Why are mammals attracted to bad body odors, but humans the opposite?

Friends who keep pets should have discovered that their dogs and cats often go into estrus after smelling the urine of the opposite sex.

Why are mammals attracted to bad body odors, but humans the opposite?

Why is it that when two people are about to take the next step in a loving relationship, people are only put off by bad body odor?

In fact, mammals do not become aroused by "urine", but rather detect signals emitted by the opposite sex through their unique olfactory system.

This hormonal signal means: I am in heat.

Image source: Wikipedia

The unique olfactory systems of animals

Tadpole will first take you to understand how our sense of smell is produced: the smells floating in the air are small molecules. These molecules are inhaled by us through breathing and stimulate the nerve endings inside the nasal cavity (this process is called "complexation").

When the nerve endings sense this stimulation, nerve impulses are generated, which are then transmitted to the "olfactory bulb" in the brain. The olfactory bulb then transmits the nerve information layer by layer to our cerebral cortex, and the brain will react: what kind of smell do we smell?

Image source: Wikipedia

This nasal cavity → brain transmission process is the only way for us humans to produce smell. But for most mammals, they also have a second olfactory system.

The final destination of this olfactory system for odors is called the "accessory olfactory bulb." Similarly, the accessory olfactory bulb is connected by various nervous systems, but the final transmission is not to the ordinary nerve endings inside the nasal cavity, but to the "vomeronasal" at the junction of the nose and mouth of animals.

Image source: Wikipedia

This unique olfactory organ was discovered by a Danish anatomist in 1813. At first, he called it the "vomeronasal organ." 200 years later, as people learned more about it, they gradually discovered that the "vomeronasal organ" is also an organ that cannot "complex" odor molecules in the air like humans do.

Although the vomeronasal organ cannot "complex" odor molecules in the air, it can combine with hormones (also neurokines) in the air. The neurokines released by mammals can precisely reflect their current physical state.

For example, the release of neurotoxins by animals of the opposite sex can indicate that they are in estrus. If they are non-gregarious animals, each time they arrive at a habitat, they can also analyze their physical condition from the hormones released by the previous animal.

As we all know, cats with a strong sense of territory will urinate in their own territory. In fact, this is a way of sending signals, so that other animals can judge whether the "lord" is strong or not through the smell of urine and hormones, and calculate their chances of winning if they fight for territory.

Because humans do not have a vomeronasal organ, they cannot smell these hormones. However, this hormone signal can have a very big impact on animals that have a vomeronasal organ.

In addition to causing the opposite sex to quickly become estrus, if mice smell the cat's urine with body odor, their blood pressure and heart rate will rise rapidly... At this time, their metabolism will speed up to prepare for their escape from this "tiger's mouth."

Why did the human vomeronasal sac degenerate?

For humans, using the vomeronasal nasal cavity to discern estrus information seems incredible. But for animals, we are the outliers because of our degenerated vomeronasal nasal cavity.

At present, the shadow of the "vomeronasal" can still be traced in the early stages of human embryonic development, but after the fetus is fully developed, the "vomeronasal" olfactory system completely disappears... This is evidence that the "vomeronasal" has completely degenerated and disappeared in humans.

In fact, it is not just humans who have experienced the degeneration of the vomeronasal sac, but also crocodiles, aquatic turtles, and birds.

Scientists speculate that the degeneration of aquatic animals may be related to the aquatic environment, while the degeneration of the vomeronasal organ of birds and primates is most likely related to their sensitivity to color.

Similarly, this unique sense of color sensitivity also provides primates with an ability to perceive the world: Is a female gorilla ready to mate? Can't her red and swollen butt tell the truth?

Scent of a Woman

In fact, people also secrete a special smell that attracts the opposite sex, and that is "pheromone".

Pheromones are also called pheromones. They are derived from steroids in the human body and are emitted from sweat glands and the surface of the skin. Female pheromones have almost no smell, while male pheromones are a bit like "body odor."

Many sales websites sell "pheromone" perfumes, which are said to be able to attract the opposite sex...

Well, in order to prevent some naive children from being deceived, Tadpole will explain it to you. Animals cannot speak, so pheromones are a way for animals to communicate with each other using unique chemical molecules, while humans have a unique communication language.

In order to prove whether pheromones have any effect on humans, scientists conducted a series of studies and concluded: yes.

For example, the menstrual patterns of girls living together will gradually become similar, but they do not have the function of attracting the opposite sex as advertised in some small advertisements. Moreover, the "pheromone" perfumes currently on the market are not extracted from human pheromones, but from pig saliva (pig ketone).

Students who have used it all said that it tasted weird.

Well, Tadpole-kun feels weird without even smelling it...

The evolution and degeneration of each species have unique reasons, which is the magic of nature.

END

Reviewer: Wu Lei, practicing veterinarian, Master of Zoology.

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