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Paranthropus was an offshoot of human evolution that lived alongside us ~2 million years ago. Despite ultimatley going extinct, it remains my favourite branch of human evolution because it’s just so weird. And I’m not the only one who thinks that. When Mary Leaky found one of the more complete skulls it was quickly nicknamed “Nutcracker man” based on its strange jaw and teeth.

The one, the only, nutcracker man

However, it turns out that name may have been a bit premature. Not only because didn’t they eat many nuts, but their teeth aren’t all they cracked up to be (haha, get it?).

This twist comes from a study on the southern species of this lineage, Paranthropus robustus. Researchers found their teeth were riddled with defects, to the point where the authors, Towle and Irish, concluded it couldn’t have been an accident. P. robustus actually evolved weak teeth1.

The pitfalls of Nutcracker Man

The defects in question are a series of tiny pits covering the crowns of most P. robustus teeth. On the surface, these wouldn’t be anything to worry about. However, they can provide a home for plaque and other things, dramatically raising the risk of dental carieses and tooth decay, ultimately weakening the teeth1.

Not the sort of thing you want to happen if you’ve got a reputation as a nutcracker.

Pits on 4 P. robustus teeth

We know the pitfalls of these defects (haha) because they do sometimes occur in people. Typically, they’re the result of stress during growth, like lack of food or ingesting nasty compounds, mucking with the development of the tooth. Basically, these stresses turn off the cells making the enamel, leading to these holes in it1.

However, Towle and Irish weren’t sure that this could explain the defects they foun in Paranthropus. For starters, they’re way more common than you’d expect. These sorts of interruptions to tooth development only impact the tooth growing at that time. Consistently undernourished people can wind up with more of these defects, but never quite so many: Paranthropus had these defects in 47% of milk teeth and 14% of permanent teeth, compared to 7% and 4%, respectively, seen in other species1.


The weirdness of Paranthropus‘ defects don’t end there. These pits are also unusually even, having a similar size and spacing across the whole tooth. This consistency also extends across sites, with Paranthropus fossils from across South Africa showing a similar level of pitting. Unless every single Paranthropus in the region had the exact same diet, something was up1.

The genetics of nutcracker man

After all of this, Towle and Irish were faced with a bit of a paradox. Paranthropus teeth had defects that looked like they stemmed from malnutrition, but nothing else about them fitted with that explanation. They were just too common and consistent.

Fortunately, that weirdness could hold the answer. After all, genetics can make things common and consistent. Could these pits be the result of evolution? Perhaps mutations made them much more vulnerable to these defects cropping up.

Now, it might seem weird to think a species would evolve a tendency towards defects. However, it’s worth remembering that evolution isn’t some all knowing force with a grand plan. It can have “unintended” consequences that, as long as these downsides don’t outweigh the benefits of a change, will persist.

These are technically called “pleiotropic effects”, and humans are riddled with them.

Sickle cell disease is the classic example of pleiotropy. If you have one copy of the gene it confers a resistance to malaria. Two copies also add a blood disorder into the mix. The gene persists because the pleiotropic effect is rare enough (with kids having a 1/4 chance of inheriting it) that it doesn’t outweigh the benefits of the malaria resistance.

In the context of Paranthropus, the evolved big chonky teeth with thick enamel. Could one of the mutations responsible have a pleiotropy that makes them vulnerable to pitting? Genes linked to enamel thickness are also associated with an increased risk of pitting in modern humans. And as long as those pits don’t outweigh the benefits of chonk, both conditions would continue1.

So, nutcracker man serves as yet another reminder that not every trait in human evolution is there for a reason. Sometimes, evolution is just messy.


  1. Towle, I. and Irish, J.D., 2019. A probable genetic origin for pitting enamel hypoplasia on the molars of Paranthropus robustus. Journal of Human Evolution129, pp.54-61.

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Tom B · 14th March 2019 at 2:03 am

“Sometimes, evolution is just messy.”

One more nail in the coffin of “intelligent design”. Even if you buy the fantasy of “design”, it was clearly not very intelligently done.

    Adam Benton · 14th March 2019 at 5:23 pm

    Which always makes the fact they moan about not being taken seriously super hilarious. Like, they clearly haven’t even gotten over the first hurdle of presenting an argument that can’t be dismissed on the face of it.

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