For a dentist, the narwhal’s smile is a mystery of evolution (2012) | Hacker News Reader

For a dentist, the narwhal’s smile is a mystery of evolution (2012)

insider.si.edu

66 pointssohkamyung19 comments

I'm no biologist... but the person quoted in the article doesn't seem to understand that some things are explained by natural selection and some things are explained by sexual selection. The tusk doesn't have to have a purpose.

“The whole thing that is great about the teeth of the narwhal is that nothing makes sense,” Nweeia adds. “The tusks are an extreme example of dental asymmetry. They exhibit uncharacteristic dimorphic or sexual expressions since females do not exhibit erupted tusks as commonly as males. Also, the tusk has a straight axis and a spiraled morphology. Conventional mechanisms of evolution do not help explain these expressions of teeth.”

From Wikipedia:

https://en.wikipedia.org/wiki/Sexual_selection

Sexual selection can, typically, lead males to extreme efforts to demonstrate their fitness to be chosen by females, producing sexual dimorphism in secondary sexual characteristics, such as the ornate plumage of birds such as birds of paradise and peafowl, or the antlers of deer, or the manes of lions, caused by a positive feedback mechanism known as a Fisherian runaway, where the passing-on of the desire for a trait in one sex is as important as having the trait in the other sex in producing the runaway effect.

https://en.wikipedia.org/wiki/Fisherian_runaway

As another example, musical talent is probably an example of "Fisherian runaway" in humans. It doesn't make a person more likely to survive, but it makes a person more likely to mate.

The key point is that music can be broadcast to a large audience. And the audience can instantly tell if the music is "good" or not. It can't be faked.

You make patterns of noise that indicate 1) working sensory perception 2) motor skills 3) cognitive skills like memory and 4) the ability to cooperate with other humans (i.e. a band).

Hence it indicates fitness. It's selected for sexually, but not "naturally".

(edit: Now that I google it, it seems like a lot of scientists think that too (including Darwin), which is not surprising. It seems hard to prove, even though it makes a lot of sense.)

Eh.. you're going to have to provide something other than a constructed "just so" story to get anyone to believe that musical talent has been specifically selected for. It's not impossible, but it's not at all obvious either.

At the very least it is weird that the article says nothing about sexual selection, it is the go to hypothesis (that of course subsequently requires proof) for weirdness. Like a peacock's super unhandy tail. Or the building of blue nests and performing weird dances in them by certain birds. If evolution lead to apparent wasting of energy, it is almost certainly sex related.

But I guess it is a mystery of evolution to a dentist. Maybe said dentist (Martin Nweeia) should talk to an evolutionary biologist before appearing in blogs.

It's also not like the Narwhal somehow decided to not have teeth, I guess if you swallow fish whole and everything is fine, a Narwhal without teeth has more energy left and less tooth related problems and thus better survival.

Humans are moderately complex, so we have multiple means of demonstrating fitness rather than just one. But there's plenty of evidence that successful public music performance is highly attractive to at least some of the population. (Noodling around with a DAW in your spare bedroom doesn't count.)

I vividly remember reading a site in India which explained how expertise in one particular style of drumming was "considered useful in marital selection."

In the 18th and 19th centuries, musical skill could literally be a deal maker for eligible women looking for a husband.

And groupies are definitely a thing - certainly once you get to the stadium sell-out and/or internationally known DJ level.

It's even rumoured that killing a karaoke session will get you admiring looks.

(Etc.)

Probably tells you have working coordination and memory etc.

Things like poem or speech recitals used to be more common too before.

The fact that a trait is sexually attractive isn't good evidence that it's present as a result of sexual selection.

A performing musician has several desirable traits that may preclude being a musician if absent. Given the phenomenon of groupies wanting to sleep with musicians I would not be surprised if musical ability is currently being selected for.

Another of their own articles, linked at the bottom [0], hints at both sexual selection and natural selection:

> Usually, only males grow a single tusk, suggesting that it may have a function in sexual selection. Females judging the suitably of mate by the size of his tusk, horn or body mass is a common trait among animals.

> Recent research demonstrating a statistical link between the length of a male narwhal’s tusk and the size of its testes would seem to support this theory, except there is one hiccup: female narwhals can grow tusks too.

> The tusks may be used by males like the lances of jousting knights to demonstrate their dominance, scientists say. Forehead scars seen on male narwhals and broken tusks may be evidence of such battles. Narwhal “jousting” has never been documented in the wild yet recent video footage from a drone has captured for the first time narwhals appearing to “stun” fish with their tusks.

> Beyond mating, scientists are finding increasing evidence that narwhals may use their tusks to sense their surrounding environment and help catch prey. New research has provided indications that the tusks may have the ability to sense the temperature and salinity of ocean water.

[0] https://insider.si.edu/2018/02/meet-worlds-weirdest-whale/

Differentiating between natural and sexual selection feels pretty hand wavy to me (also not a biologist.)

Your hot-guy rockstar example perfectly illustrates how sexual selection is natural selection. If something is super attractive but also interferes with breeding, it’s not going to have a lasting impact on a species (if it’s genetic).

What’s the fitness here of the tooth-horn?

If you're a rockstar and have 3 kids by 22 it doesn't matter if you die at 22, 24 or 98. You propagated your genes and been more successful than the average man (that only has 2 offspring). Survival that does not lead to reproduction is pointless from an evolutionary perspective.

BTW they also use their tusks to hunt/stun fish: https://news.nationalgeographic.com/2017/05/drone-footage-na...

My understanding is that the definition of evolution is the changing of statistics of phenotype/genotype in a population. So, how many children you have is just one way to measure your influence. How many grandchildren would be another, and note that you could have children without any of them having children. If you influence anyone that shares some of your genes, then you're not "pointless from an evolutionary perspective". If you save your cousin from drowning, you've increased the probability of genes you share of being passed on. If you invent chemical fertilizer that allows billions of people to be fed, you have massively influenced the propagation of many of the genes you share. If you help develop policy or a political movement that affects how disabled people are treated, that's not outside of evolution. Etc.

Tiniest, tiniest of nits to pick - sexual selection is natural selection.

Well, those who distinguish the two do so on the basis of "natural selection" describing the process of being more fit for survival in an environment and so having more offspring survive compared to competitors, vs being able to out-compete in providing more offspring in the first place.

So, yeah, having more surviving progeny by means of social dominance (sexual selection) can be considered a form of natural selection, but it's through internal rather than external forces. It's a useful distinction.

I would say that sexual selection one of the mechanisms of natural selection.

Natural selection is more properly distinguished from selection by domestication.

> The strap-toothed whale, for example, has two teeth that wrap over its upper jaw preventing the animal from opening its mouth.

A weird animal I'd never heard of until reading this article!

Just saw this too! Amazing!

> They exhibit uncharacteristic dimorphic or sexual expressions since females do not exhibit erupted tusks as commonly as males.

Sexual dimorphism is common in the ocean (at least with fish). Is dimorphism unheard of in mammals (eg whales)?

I wonder if they meant with regard to teeth, since I assume for mammals that use teeth the way we do dimorphism would be less common or less extreme

Random but fun tangent: browse through some of the identification books by Paul Humann. Many fish have different traits in their juvenile, adult, and sometimes terminal phases (e.g. the spotted drumfish is breathtaking in JP and much less in AP). They can also change color. Memorizing these fish for scuba diving sometimes feels like prepping for the LSAT.

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