Dogs
6 Fascinating facts about dogs that you probably don’t know — part 2
I recently wrote an article that promised to surprise you with 6 fascinating facts about dogs. I quickly realized, however, that each fact could easily be an article all by itself! So I resigned myself to splitting the article in 2 parts. So without further ado, here are the 3 remaining facts that I promised in part 1.
4. If you think your dog loves you, you may be right.
Assuming that you’re a dog lover (which you probably are if you’re reading this article), you’ve no doubt experienced a burst of love whilst staring at your dog. And sometimes you may even wonder whether the feeling is mutual… Well the good news is that it may very well be. After many experiments, scientists have defined what is known as the oxytocin-gaze positive loop. You have probably heard of oxytocin, which is widely known as the ‘love hormone’ and works as a neurotransmitter in the brain.
Humans normally experience a surge in oxytocin when interacting with other humans for whom they have affection, especially through eye contact and gazing. The length of the mother-to-infant gaze is directly related to maternal oxytocin. Studies have found that the same phenomenon occurs between dogs and humans. It was found that gazing behaviour from dogs increased the level of oxytocin in humans and dogs alike. Additionally, an initial spike in oxytocin in humans or dogs causes a positive association in the second party, which also raises the second party’s oxytocin level. This is why it’s called the oxytocin-gaze positive loop¹.
However, oxytocin experiments are not the only indication of human-dog bonding. A study conducted in 2014 analysed the caudate nucleus in dog brains using an MRI machine. MRI scans were taken when the dogs were exposed to 5 different smells: themselves, a strange dog, a familiar dog, a strange human and a familiar human (their owner). Only the scent of the familiar human activated the caudate nucleus, which is strongly associated with positive expectations and associations². All-in-all, the evidence that supports dog-human love is not yet definitive but it clearly shows a very strong bond between humans and dogs that may well be love.
5. Dogs have three eyelids
It might sound weird to hear that dogs have 3 eyelids but actually humans are the anomaly. Almost all mammals have 3 eyelids. Humans, and some primates, are the odd ones out with only 2 eyelids. The main purpose of the upper and lower eyelid is to keep debris, light and dust out of the eye. The third eyelid is known as the Nictitating membrane (see Figure 1) and is located in the inner corner of the eye. Upon closing, the membrane moves horizontally across the eye to the top outer corner. The colour of the membrane depends on the breed and health of the dog but is typically black, brown or sometimes pink³.
The membrane is important for a number of reasons. Firstly, it further protects the eye from debris/dust and can wipe away any debris from the cornea (think windshield wiper). Secondly, it helps the eye retain moisture and also has its own tear gland, which is responsible for producing 30–40% of the eye’s tears. Finally, the membrane has the critical job of protecting the eye from infections. The membrane tear gland contains antibodies, and since the cornea does not have any blood vessels, the antibodies are vital for fighting off infections⁵.
6. Dogs were the first domesticated animal
Dogs have been our loyal companions for a very, very long time. They were the first ever domesticated animals and their domestication predates agriculture. The date and location of the first domesticated dogs are somewhat contentious but it is estimated that dogs were first domesticated somewhere between 14,000 and 29,000 years ago and that it most likely first happened in Europe, East Asia or the Middle East. There is also a theory that dogs were domesticated twice (once in Europe and once in East Asia)⁶.
Dogs are primarily descended from wolves and their closest living relative is the grey wolf.
The manner in which the domestication occurred is still uncertain but the main theory postulates that dogs underwent self-domestication and some even go as far as to say that dogs actually domesticated humans. Most likely, the bolder wolves started getting closer and closer to the fire and meat that our hunter-gatherer fore-fathers prepared and the garbage that was left over. Over time, the bold but aggressive wolves were likely killed or driven off by humans, whilst the friendlier wolves were tolerated⁷.
Eventually, this tolerance grew into companionship and wolves even started looking friendlier: ears became floppier and tails started wagging. In addition to these physical changes, their psychology changed too. They started learning our body language and today dogs are even better at reading our body language than chimpanzees (our closest relatives). In fact, a study conducted in 2017 found that domestication changed the facial muscle anatomy of dogs to allow for facial communication with humans. It also found that eyebrow muscle changes have allowed dogs to take on an expression akin to human sadness, which triggers a nurturing response in many humans⁸.
Interestingly, to this day dogs remain the only truly domesticated large carnivore and some even speculate that they may have triggered the civilization of humans. Regardless, the contribution of canines to humanity, and our hearts, is undeniable (cue cheesy music).
That brings us to the end of 6 fascinating facts about dogs. I hope that you’ve enjoyed learning more about our four-legged companions. Stay tuned for more articles on animals… Bumblebees may be next 🐝.
References
- Science|Oxytocin-gaze positive loop and the coevolution of human-dog bonds|Nagasawa, M, et al., 2015
- Elsevier| Scent of the familiar: An fMRI study of canine brain responses to familiar and unfamiliar human and dog odors|Berns G. S., et al., 2015
- USA Dog Behaviour| Did you know all dogs have a 3rd eyelid?|Scheaffer, S., 2019
- MSD Veterinary Manual|Nictitating Membrane
- Vet Organics| Did You Know Dogs Have Three Eyelids?| 2018
- The Atlantic| A new origin story for dogs | Ed Yong, 2016
- National Geographic| Opinion: We Didn’t Domesticate Dogs. They Domesticated Us.| Hare, B, et al., 2013
- PNAS|Evolution of facial muscle anatomy in dogs | Kaminski, J, et al., 2019
