The Martin Pollins Blog

History, economics, business, politics…and Sussex

Martin Pollins

, ,
No comments on Evolution, Nipples and the Legacy of Vestigial Traits

Evolution, Nipples and the Legacy of Vestigial Traits

Introduction[1]

First, it’s useful to note that the nipple is not considered an organ in the strict biological sense. Instead, it is classified as a specialised structure that is part of the skin (the integumentary[2] system) and the mammary gland system. To understand its classification, we can look at the context of related structures:

  • The Skin as an Organ: The skin is not only an organ, it is the largest organ in the body of mammals, including humans. It performs multiple essential functions, including protection, thermoregulation, sensory reception, and acting as a barrier against external elements. This well-established fact underscores its importance as a complex, multifunctional organ.
  • The Nipple’s Function as an Outlet: The nipple serves as the external projection through which the lactiferous ducts deliver milk. It acts as the outlet for the mammary gland system, which is critical during breastfeeding. As part of the skin, the nipple’s role aligns with the integumentary system’s functions while connecting directly to the mammary glands.
  • The Mammary Glands as an Organ: The mammary glands, which encompass the alveoli, ducts, and supporting tissues, function as a cohesive unit to produce and deliver milk. This makes the mammary glands a functional organ within the body, working in response to hormonal and sensory signals.
  • The Nipples Are NOT an Organ: On its own, the nipple does not qualify as an organ because it lacks independent functionality. It is a specialised component of the skin and mammary gland system, designed to facilitate milk delivery and respond to stimuli. While it is highly functional within its role, it does not operate independently of these larger systems.

The title and subject of this paper, I’ll readily admit, is rather unusual. Humans almost always have two nipples, one on each side of the chest. This is the typical anatomical pattern in line with our bilateral symmetry and mammalian characteristics. However, there are exceptions due to genetic variations or developmental anomalies.


Image of a mother pig nursing her piglets while looking at the camera in a natural farm setting.
Drawn by DALL-E, a subset of ChatGPT, 12/12/2024
Common Exceptions to the Two Nipples Structure

  • Supernumerary Nipples (Polythelia): Some people are born with extra nipples along the “milk lines,” which run from the armpits to the groin on both sides of the body. These extra nipples can look like small moles or fully developed nipples and are usually harmless. Around 1-5% of the population has this condition.
  • Congenital Absence of Nipples (Athelia): In rare cases, mammals may be born without one or both nipples. This condition is typically linked to genetic or developmental disorders affecting the chest, such as Poland syndrome, but the underlying mammary gland structure remains intact.
  • Amastia: Even more rarely, mammals are born without any mammary gland tissue, including the nipples. Unlike athelia, this condition involves the complete absence of the mammary gland structure, not just the nipple.
  • Surgical Removal or Trauma: Nipples can be surgically removed or lost due to trauma, injury, or medical conditions such as mastectomy for breast cancer treatment.

Number of Nipples

Nipples are a characteristic feature of mammals because they are part of the mammalian class’s unique ability to feed their young with milk. All mammals that give live birth (placental mammals and marsupials) have nipples, though the number, size, and placement vary widely depending on the species:

  • Humans, like most mammals, typically have one pair of nipples corresponding to the single offspring or limited litter size humans are evolutionarily adapted to nurse.
  • In animals with larger litters (e.g., cats, dogs, or pigs), the number of nipples is higher to match the need for feeding multiple young.


The breast: cross-section scheme of the mammary gland: 1. Chest wall 2. Pectoralis muscles 3. Lobules 4. Nipple 5. Areola 6. Milk duct 7.Fatty tissue 8.Skin
Citation: Nipple. (2024, December 9). In Wikipedia. https://en.wikipedia.org/wiki/Nipple
Attribution: Original by Patrick J. Lynch. Reworked by Morgoth666 to add numbered legend arrows, CC BY 3.0 <https://creativecommons.org/licenses/by/3.0&gt;, via Wikimedia Commons


Species Having Nipples

Only mammals have nipples. Nipples are a defining characteristic of mammals, as they are part of the mammary gland system used to produce and deliver milk to offspring. No other class of animals, such as birds, reptiles, amphibians, fish, or invertebrates, has nipples.

Why Nipples Are Exclusive to Mammals:

  • Mammalian Lactation: Nipples are associated with the mammalian ability to nurse young using milk produced by mammary glands. This is a unique evolutionary adaptation found only in mammals.

Non-mammalian animals provide nourishment to their offspring in different ways, such as:

  • Birds: Many birds regurgitate partially digested food to feed their chicks.
  • Reptiles and Amphibians: These animals often leave their offspring to survive independently, although some provide care without directly feeding their young.
  • Fish: Certain fish, such as discus fish, secrete a nutrient-rich mucus from their skin for their young to consume. While this provides nourishment, it is not comparable to lactation or the use of nipples in mammals.

Exceptions in Mammals
Nipples are an exclusive and defining feature of mammals, reinforcing their unique role in nourishing their young through lactation. Even among mammals, there are slight variations:

  • Monotremes[3] (like platypuses and echidnas): These mammals do not have distinct nipples but secrete milk through specialised patches of skin, which their young lap up.

Examples of Species with Nipples:

  • Primates: Humans, monkeys, and apes all have nipples, typically two, positioned on the chest.
  • Carnivores: Dogs, cats, lions, and tigers have multiple nipples, usually along the abdomen.
  • Rodents: Rats, mice, and squirrels have nipples along the belly, with numbers varying depending on the species.
  • Ungulates: Horses, cows, goats, and deer have fewer nipples (e.g., cows have four, goats two, and are typically positioned on an udder).[4]
  • Marsupials: Kangaroos, koalas, and opossums have nipples inside a pouch to nourish their underdeveloped young.
  • Cetaceans: Whales, dolphins, and porpoises have hidden nipples near the genital area, from which milk is ejected into the water for their calves.
  • Pinnipeds: Seals and sea lions have nipples, though often less visible due to their streamlined bodies.
  • Chiroptera (bats): Bats typically have two nipples for feeding their pups.
  • Elephants: Elephants have two nipples located between their forelegs.
  • Monotremes: Although monotremes like platypuses and echidnas don’t have prominent nipples, they excrete milk through mammary gland openings or patches.

As previously mentioned, nipples are absent in species that do not produce milk, such as reptiles, birds, amphibians, and fish.


Farm Animals

All farm animals that are mammals have nipples. This is because nipples are a characteristic feature of mammals, as they are part of the mammalian adaptation for feeding offspring through milk produced by mammary glands. Cows, goats, sheep, pigs, horses, and donkeys all have nipples, although their number, size, and arrangement vary depending on the species and their typical litter size.


Three Blonde d’Aqutaine calves from embryo transfer suckling at one cow.png by Blonde d’Aquitaine is licensed under CC BY-SA 3.0.

Mammals and Nipples in Farm Animals

  • Cows: Cows have four nipples (teats) on their udders, which are used for feeding their calves and for milking.
  • Goats and Sheep: These animals usually have two teats, corresponding to their relatively small litter sizes.
  • Pigs: Sows often have 12 to 14 nipples (or more) to nurse their large litter.
  • Horses and Donkeys: Mares and jennies (female horses and donkeys) have two teats located near their groin, adapted for nursing a single foal.

Non-Mammalian Farm Animals
Farm animals that are not mammals, such as chickens, ducks, and other poultry, do not have nipples because they do not produce milk or nurse their young. Instead, these animals provide nourishment in other ways:

  • Birds lay eggs, and their offspring are fed by pecking at food provided by parents or foraging on their own.
  • In some cases, such as pigeons, parents produce a milk-like substance (crop milk[5]) to feed their chicks, but this does not involve nipples.

Species Where Both Sexes Have Nipples

Both sexes having nipples is not limited to humans and is common across most mammals. Here’s why this happens and how it applies to other species:

Developmental Basis
In mammals, nipples form during the early stages of embryonic development, often before the genetic switch that determines biological sex (via chromosomes like XY or XX). Because of this, both males and females develop nipples, but their function differs:

  • Females: Nipples are essential for lactation and nursing offspring.
  • Males: Nipples are typically vestigial, meaning they exist without a functional purpose in most species.

Species Where Both Sexes Have Nipples

  • Primates: Male and female primates (monkeys, apes, etc.) have nipples, similar to humans.
  • Carnivores: In dogs, cats, and other carnivores, both sexes possess multiple nipples along the abdomen, though only females lactate.
  • Rodents: Both male and female rodents, like rats and mice, have nipples, but males lack mammary gland functionality.
  • Marsupials: Male marsupials (like kangaroos) may have rudimentary nipples, but these are typically less prominent.
  • Cetaceans: Male whales and dolphins have concealed nipples near their genital area, although they serve no function in nursing.

Exceptions
There are some species of mammals where males do not have nipples:

  • Horses: Male horses (stallions) typically do not have visible nipples.
  • Monotremes: In monotremes, neither males nor females have distinct nipples; milk is secreted through specialised mammary gland patches.

Evolutionary Perspective
The presence of nipples in both sexes is primarily due to the efficiency of early embryonic development. Removing or suppressing nipple development in males offers no evolutionary advantage, so the feature is retained as a neutral trait.

Both sexes having nipples is common across mammals, not just in humans. However, the prominence and visibility of nipples in males vary by species.


Vestigial

The word Vestigial refers to a structure or feature in an organism that has lost most or all of its original function through the course of evolution. These features may still exist because they were functional in the organism’s ancestors but are no longer necessary in the current species.

Characteristics of Vestigial Structures

  • They are often reduced in size or prominence compared to their original form in ancestors.
  • They may have no clear purpose in the organism or may perform a different, less significant function.

Examples in Humans

  • Appendix: Originally thought to have aided in digesting cellulose-rich diets in early human ancestors, the appendix now serves a minor role in immune function.
  • Wisdom Teeth: These extra molars were useful for grinding tough plant materials in early human diets but are often problematic in modern humans.
  • Tailbone (Coccyx): A remnant of ancestral tails, it now provides support for pelvic muscles.
  • Goosebumps: These occur when tiny muscles contract to raise body hair, which helped ancestral species appear larger or stay warm, but they have little use in modern humans.

Examples in Animals

  • Wings in Flightless Birds: Ostriches and penguins have wings that are not used for flight. Instead, ostriches use their wings for balance and display, while penguins use theirs as flippers for swimming. These wings are considered vestigial in terms of flight capability. (Note: Birds belong to the class Aves and are not mammals.)
  • Eyes in Cave-Dwelling Animals: Many cave-dwelling species, such as cavefish and some moles, have vestigial eyes. These eyes are often non-functional or greatly reduced, as their dark environments eliminate the need for vision. (Note: Cavefish are fish, not mammals, while moles are mammals within the class Mammalia.)
  • Leg Bones in Whales and Snakes: Some whales and snakes retain small, hidden leg bones that are remnants of their land-dwelling ancestors. In whales, these vestigial bones are buried within their bodies, while in snakes, they may appear as tiny spurs near the tail. (Note: Whales are mammals, but snakes are reptiles within the class Reptilia.)

In short, a vestigial structure is a fascinating reminder of an organism’s evolutionary history, showcasing how traits adapt or become redundant over time.


Broader Vestigial Structures

Additional Vestigial Structures in Humans:

  • Palmar Grasp Reflex: The ability of newborns to grasp objects tightly with their hands is thought to be a remnant of primate ancestors who needed to cling to their mothers.
  • Auricular Muscles: The small muscles around human ears allow for minimal movement but are vestigial remnants of ancestors who could swivel their ears to detect sounds.
  • Plica Semilunaris (Third Eyelid): This small fold of tissue in the inner corner of the eye is a remnant of a nictitating membrane[6], which some animals use to protect and moisten their eyes.
  • Body Hair: While humans retain hair for warmth and sensory functions, the fine hair covering most of the body has little practical purpose compared to the dense fur of ancestors.

Vestigial Features in Other Mammals:

  • Hind Limb Spurs in Snakes: Some snakes, such as boas and pythons, retain small external spurs that are remnants of hind limbs.
  • Dewclaws in Dogs: These extra digits, often found on the inside of the front or hind legs, are largely unused in modern dogs but were likely functional in their ancestors.


Dog‘s dewclaw that is a little overgrown on this 13-year-old dog, although its end remains worn smooth from contact with the ground while running. Taken by Elf
Creative Commons Attribution-Share Alike 3.0

Vestigial Structures in Non-Mammals:

  • Pelvic Spines in Stickleback Fish: Some populations of these fish have reduced pelvic spines, which are vestigial in environments where predators do not grab them by their lower bodies.
  • Flight Muscles in Flightless Birds: Ostriches and emus retain rudimentary flight muscles that are no longer used for flying.
  • Vestigial Tails in Frogs: Tadpoles develop tails for swimming, but these are absorbed as frogs mature, leaving no trace in adult frogs.

Nipples and Evolutionary Perspectives

Male Nipples in Other Species:

  • Lions and Tigers: Like many mammals, male big cats have nipples despite their lack of function.
  • Bats: Male bats sometimes have nipples, though their exact function is species-dependent.

Evolutionary Theories on Nipples in Males:

  • Developmental Economy: Nipples form before the embryo differentiates into male or female, making their presence in males an evolutionary “default.”
  • Potential Use in Some Species: While rare, some species (like male Dayak fruit bats) have been observed to produce milk under certain conditions.

Non-Mammalian Lactation-Like Behaviours
  • Pigeons and Crop Milk: Male and female pigeons both produce a nutrient-rich substance in their crop to feed their chicks. While not comparable to lactation, this behaviour serves a similar nurturing role.
  • Cockroaches (Diploptera punctata): This species, a viviparous insect, produces a milk-like secretion in its brood sac to nourish its live-born young. (Note: while this is a remarkable feeding strategy, it is not the same as mammalian lactation and does not involve nipples.)

Cultural and Symbolic Aspects of Nipples and Vestigial Structures

Cultural Significance of Nipples:

    • Depictions in art and literature often symbolise femininity, fertility, and nurturing.
    • Historical beliefs and superstitions about extra nipples, often associated with witchcraft in medieval Europe.

Vestigial Structures in Folklore:

  • Tales or myths explaining body features, such as why humans have a tailbone or why animals lose certain traits, often serve as allegories for change or adaptation.


Coccyx. Shown in red.
Attribution: BodyParts3D is made by DBCLS, CC BY-SA 2.1 JP <https://creativecommons.org/licenses/by-sa/2.1/jp/deed.en&gt;, via Wikimedia Commons


Technological and Medical Relevance

Vestigial Structures in Medical Studies:

  • Appendix Function in Immunity: While vestigial in digestion, its role in harbouring beneficial gut bacteria is an area of ongoing study.
  • Wisdom Teeth in Dentistry: Removal of vestigial wisdom teeth is one of the most common surgical procedures in modern medicine.
  • Coccyx Injuries: Despite its reduced function, the coccyx can still cause discomfort or pain if injured.

Nipples in Reconstructive Surgery:

  • Advances in mastectomy and reconstructive surgery often focus on preserving or reconstructing the nipple for aesthetic and psychological reasons.
  • Tattooing techniques to recreate realistic-looking nipples after surgery.

Vestigial Behavioural Traits
  • Startle Reflex in Humans (Moro Reflex): This reflex, observed in infants, causes them to throw out their arms when startled, likely a survival trait from ancestors who needed to cling to caregivers.
  • Dogs’ Circling Before Lying Down: Dogs often circle before lying down, a behaviour thought to be vestigial from ancestors who needed to flatten grass or check for predators.

Cross-Species Comparisons
Vestigial structures occur across diverse classes of animals, offering insights into the ways evolution shapes different lineages. In mammals, structures like the appendix or wisdom teeth are remnants of adaptations suited for herbivorous diets or large jaw structures. Birds, by contrast, exhibit vestigial wings in flightless species like ostriches and emus, which now serve purposes such as balance or display. Reptiles, such as pythons and boas, retain vestigial hind limb spurs, reminders of their terrestrial ancestors. Even fish, such as sticklebacks, display reduced pelvic spines in certain populations, adapting to predator-free environments. These examples illustrate how evolutionary pressures and environmental factors shape vestigiality uniquely in each group.


Functional Vestigial Structures

Not all vestigial structures are entirely without purpose. Some retain minor or secondary roles. For instance, the appendix, which was once thought to be completely redundant, is now recognised as a reservoir for beneficial gut bacteria, contributing to immune system health. Similarly, goosebumps, a reflex inherited from furry ancestors, may have minimal thermoregulatory benefits in humans today. This duality—partial redundancy yet occasional functionality—underscores how evolutionary remnants can persist when they pose no significant disadvantage and may still provide some limited benefits.


Behavioral Vestigiality

Vestigiality is not restricted to physical structures; certain behaviours also fall into this category. For instance, human infants exhibit the Moro reflex, flinging their arms wide when startled. This reflex is believed to be a vestige of primate ancestors who needed to cling to their mothers for survival. Similarly, dogs often circle before lying down, a behaviour thought to originate from their wild ancestors’ need to flatten grass or check for predators. These behaviours, while no longer critical for survival, persist as evolutionary echoes of once-essential instincts.


Controversies and Misconceptions

The concept of vestigiality often invites debate and misunderstanding. A common misconception is that vestigial structures are entirely useless, whereas many retain limited or altered functions, such as the appendix’s role in immunity. Similarly, not all reduced or seemingly purposeless traits are vestigial; some may serve hidden or context-specific purposes. For instance, reduced structures in certain animals might be adaptations rather than remnants. These nuances emphasise the need for precise scientific analysis when identifying and classifying vestigial features.


Vestigiality in Pathology

Vestigial structures can sometimes lead to medical challenges. Wisdom teeth, vestigial molars that once aided in grinding tough plant material, often cause overcrowding or infection in modern humans with smaller jaws. Similarly, appendicitis, an inflammation of the vestigial appendix, remains a common medical emergency. Even the coccyx, though it serves as a point of muscle attachment, can cause significant pain or discomfort if injured. These examples highlight how vestigial structures, while fascinating markers of evolution, can have practical implications in healthcare.


Nipples in Evolutionary Biology

Nipples serve as a unifying trait among mammals, reflecting the shared ancestry and evolutionary innovation within the class. Their presence across species, even in males where they are typically non-functional, underscores the efficiency of embryonic development and the shared genetic blueprint of mammals. Exceptions like monotremes, which lack distinct nipples but secrete milk through skin patches, demonstrate the diversity of mammalian adaptations. This uniformity and variation alike offer valuable insights into developmental biology and the evolutionary pressures that shape life.


Conclusion

The exploration of nipples and vestigial structures reveals a fascinating intersection of anatomy, evolution, and adaptation. Nipples, a defining characteristic of mammals, exemplify the functional specialisation of biological structures, while vestigial traits highlight the evolutionary journey of various species. Together, they serve as reminders of the complexity and interconnectedness of life on Earth, illustrating how form and function adapt—or fail to adapt—to changing environments and lifestyles.

The study of vestigial structures, such as the human appendix, whale leg bones, or the wings of flightless birds, underscores the iterative nature of evolution. These remnants, while seemingly purposeless, provide a window into the past, helping us trace the lineage and adaptations of species over millions of years. They also challenge the misconception that evolution is a linear march toward perfection; instead, it is a dynamic process shaped by survival, environmental pressures, and genetic variation.

Nipples, though seemingly simple, embody the evolutionary ingenuity of mammals. Their presence across species, even in males where they are often vestigial, reflects the efficiency of embryonic development and the shared ancestry of mammals. Exceptions, such as monotremes that secrete milk through skin patches, further highlight the diversity of evolutionary strategies within this class. These structures, functional or vestigial, remind us of the evolutionary constraints and innovations that shape life.

Understanding these features is not just an academic exercise but also has profound implications for medicine, conservation, and even culture. Vestigial structures like wisdom teeth and the appendix influence healthcare decisions, while the study of evolutionary traits can guide efforts to conserve endangered species. Furthermore, the symbolic and cultural significance of features like nipples demonstrates how biology influences art, identity, and social constructs.

Ultimately, the interplay between functional and vestigial traits demonstrates nature’s capacity for adaptation and resilience. Even as species evolve and environments change, the remnants of the past persist, offering insights into the shared evolutionary history of life. Nipples and vestigial structures stand as testaments to the intricate processes that govern biology, blending functionality with the echoes of evolutionary history. This review of anatomical traits bridges science, culture, and evolution, encouraging us to view even the simplest features with curiosity and reverence. By studying these characteristics, we not only gain a deeper understanding of our own biology but also appreciate the diversity and adaptability of life across species.


Appendix: Did You Know?

The ancient Greeks and Romans had specific terms to refer to nipples, reflecting their understanding of anatomy and their cultural and medical traditions. Here’s what they called them:

In Ancient Greek

  • Μαστός (Mastos): This term was used broadly to refer to the breast or the nipple. It appears in medical texts and literature, often describing the female breast, particularly in contexts related to nursing or fertility. Example Usage: The term appears in the works of Hippocrates and other ancient Greek medical texts when discussing breast health or lactation.
  • Θηλή (Thēlē): Specifically used for the nipple itself. The word relates to “a small teat” or “protuberance” and is derived from a root meaning “to suckle” or “to nurse.” Example Usage: Thēlē is frequently used in descriptions of nursing or breast anatomy in classical texts.

In Latin

  • Mamma: Like the Greek mastos, mamma referred to the breast as a whole. It was commonly used in Latin texts about anatomy, maternal care, and even poetry. Example Usage: Cicero and Pliny the Elder used mamma to discuss the female breast.
  • Papilla: This term specifically described the nipple and is derived from the root pap- (to feed or nourish). Papilla has endured in modern anatomical terminology as a scientific term for the nipple. Example Usage: In Roman medical texts, papilla referred to the nipple, particularly in discussions of breastfeeding or breast-related conditions.

Cultural Context

  • In both Greek and Roman societies, the nipple and breast were closely associated with motherhood, fertility, and nourishment. Art and literature often depicted nursing mothers or goddesses symbolising these qualities (for example, Artemis and the she-wolf nursing Romulus and Remus).
  • Medical texts, such as those by Hippocrates (Greek) and Galen (Greek physician working in Rome), discussed the anatomy of the breast and nipple in detail, often using thēlē or papilla to refer to the nipple.

These terms continue to influence modern anatomical and medical vocabulary.

The word “Nipple” itself has a fascinating etymological history rooted in Middle English and Old English.

Here’s an exploration of its origins:

  • Middle English Roots: The term “nipple” first appeared in Middle English as nypel, derived from an earlier form neb, which meant “small projection” or “protuberance.” This usage reflects the physical shape of the nipple.
  • Old English Influence: The Old English word neb or hnæb referred to a “beak” or “nose,” highlighting the idea of a protruding structure. Over time, this meaning extended to include other small, pointed projections, such as the nipple.
  • Germanic Roots: Neb has cognates in other Germanic languages, such as Middle Low German nebbe (beak) and Dutch nebbe (nose or beak). These terms emphasise the association with protruding forms.
  • Evolution in Form and Meaning: By the late Middle Ages, the word evolved to refer specifically to the anatomical structure of mammals. The diminutive suffix -el was added to form “nipple,” signifying a smaller or more specific part of the body.
  • Latin and Romance Influence: While “nipple” itself is not derived directly from Latin, there is some overlap in medical and anatomical terminology. For example, the Latin term papilla (small pimple or teat) is used in scientific contexts, and its influence is seen in related terms like “papillary.”
  • Modern Usage: The term “nipple” became standard in English during the 17th century, cementing its association with mammalian anatomy and breastfeeding.

Here are several things about Nipples, you may not have known:

  1. Nipples Develop First in the Womb: Nipples form before the differentiation of sexual organs, which is why both men and women have them.
  2. Areolae Come in All Shapes and Sizes: The areolae, the coloured skin around the nipples, vary greatly in size and shade, from barely noticeable to as large as a plate.
  3. Named Glands on Areolae: The small bumps on the areolae are called Montgomery glands, named after William Montgomery[7], who first described them scientifically.
  4. Supernumerary Nipples Are Common: Extra nipples, called supernumerary nipples, can appear along the “milk lines” that extend from the armpit to the groin. These are often mistaken for moles.
  5. Some People Have More Than Six Nipples: While most have one or two extras, cases of individuals with seven or more nipples have been documented.
  6. The Distance Between Nipples Matches Your Earlobes: The space between your nipples roughly equals the distance between your earlobes.
  7. Nipples Can Cause Orgasms: For some individuals, nipple stimulation alone can trigger orgasm due to the high density of nerve endings.
  8. Nipples Can Be Inverted: Up to 20% of women experience inverted nipples, caused by shorter milk ducts pulling the nipples inward.
  9. Human Nipples Are Unique Among Mammals: Unlike other mammals, human nipples remain prominent throughout life, regardless of pregnancy or lactation.
  10. World’s Strongest Nipples: A man known as The Great Nippulini lifted 32 kilograms per nipple, earning him a Guinness World Record.
  11. Nipple Changes Signal Health Issues: Sudden changes, such as dimpling, hardening, or scabbing, can indicate underlying health problems and should be checked by a doctor.
  12. Nipples Are Highly Sensitive: Packed with sensory nerve endings, nipples are among the most sensitive areas of the human body.
  13. Not All Mammals Have Prominent Nipples: Monotremes, such as platypuses, lack distinct nipples, secreting milk through skin patches instead.
  14. Men Can Lactate: While extremely rare, men can produce milk under certain hormonal conditions, such as high prolactin levels.
  15. Goosebumps Extend to Nipples: The small muscles responsible for goosebumps also contract around the areola, making nipples erect in response to cold or touch.
  16. Male Nipples Are Mostly Vestigial: Although present in nearly all males, nipples in men generally lack function in terms of lactation.
  17. Nipple Hair is Normal: Small hairs around the areola are common and serve no specific purpose other than being a byproduct of follicular activity.
  18. Nipples Can Change Colour: Hormonal changes, such as pregnancy, can darken the nipples and areolae, often permanently.
  19. Nipple Piercings Are Ancient: Historical records suggest nipple piercings date back to Roman soldiers and indigenous cultures, often symbolising strength or fertility.
  20. Nipples in Art and Culture: Throughout history, nipples have been symbols of nourishment, femininity, and sensuality in art and literature, from ancient sculptures to modern media.
  21. Nipple Pigmentation Changes Over Time: Nipples and areolae often darken during puberty and pregnancy, but they can also lighten with age or hormonal shifts.
  22. Nipples Are Unique Like Fingerprints: No two people have identical nipples, as size, shape, colour, and texture vary greatly among individuals.
  23. Men Have Breast Cancer Too: While less common than in women, men can develop breast cancer, and symptoms often include changes in the nipple, such as discharge or inversion.
  24. Nipple Shield Use in History: Breastfeeding mothers in Victorian times often used decorative nipple shields made from silver or ivory to prevent chafing.
  25. Some Animals Have Functional Male Nipples: In certain species, such as Dayak fruit bats, males have been observed producing milk under specific conditions.
  26. Nipples Can Be Hypersensitive During Certain Phases: Hormonal fluctuations, such as during menstruation or pregnancy, can make nipples more sensitive than usual.
  27. Nipples Can Have Freckles or Moles: Like any part of the skin, nipples can develop freckles or moles, which are usually harmless but should be monitored for changes.
  28. The Nipple-Areola Complex Aids Infant Latching: The darker areola and erect nipple provide a visual and tactile cue for infants to latch on properly during breastfeeding.
  29. Nipples Can Have Allergic Reactions: Certain fabrics, detergents, or creams can irritate the sensitive skin of the nipple, causing discomfort or itching.
  30. Nipples in Mythology and Superstition: In some cultures, extra nipples were historically associated with witchcraft or supernatural powers, particularly in medieval Europe.
  31. The mammal with the most nipples—36 (18 pairs)—is represented by two species. The first is the tailless tenrec (Tenrec ecaudatus), a spiny insectivorous mammal from Madagascar, about the size of a Chihuahua, capable of birthing up to 31 offspring per litter—a record among mammals. The second is the Natal multimammate rat (Mastomys natalensis), a rodent native to Africa, particularly Nigeria, and a known natural reservoir for the Lassa fever virus.[8]
  32. Male mice are born without nipples. Male horses and platypuses also are born without nipples.[9]

Sources and Further Reading

Books

NOTICE: This paper is compiled from the sources stated but has not been externally reviewed. Some content, including image generation and data synthesis, was assisted by artificial intelligence, but all findings were reviewed and verified by us (the author and publisher). Neither we (the publisher and author) nor any third parties provide any warranty or guarantee regarding the accuracy, timeliness, performance, completeness or suitability of the information and materials covered in this paper for any particular purpose. Such information and materials may contain inaccuracies or errors, and we expressly exclude liability for any such inaccuracies or errors to the fullest extent permitted by law. Your use of any information or materials on this website is entirely at your own risk, for which we shall not be liable. It shall be your own responsibility to ensure that any products, services or information available through this paper meet your specific requirements. You should neither take action nor exercise inaction without taking appropriate professional advice. The hyperlinks were current at the date of publication.


End Notes and Explanations
  1. Source: Compiled from my research using information available at the sources stated throughout the text, together with information provided by machine-generated artificial intelligence at: bing.com [chat] and https://chat.openai.com. Text used includes that on Wikipedia websites is available under the Creative Commons Attribution-ShareAlike License 4.0; additional terms may apply. By using those websites, I have agreed to the Terms of Use and Privacy Policy. Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc., a non-profit organisation. ↑
  2. Explanation: The integumentary system is the set of organs forming the outermost layer of an animal’s body. It comprises the skin and its appendages, which act as a physical barrier between the external environment and the internal environment it serves to protect and maintain the body of the animal. Mainly it is the body’s outer skin. The integumentary system includes skin, hair, scales, feathers, hooves, claws, and nails. It has a variety of additional functions: it may serve to maintain water balance, protect the deeper tissues, excrete wastes, and regulate body temperature, and is the attachment site for sensory receptors which detect pain, sensation, pressure, and temperature. Source: https://en.wikipedia.org/wiki/Integumentary_system ↑
  3. Explanation: Monotremes are a group of egg-laying mammals that belong to the order Monotremata. Unlike placental mammals and marsupials, monotremes reproduce by laying eggs rather than giving live birth, making them a unique branch of mammalian evolution. They exhibit a mix of mammalian and reptilian traits, reflecting their ancient origins. Monotremes lay eggs with leathery shells, similar to reptiles, and the young hatch in an underdeveloped state. Female monotremes secrete milk from specialised mammary gland patches rather than through nipples, and the young lap up the milk from the skin or fur. They also have a single opening, called a cloaca, for excretion and reproduction, a feature shared with birds and reptiles but not other mammals.Examples of monotremes include the platypus and echidnas. The platypus, native to Australia, is semi-aquatic and uses its bill to forage underwater. Echidnas, which are also found in Australia and New Guinea, are covered in spines and use their long, sticky tongues to eat ants and termites.

    Monotremes provide insight into the early evolution of mammals, having diverged from the common ancestor of all mammals around 200 million years ago. Their unique biology helps scientists understand how mammals adapted and diversified over millions of years.

    See more at: https://en.wikipedia.org/wiki/Monotreme ↑

  4. Clarification: Mammals have varying numbers of teats, often corresponding to the typical number of offspring they birth at one time. For instance, cows possess four teats, while goats have two. These teats are located on an udder, which is a prominent mammary structure. In contrast, horses have two teats situated between their hind legs, but these are not as pronounced as the udders found in cows or goats. Therefore, while horses do have mammary glands and teats, they lack a prominent udder. ↑
  5. Explanation: Crop milk is a nutrient-rich secretion from the crop lining of certain bird species, regurgitated to feed their young. It is produced by all pigeons and doves, often called pigeon milk, as well as flamingos and male emperor penguins, indicating the independent evolution of this trait. Unlike mammals, where milk production is usually limited to females, crop milk is produced by both sexes in pigeons and flamingos, and only males in emperor penguins. Controlled by the hormone prolactin, similar to mammalian lactation, crop milk is a holocrine secretion. It contains fat and protein like mammalian milk but lacks carbohydrates. See more at: https://en.wikipedia.org/wiki/Crop_milk ↑
  6. Explanation: A nictitating membrane, also known as the third eyelid, is a transparent or translucent membrane found in some mammals, as well as in birds, reptiles, and amphibians. In mammals, it helps protect and moisten the eye by spreading tears and contributing to tear film production. While it allows some degree of vision, its primary role is protection and lubrication. This membrane is less prominent or vestigial in many mammals, including humans, but remains functional in others. ↑
  7. Explanation: William Fetherstone Montgomery (1797–1859) was an Irish obstetrician and one of the leading medical figures of his time, particularly in the field of maternal and reproductive health. He is best known for his pioneering observations and descriptions of what are now called Montgomery glands, small, raised sebaceous glands located on the areola around the nipple. These glands play a role in breastfeeding by secreting an oily substance that lubricates and protects the nipple during nursing. See more at: https://www.whonamedit.com/doctor.cfm/1470.html ↑
  8. Source: https://www.guinnessworldrecords.com/world-records/112300-most-nipples-on-a-mammal ↑
  9. Explanation: For example, Yale University researchers found that a specific protein halts nipple development in male mice just a few days after mammary tissue begins to form in utero. The protein is parathyroid hormone-related peptide (PTHrP), and it tells the mammary cells to form hormone receptors that attract the male hormones already circulating in the embryo’s blood. Source: https://health.howstuffworks.com/wellness/men/health-tips/why-do-men-have-nipples-brainstuff-video.htm ↑

 

Posted by:

Martin Pollins

Martin Pollins is a Chartered Accountant and MBA with wide experience in corporate finance and business management. He has served on the boards of several companies, including those listed on the London Stock Exchange, AIM and OFEX. He is the Chairman and Founder of OneSmartPlace and was a Council member of the Institute of Chartered Accountants in England and Wales from 1988 to 1996. He was managing partner of PRB Martin Pollins, based in Sussex, the first Accountancy firm to advertise on British television. He went on to create and launch the CharterGroup Partnership (the UK’s first Accountancy network) and then LawGroup UK (at the time, one of the largest networks of lawyers in the UK). In recent years, he helped to raise several £millions to fund British films such as The Da Vinci Code, Bridge of San Luis Rey, Head in the Clouds and Merchant of Venice with actors such as Charlize Theron, Robert De Niro, Al Pacino, F. Murray Abraham. Kathy Bates, Gabriel Byrne, Geraldine Chaplin, Tom Hanks, Ian McKellen, Audrey Tautou, Penélope Cruz, Steven Berkoff, Lynn Collins, Jeremy Irons, Joseph Fiennes and many more. He has written several business publications (see https://onesmartplace.com/resources/)

Leave a Reply

Discover more from The Martin Pollins Blog

Subscribe now to keep reading and get access to the full archive.

Continue reading