences among the various animal groups, but there are also many similarities, and their examples are typically in color, size, and physical feature differences (e.g. birds' plumage).
Secondary Sex Characteristics Vocabulary
|
- Primary sex characteristics: Characteristics directly concerned with reproduction to tell males from females
- Secondary sex characteristics: Secondary traits that appear at puberty differently for males and females
Learning Outcomes
As you complete the lesson, you should be able to:
- List some of the secondary sex characteristics in humans
- Describe the differences in secondary sex characteristics in other animals
To unlock this lesson you must be a Study.com Member.
Create your account
Frequently Asked Questions
What hormone causes secondary male characteristics?
Because secondary sex characteristics devlope during puberty, they are often the result of higher concentrations of male sex hormones. Testosterone is an example of such a hormone.
What is the purpose of secondary sex characteristics?
Secondary sex characteristics are typically involved in acquiring a mate or reproducing. Males that engage in male-to-male combat may get larger muscles, while those that create displays may grow bright feathers. Females may develop more mammary tissue to care for young.
When do you develop secondary sexual characteristics?
Secondary sex characteristics are those that are developed at puberty. This is different than primary sex characteristics, which are evident at birth.
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Secondary Sex Characteristics | Traits & Examples
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