Why do cats, dogs and other carnivores have far neater and straighter teeth than humans? Dan Irwin, Folkestone
Send new questions to nq@theguardian.com.
Readers reply
The better to eat you with. Perchance
My dog used to have perfectly clean teeth but since he won Crufts he’s had a little plaque. Mobilepope
Because they kill to eat meat. To cut the skin and the meat of the animal, their teeth need to be sharp and straight. Manuel (10 years old)
I’ve read that we used to have far neater, straighter teeth and no overbite, but as we began cooking and eating softer food, we chewed a lot less, and over time our jaws became weaker and squashed inwards, causing crooked teeth, etc. Hectormandarin
It is my understanding that the overbite can be traced to the invention/adoption of cutlery, especially the fork. Smaller pieces of food being placed in the mouth prior to chewing, rather than biting and tearing with the teeth, has meant our jaws are weaker and upper and lower teeth are no longer aligned. Mash4077
In fact, cats suffer from misalignment of teeth, known as malocclusion, as much as humans. If domesticated, as long as the cat can bite and chew without the teeth rubbing, they can be left; however, if they prevent normal function, those at fault are removed. In the wild, malocclusion can cause severe problems, impairing the cat’s ability to hunt and eat sufficiently to survive. woodworm20
It’s a case of Darwinism: those with bad teeth would have died out as unable to feed as well, whereas humans can use tools to cut up food. redste
Homo sapiens also have beautifully straight, neat teeth in what remains of their natural environment and within their natural lifespans. Photographs of hunter-gatherers from Papua New Guinea or the Amazon demonstrate this clearly. thebigchil
“Carnivore” as a zoological category only depends on the array of teeth, not dietary habits. We, as primates have four incisors between our “canines” (sorry, dentists, “cuspids”). As we see in the pic of the kitty on top here, “carnivores” have six. So at least one primate is totally carnivorous by habit, the spectral tarsier, whereas bears are generally omnivous, and at least two carnivores are totally vegetarian … the pandas, giant and red. Giant panda is a bear and red panda is a mustelid, like weasels according to recent studies, or possibly a procyonid, like raccoons. SmugglyKanuck
Humans don’t depend on their teeth so much as they use tools to kill and cut up their prey and also to attack one another. An indication that a hominid was a tool user is the absence of large canines (which in apes are used in threat display) and less specialised cutting teeth. letsbeclearaboutthis
I think the gist of the question was really why humans have such a wide range of teeth formations and issues such as underbites and crowding. There are three big factors. First, our skulls got more top heavy and our faces flatter as part of the evolution of our brains and the necessities of childbirth; evolution is an imperfect process. Second, our teeth have over the past 3m years got smaller with thicker enamel due to dietary changes. Humans needed to use our teeth to go from eating fruits and bugs to eating seeds and meat in a relatively short period. Finally, our jaw became pointed, probably because this was selected for more strength for its smaller size. This means our jaws were for a long period under evolutionary pressure to be smaller, pointed, with thickly enamelled tiny teeth. The result of this is a trend of fewer teeth jammed into a smaller jaw, which causes a lot of the common dental problems humans have, but is also the reason we were able to adapt to diets on open plains with big brains. Ultimately, the disadvantages were not significant enough to prevent reproduction and the pressures to have small, pointed jaws was strong enough in contrast, so that’s why we have the dental issues we have. Michael1687
Carnivores don’t just have specialised teeth to slice off and chew meat, they have large molars to crunch through bone. This, as well as eating skin and hair, helps to keep their teeth clean. The longer a lion’s teeth remain in their jaw, the longer they can survive. There are many apocryphal tales of lions with bad teeth turning to easier prey, including humans. trillster
I heard something once about why Britain has a higher percentage of people with crooked or weak teeth compared with other places in the world. More than 350 years ago the British army and navy started using muskets. The gunpowder charge for a single shot was stored in a small sealed cardboard cylinder, and like any military equipment it had to be tough and durable. You needed to tear the top off the cylinder with your teeth, so the army only wanted soldiers who had good teeth. Any man with cavities (or bad or weak teeth) was rejected for military service. Those men stayed home, and bred. The men with good strong teeth served overseas for years and didn’t breed much in Britain, and many of them never came back. That went on for 200 years or so. The men with genes for crooked or bad teeth stayed home and sired many children, the men with good teeth got exported from a young age. Over a couple of centuries, the gene(s) for crooked or bad teeth became more concentrated in the domestic population because of un-natural selection. QuietHillbilly
Unlike people in the UK, who can’t get an NHS dentist’s appointment, fat cats go private. Q5h6f2e39r
Humans are not biological carnivores, as evidenced by almost every aspect of our physiology, and is why we generally need to cook meat before consumption (due to the higher pH level of our stomachs). Our jaws move from side to side like most herbivorous animals, where those of carnivores only move up and down, as most carnivores do not chew their food to any great extent, only tearing the flesh from their prey and swallowing; this likely contributes to their teeth being straighter as there is less requirement for the grinding and chewing done by molars (of which carnivores generally have none of). Alex Smythe
As per James Nestor’s book Breath, humans have crooked teeth due to a reduction in mouth size. This occurred as we moved towards eating much softer foods and stopped chewing as much and as hard. Neanderthals had straight and neat teeth. They had much bigger jaws and chewed much harder, raw food. Cats and dogs and other carnivores never experienced this change in diet. Sam Ajmera
Mama said: ‘Because they got all them teeth, and no toothbrush.’ Mike Reining
I’m studying biological anthropology at university. I can see two interpretations of the question, depending on whether the dental row or dental shape of carnivores is being described as neater and straighter.
If Mr Irwin is more referring to the alignment rather than individual shape of the teeth, humans have a reduced jaw line (reduced facial prognathism) compared with our ancestors, and there is simply less space proportionally for us to grow our teeth into than other animals. As our teeth erupt, the cramped space can cause some people’s teeth to grow at strange angles, which is rare in other species with more prognathic faces. Australopithecus and Homo developed the particularly round shape to our jaws as the prognathism reduced.
Carnivores tend to have relatively small teeth compared with herbivores or omnivores, and have more prognathic faces than us, so they have less material to fit into more space, so their dental alignments tend to be very neat. Some species’ survival can also depend on the front teeth fitting neatly together as that can make killing or restraining prey easier.
If Mr Irwin is referring more to the individual teeth forms with neatness and straightness as terms, very simply, they’re carnivores and we’re not, but that’s not overly helpful.
That question has two parts; why we originally had teeth that are relatively “messy looking” and why we maintained that.
Humans are, of course, primates, and the vast majority of primates are close to obligate herbivores. Because apes evolved from obligate herbivores, we inherited adaptations that fit that. Plant matter is relatively difficult to digest, so it needs to be broken down more in the mouth to allow the stomach to do its job. This means herbivores gain adaptations to make their mouth more efficient at chewing. Increasing the molar size means more grinding surface to break foods down simultaneously, and more surface area to break that food down more thoroughly.
Bigger molars are better for herbivores.
Big teeth are energetically costly to make, so if an animal can get away with not making large teeth, evolution will select for the species to not develop large teeth; smaller molars are better for carnivores.
Primates typically have large canines in a manner like obligate carnivores, but this is a sexually dimorphic trait rather than a feeding adaptation. Males of many primate species compete with each other by displaying their sharpened upper canines. Cats and dogs have them sharpened to eat (as the dagger-like shape is very good for tearing through raw flesh), and to facilitate catching prey.
As early hominins developed reduced sexual dimorphism, they also lost the length of their canines, as developing large teeth is costly and evolution selected against maintaining it.
Canines generally look the simplest, so having relatively small canines can contribute a lot to teeth seeming complicated, and it’s only really the front teeth (canines and incisors) that are straight, so having large canines makes teeth look straighter generally.
The strange many-cusped (Y-5) shape of human molars is pretty rare across the animal kingdom, and is only really an established trait, as far as I’m aware, among apes. I don’t know why that particular shape developed, but it’s fairly clearly a result of increasing the molar abrasive surface, and it’s still useful to us for chewing. This particular shape adds a lot of complexity and “messiness” to the human mouth, especially as some people have additional cusps beyond the normal five for an ape.
So that’s the evolutionary reasoning for why our teeth became relatively complicated compared with carnivores. The reason it stayed like that is because we never changed our diet enough from that for evolution to start changing our teeth in such pronounced ways again.
We’re still primarily herbivores, and biologically we have no real need for meat. It’s fairly well established that early Homo were scavengers when it came to meat; we didn’t need big canines to pull down prey, and because the most nutritious part of the carrion that was left would be the bone marrow, having developed molars is fairly beneficial for the type of predation our ancestors would have engaged in. Further to that, our ancestors developed tools and then fire, so could tailor their food to match what their jaws and dental anatomy could handle.
If you ever want to see what extreme adaptations to herbivorous diets could have looked like in humans, I recommend looking at Paranthropus skulls, particularly P boisei or P aethiopicus. Rachel Buchan
