Linnaeus and the Breast

Humans have questioned where we belong in the natural world for centuries. Some still ponder today. Charles Darwin skimmed over the subject very briefly in his wonderful masterpiece On the Origin of Species outlining his theory of evolution through natural selection. Tantalisingly Darwin writes a one liner where humans may fit in; “Light will be thrown on the origin of man and his history”. Darwin’s close friend and supporter, Thomas Huxley, examines in detail the human species compared to other animals in his own masterpiece Man’s Place in Nature (1863). Typical of Huxley’s work, he provides clear and logical comparisons to other species, focusing on apes in particular. To introduce his comparison with animals, always eloquent, Huxley writes;

“The question of questions for mankind – the problem which underlines all others, and is more deeply interesting than any other – is the ascertainment of the place which Man occupies in nature.”

Huxley, Man’s Place in Nature. 1898 Edition. pg 77.

The famous image from Huxley's Man's Place in Nature demonstrating the similarities of the anatomy of the great apes.  (Image from

The famous image from Huxley’s Man’s Place in Nature demonstrating the similarities of the anatomy of the great apes.
(Image from here)

The answer for Huxley’s ‘question of questions’ is surprisingly laid bare in the classification of animals developed 150 years earlier. (Classification is simply organising life. All organisms on the planet are divided into a number of groups which place those with similar features into the same group.*) Of course Huxley talks about classification in Man’s Place in Nature clearly showing us how animals are organised and where humans sit in this classification.

The beginnings of the classification system we use today was developed in the 1700s by a Swedish chap who had a little fondness of breasts. Our story begins long before then, in the heat of the bustling city of Athens where the temples were full, the amphitheatres were packed and the wine filled amphorae were passed round carefree every evening.

Aristotle (384-322BC), the famous Greek philosopher, taught many noble men (including Alexander the Great), and his writings covered a ridiculously diverse range of subjects including politics, music, ethics, poetry and biology.

The great thinker looked at animals and plants and grouped them based on his own observations (looking at the way they move, a little bit of reproduction, and what they are made up of). For the first time, his work grouped animals together based on their similarities. He split the first group into two; ‘Blooded animals’ (basically animals with a backbone; the vertebrates) and ‘Bloodless animals’ (those animals without a backbone; the invertebrates). Aristotle broke the next categories down even further; life bearing (humans and mammals) and egg bearing (birds and fish). The classification didn’t stop there: it went on for some more levels each time grouping animals with similar features so that each time the groups contained less and less animals until it ended up with the individual. The old scholar used his groupings to show a ladder of the simplest organisms moving upwards to the highest, his ‘Great Chain of Being’. Much of this work set the basis for subsequent classification of the natural world.

A lovely marble bust of Aristotle showing rather chiselled features.

A lovely marble bust of Aristotle showing rather chiselled features. (Image from here)

Aristotle’s work on animals and plants stuck around for around 2000 years, before there was a renaissance in looking at the life around us. This mainly began with new attempts at classifying plants because of their important uses in medicines. The Italian botanist, with a rather well trimmed beard, Andrea Casalpino (1519 – 1603) was one of the first to look at the features of plants and use the similarities to classify them. He wrote a somewhat large and, to many people, fairly quite an un-thrilling piece of work describing and classifying over 1500 species based on the structures of the seeds.

Soon after there was an obsession to classify more. Another botanist, this time from Switzerland and a much more elaborate beard, Gaspard (or Caspar) Bauhin (1510-1624) wrote an enormous book on plants. Titled Pinat theatre botanici (Illustrated exposition of Plants), he describes and classifies over 6000 species. Regardless of the slightly limited readership, the wonderful thing about this book was that Bauhin grouped similar plants together, and he introduced the method of using genus and species in his classification; plants which Bauhin thought were similar were placed in the same genus and then each different individual plant was then given their own species name. This method of naming organisms using a genus and species is still used today.

These passionate and mildly obsessed bearded gentlemen had begun to try to arrange life by giving them Latin names. Over the years, there were several attempts with a variety of different groups added and moved around. John Ray (1627 – 1705) was an (unbearded) English man who attempted to classify a huge number of species (over 18,000 plants in one publication!). Ray’s system was thorough but he appeared to combine different characters of different plants in his ‘organising’.

With such a huge variety of different ways in organising life and different names being given to the same plant, there needed to be a standard that would be used the world over. Enter a man who was rather fond of breasts.

Carolus Linnaeus, also known as Carl von Linné, (1707-1778) was a clean shaven Swedish naturalist who gave lectures in botany at Uppalsa University. He had a pure lust for studying as much as he could about the natural world. Linnaeus developed his Systema Naturae (System of Nature) in 1735 as a twelve page list of organising the plants, animals and minerals he knew. His cravings were not satisfied with this work. For the next 31 years he had developed several editions resulting in his monstrous 12th Edition in which he organised and classified over 12,000 different species. All the animals and plants in his Systema Naturae were given binomial names (genus and species) and this set the precedence for future work on naming life. Linnaeus’s system has been widened, adapted and changed over time, but the basic idea is still the same.

Carolus Linnaeus (or Carl von Linné (1707-1778). A Sweedsih naturalist who was well kept and developed the system of classification we use today.

Carolus Linnaeus (or Carl von Linné (1707-1778). A Sweedsih naturalist who was well kept and developed the system of classification we use today. (Image from here)

It is the famous 10th Edition where we get a first glimpse of the breast. Over 2000 years earlier, Aristotle had grouped all animals on four legs as Quadrupedia (including mammals, most reptiles and a lot of amphibians). Makes sense, as they all have four limbs. There were a few problems with the term Quadrupedia which naturalists were not too keen on; for example, manatees only have two ‘hands’, chimpanzees have four ‘hands’, and humans have two feet and two hands. But Linnaeus sorted this out in a little more detail. Along with some classes from the old philosopher, he developed some new ones for his classification resulting in six classes; Mammalia (mammals), Aves (birds), Amphibia (reptiles and amphibians), Pisces (fish), Insecta (insects and arachnids) and Vermes (worms). This allowed for large groups which shared similar features to be grouped in these classes. For example all species of Owls were placed in the same Order (Strix), and this Order was grouped with all other Orders of birds under the Class Aves.

Wonderful. And the link to breasts is in there too. But this will need a little explaining, as it may appear that I have some weird geeky fetish to taxonomy where systematics is the nipple that I enjoy tweaking. Although many of us do get excited about fantastic science, it is not really a fetish. Not really. I don’t have a room fully of pictures of taxonomic trees on my walls in front of a lovely old oak desk covered in pinned insects, study skins and a delightfully old microscope. One day perhaps I will. But for now, my little ‘office’ under the stairs will do.

Linnaeus unveiled the breast in the new class he developed; Mammalia; literally meaning ‘of the breast’. He could have used a different term for this group of animals because there are six little features that you can look at in any animal anywhere that determines whether or not it is a mammal;

  1. An articulated jaw. All mammals have one bone in their lower jaws, the dentary (two dentary bones on the left and right side, which are fused together at the chin). Reptiles have three bones in their lower jaws.
  2. Three ear bones. The lovely little incus, mallus and stapes are the smallest bones in the human body. These three tiny, beautifully shaped bones were once three bones in an early reptilian ancestors head. Three bones, the quadrate, articular and angular in one group of very early reptiles shrank, moved, and became vital in amplifying sound in the animal. This took a long time, and many generations and mutations; each change being useful and passed onto the next generation. We know this because otherwise we wouldn’t laugh and weep at a magnificent performance of the beautiful Madame Butterfly.
  3. Mammary gland. The milk producing glands which are functional in the females and only for a short period of time. This can be with the help of a nipple, or like the platypus and spiny anteater lactating milk on your chest is enough for the little ones to lap up.
  4. The aortic arch (a main artery in the heart) bends to the left. This is a very efficient way of transporting oxygen rich blood round the body as the heart pumps.
  5. Cheek teeth with divided roots. All mammals have the teeth at the back of their mouths (the molars) which have at least two roots holding the tooth into the jaw. Mammal teeth vary for different uses; the flat incisors at the front for nipping grass or flesh; the sharp canines for piercing prey or fighting other males; the pointy pre-molars for slicing or grinding; and the back molars to really slice or grind. Fish, reptiles and amphibians only have the same type of tooth throughout their mouths and one root.
  6. Hair or fur. Mammals are the only animals that have ‘true’ hair which covers their bodies at some point in their lives. The hair grows from skin cells, called follicles, with the little protein keratin.

The term Mammalia derives from the Latin word mammae, referring to the breast or nipple as appose to the actual milk producing glands (the mammary glands). It is interesting that Linnaeus focused on a female feature to name this large group of animals. Some animals in this Class do not have breasts or nipples; such as the wonderfully enigmatic platypus and bizarre quirky spiny anteaters, which are the only living members of the egg laying mammals, the Monotremes. These creatures have all the features of a mammal (three ear bones, single jaw bone, hair, produce milk through mammary glands). But they lay eggs. And they don’t have nipples. (The Monotremes secrete milk from their mammary glands, which the youngsters lavishly lap up.) Because of the features they share with all other mammals, apart from laying eggs, these beautiful creatures do belong to the Class Mammalia.

So really the nipple or breast isn’t actually a defining diagnostic feature of Mammalia. For those mammals that do have nipples, generally both the females and males have them. This is simply because the nipples form in the developing foetus before the sex is developed; for a while in the womb the little developing animal is sexless. (There are exceptions where some male mammals don’t have nipples, for example, horses and some rat species). The true feature of a mammal is not whether it has a nipple or breast, but it is an animal where the females produce milk to nourish their young.

As a little aside, it is delightfully curious that only our species uses the breast for enjoyment during nights of passion. Many women, and men, find the nipple and the surrounding area to be an extremely sensitive and pleasurable part of the body. The amazing and complex evolution of the sex lives of our species is for a future post, but the breast clearly played an enchanting role in our species enjoying and prolonging the sex for as long as we do.

Back to Linnaeus and the breast. Why would he have focused on the breast? He could have easily chosen another term, such as Pilosa (the hairy ones), Aurecaviga (the hollow eared ones), Lactentia (the lactating ones) or Sugentia (the suckling ones), Tresauremos (those with three ear bones), Unamaxillia (one jawed ones). By naming the Class of hairy lactating creatures Mammalia, he created a simple link to include one certain species within his classification; us.

The 10th Edition which saw the introduction of the new term Mammalia, also saw the first time of including humans within the System of Nature; he gave humans the scientific name Homo sapiens. By giving humans a scientific name and including them within his classification, Linnaeus had linked humans with the animal kingdom. Humans were placed along with apes, monkeys and sloths in the Order Primates. (Sloths are no longer within the Primates, but are in a new Order Pilosa along with anteaters.) Of course, there was uproar! Humans in the same group as monkeys!! Oh, to be a fly on the wall as the great scientific folk read this for the first time! But Linnaeus was clever. He showed there was no way out from classifying humans along with other animals; humans share many of the same features as all mammals. One of these features which there was certainly no denying was the breast.

Historically, breast feeding has been seen as linking humans closer to the animal kingdom quite simply because other animals do it, resulting in women seen to be closer to the animals than men. Aristotle noted how women gave birth to live young and nursed their young, just like many other animals. Confused by bodily functions, many people thought that menstruation and lactation were linked; Aristotle believed that the menstrual fluid transformed into the fluid for nursing the young after giving birth. This complete lack of understanding of biology is what we would see today as completely bonkers. Amazingly until the mid-1700s Aristotle’s view on things was believed to be true (that’s 2000 years of silence in the study of science!).

The wonderfully large nipples (or teats) of a female goat with her young close by. The nipples are very large so the baby goat can get easy access. (Image from Wiki: . Image Taken by Fir0002/Flagstaffotos)

The wonderfully large nipples (or teats) of a female goat with her young close by. The nipples are very large so the baby goat can get easy access.
(Image from here)

The choice of the term Mammalia is interesting because the names of all the other groups focus on features shared by all animals in that group. For example, the Phylum Arthropoda means ‘jointed legs’, which all animals (both male and female) in this group have. The Class Amphibia means ‘both lives’ as all these slimy creatures in this group live in and out of water. Mammalia however, focuses on the female of the species. By giving the Class the name Mammalia automatically shows that humans are no different and fit within the classification.

Mr Linnaeus probably thought about breasts for quite some time with this strategic move. With the breast proudly exposed as the defining trait for the group, humans could be included. And here, he was very clever again. He named our species Homo sapiens meaning ‘man of wisdom’ which was a very proud and masculine name. Linnaeus made sure the breast and the woman linked with other animals, and ‘man’ stood alone. Like many in the 1700s, and even 1800s, he still thought that ‘man’ was special, one of God’s greatest creations (Linnaeus himself was a Creationist). So humans fitted in his classification, but were separated from the ‘lower animals’ by the species name he gave. Very clever.

The breast: one defining feature to link humans with the rest of the animal kingdom. Although Huxley’s ‘question of questions’ wouldn’t be asked for another 150 years, Linnaeus had already began to answer it. Linnaeus had wanted to satisfy his lust by organising nature and by doing so he grouped together animals with similar features (ie. animals that were closely related). It was never his intention to demonstrate any evolutionary relationship. His classification however beautifully illustrates the wonderfully diverse tree of life and how all organisms reveal clues to their evolutionary past.

This Class of animals, the beautiful and varied group of mammals, is absolutely extraordinary! One feature in particular is a true marvel of the natural world; sweat glands in one particular part of the body have been modified to produce milk and secrete it through contractions of ducts. Truly remarkable! Only mammals can do this. And this is the real beauty of these creatures. The dinosaurs didn’t breast feed their young; mammals did.  

The Class Mammalia does not demonstrate that women are closer to animals than men – this is an ancient idea that should have faded into dust. Quite the contrary. It shows the importance of females without which the Class would not exist. This is the reason the breast proudly sits so high up, defining this Class of fury, sweaty animals. And quite rightly so. One of the most beautiful features that has evolved in nature has now been immortalised as the defining feature of a very diverse and amazing group of animals we belong to; the mammals.


Huxley, T. H. 1898. Man’s Place in Nature and other Anthropological Essays. New York. D. Appleton and Company.

Schiebinger, L. 1993. Why mammals are called mammals: gender politics in Eightieth-Century Natural History. The American Historical Review. Vol. 98. No 2. pp.382-411.


*The world of organisms is divided into a number of groups which place those with similar features into the same group. All animals belong to the Kingdom Animalia. These are then split into different Phylum (for example, those with a backbone (vertebrates) are placed in the Phylum Chordata). This Phylum is divided into 6 different Classes; all the birds for example are in the Class Aves, and all the mammals in put in the Class Mammalia. Each Class is then divided further with a number of Orders; all bats are in the Order Chiroptera and all cats, dogs, bears, walruses, seals, racoons and skunks are in the Order Carnivora. This is not the end! There is another divide under Order, the Family; this is where the groups become more closed and specialised. For example, all the species of kangaroos are in the Family Macropodidae and al the chimps, gorillas, orang-utans and humans are in the Family Hominidae. The penultimate group level is the Genus. Here there are fewer organisms in this group, sometimes there can be on animal in this group, or sometimes ten. The final group is the species. This is where the individual animal is named, for example all humans belong to the Genus and species Homo sapiens where as all blue tits belong to the Genus and species Cyanistes caeruleus.


Filed under Taxonomy

6 responses to “Linnaeus and the Breast

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