Are Humans Mammals?

It’s easy to take for granted the fact that humans are mammals. If a primate is a mammal and a human is a primate, logic would dictate that a human is also a mammal. Yet, what makes a mammal unique? Are humans mammals? Why do we think of humans as different from other mammals, and even other primates? These are all questions that might come to mind as we explore the features of the mammal, the primate, and the human.

Features of Mammals

All mammals are vertebrates in the class Mammalia. Mammals give birth to live young which they suckle with mammary glands that secrete milk. All mammals also have three middle ear bones, a neocortex region in the brain, and either hair or fur. Humans have all of these characteristics. These features distinguish mammals from the other vertebrates, which are reptiles and birds. However, they all belong in the Amniota clade, meaning the young gestate inside an amniotic sac and are without a larval stage.

Yet, some mammals are so unusual we question the features that classify them as such. Most other mammals give birth to live young, but the platypus lays eggs. While it has fur and the female feeds milk to its young, it sweats milk instead of excreting it through teats or nipples. It’s also one of the few mammals that produce venom.

Marsupials are mammals, but they are not placental mammals. Placental mammals have an organ called the placenta that provides nourishment and oxygen to the young developing in the uterus. Marsupials give birth to underdeveloped offspring. They carry the young inside of a pouch, which has several teats that secrete milk. Although some mammals may seem very different, they have all the major hallmarks of class Mammalia.

Features of Primates

The order of Primates includes all land-dwelling eutherian mammals. Eutherian means that the young are developed within the body of the mother. It is believed that the first primates lived in trees. Later descendants evolved to walk and live on land.

All primates have large brains, intelligence, dexterous hands, a shoulder girdle, collarbones, and forward-facing eyes with visual clarity and color vision. Many primates, but not all, have full or “true” opposable thumbs. Whereas non-human primates have hands on all four limbs, humans only have hands on their arms. So, which characteristics do humans and primates share?

Are Humans Really Mammals? Why or Why Not?

As discussed in the beginning, humans are a type of primate, and a primate is, indeed, a mammal. Primates include humans, apes, monkeys, chimpanzees, lemurs, tarsiers, and lorises. It is generally believed that humans shared a common ancestor with the chimpanzee and diverged 6-8 million years ago. We often use the term, “non-human primate” to refer to primates that are considered animals.

Like other mammals, including primates, the human female gestates its young in an amniotic sac. The mother provides nourishment through the placenta, gives birth to live young, and feeds them milk. Like other primates, the human has dexterous fingers, opposable thumbs, a large brain, intelligence, a collarbone, a shoulder girdle, and forward-facing eyes with visual clarity and color vision.

In terms of the brain, what humans have in common with other mammals is that they have a neocortex. This region is used for higher-order functions such as sensory perception, language, coordination, and spatial reasoning. The neocortex is part of the frontal lobe. In fact, the mammalian brain is divided into three different regions and is often called the triune brain, which came about as a result of vertebrate evolution.

What Makes Humans Unique?

What distinguishes the human from a non-human mammal isn’t the species. In fact, the modern human only has a 1.2% genetic difference from the chimpanzee and a 1.6% genetic difference from the gorilla. Humans, bonobos, chimps, and African great apes have a 3.1% genetic difference from Asian great apes, including the orangutan. There is also genetic diversity between humans in a specific population, as well as between the various human races.

The brain is the most important difference between humans and primates. Compared to other primates, humans have much larger brains relative to their body size, which indicates more advanced cognitive abilities. The human neocortex is also larger in proportion to the rest of the brain when compared to non-human mammal brains. This results in more complex functions, creativity, self-awareness, and fine motor control. Humans also have complex social structures, as well as more sophisticated language that cannot be matched by non-human primates or any other mammal.

Conclusion

We learn from an early age that humans are mammals, but we don’t know all the reasons why. The features that make humans similar to other mammals are important, as it is common to believe that humans are completely different from non-human animals. Humans may be at the top of the food chain, and we may have created civilizations, but all mammals share a number of things in common. So, are humans mammals? Yes. A human is a unique creature, but it’s still a mammal.