Learn about whether sharks can really smell a drop of blood from a mile away; how some sharks give birth from two uteruses (and why that’s not even the weirdest part); and the complicated way interstellar travel can mess with language.
Learn about whether sharks can really smell a drop of blood from a mile away; how some sharks give birth from two uteruses (and why that’s not even the weirdest part); and the complicated way interstellar travel can mess with language.
Can sharks really smell a drop of blood from a mile away? by Grant Currin
Some sharks give live birth from two uteruses -- and that's not the weirdest part by Grant Currin
The unintelligible languages of interstellar travel by Cameron Duke
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Find episode transcript here: https://curiosity-daily-4e53644e.simplecast.com/episodes/can-sharks-smell-blood-from-a-mile-away-plus-dual-uterus-sharks-and-how-interstellar-travel-will-change-language
CODY: Hi! You’re about to get smarter in just a few minutes with Curiosity Daily from curiosity-dot-com. I’m Cody Gough.
ASHLEY: And I’m Ashley Hamer. And it’s SHARK WEEK! [cue music] To celebrate, today you’ll learn about whether sharks can really smell a drop of blood from a mile away; and how some sharks give birth from two uteruses — which, spoiler alert! Isn’t even the weirdest part. Then, we’ll head from the sea to the sky, and learn about the complicated way interstellar travel can mess with language.
CODY: Let’s satisfy some curiosity.
Legend has it that sharks aren’t just speed, agility, and teeth. It’s said that they’re also super-smellers who can smell a single drop of blood in the water from a mile away. Buuuut that turns out to be a myth. In reality, sharks are no better than your typical fish when it comes to olfaction. Let’s sniff out this smelly shark myth.
There are a few reasons this rumor has proven so persistent, and one of them comes from semi-scientific observation. See, unlike us, sharks use separate body parts for breathing and for smell. Breathing, of course, happens in the gills. Smell happens in a chamber that’s connected to the outside world by two nostrils, or nares [just like it’s spelled], on the front of a shark’s face.
A shark’s nasal chamber contains a huge amount of tissue with a ton of surface area — way more than other fish. For a long time, scientists thought all that tissue equaled an extremely acute sense of smell.
Researchers put that idea to the test in 2010 with an experiment into how well sharks and their close relatives could actually smell. They analyzed five species: two species of shark, two stingrays and a clearnose skate, which is a fish that kinda looks like a stingray.
One at a time, the researchers subdued each animal with a muscle relaxant and strapped it to a platform suspended in the experimental tank. Then the researchers attached some equipment to its nose: a tube that could deliver scent directly to the nostrils and electrodes to measure signals sent from the nasal cavity to the brain. Then, the researchers filled the smell tubes with various amino acids, which are the building blocks of proteins you might find in blood and animal tissue. It turned out that all five species were equally sensitive to the smells, no matter how much surface area the tissues in their nasal cavities contained. Sharks also did about as well other species of fish that have participated in the same kind of experiment in the past.
Still, they do have an awesome sense of smell — it’s just that when it comes to the fish world, they’re not special. They can’t smell a drop of blood from a mile away, but they probably can from a quarter-mile, or half-kilometer away. That’s about four city blocks.
And that’s just fine. The ocean has a constant, background level of amino acids in the water, and if sharks were smelling all of it, all the time, they’d never be able to focus in on what they want to eat. So no, sharks aren’t super smellers. But they probably like that just fine.
After this next story, you’re never going to hear Baby Shark the same way again. It turns out that shark reproduction is wilder, weirder, and more violent than you’d ever imagine. Starting with the fact that some shark species begin their lives with an in-utero fight to the death. Yeah. Told ya.
I say “in-utero” because many shark species give live birth. That’s pretty odd, since sharks are fish and fish tend to lay eggs. Sharks have eggs too, but they release theirs into a uterus. Scratch that: uteri. That’s right: many sharks have two uteri, where mature eggs are fertilized and develop into baby sharks. And these baby sharks don’t just sit there. Recently, scientists used ultrasound to observe an unborn tawny nurse shark swimming from one uterus to the other inside its mother. And these aren’t the only sharks known to roam their mother’s uterus. Great white and mako [MAY-ko] sharks do the same thing, but they stay in the uterus they hatched in. This might sound adorable, but these shark babies are swimming around for a pretty dark reason. They're feasting on the eggs of their unhatched siblings so they can grow faster.
Ah, but it gets worse! The in-utero life of the sand tiger shark is even more brutal. Multiple free-swimming shark fetuses hatch and fight to the death inside the uterus for the right to be born. This is called siblicide, and it’s not just a shark habit. In fact, a lot of bird species will kill their smaller and weaker siblings in the nest — birds like egrets, boobies, and eagles. The behavior evolves because of food scarcity. For many species, especially fearsome predators like sharks and eagles, there is often not enough food for all of the babies to eat. Siblicide is evolution’s gruesome way of ensuring that at least the strongest of a brood survives.
But scientists think there is an added layer to tiger shark siblicide. See, tiger shark females will mate with multiple males, and this means that the combative uterus-mates may only be half-siblings. That adds an element of genetic competition as sharks from different fathers compete for the ability to eat the unhatched eggs. So even if the mother mates with males of varying genetic quality, only the strongest and most aggressive tend to be born.
Brutal. Maybe “Baby Shark” needs a content warning.
We’re gonna switch gears right now and go from sharks to the stars. If we ever want to travel to another star system, we’re going to have to overcome a lot of challenges. Some are obvious, like dealing with radiation and life support over those vast distances. But some aren’t so obvious. A recent paper by linguistics researchers highlights a problem with space travel that most people don’t think about: the mutation of language.
Languages evolve over time, just like anything else that must be reproduced to survive. If you’ve ever read “Canterbury Tales” you have a sense of what English was like just 600 years ago. It’s changed considerably. Small changes in our language have even appeared in our lifetimes. The word “Internet” wasn’t in the English language, or any language, for that matter, when most of our parents were probably born. Recently, the word “literally” was defined as its complete opposite by the Oxford English Dictionary. Even changes in intonation can alter a language: just think about uptalk, where young people? started talking like this? People who aren’t familiar with it have been known to mistake it for the rising tone of a question, even though linguists say it’s more of a signal of politeness and inclusion.
So language changes naturally, but it changes especially quickly in isolated populations, like settlers on an island or colonists in a generation ship. If the voyage is so long that ten generations of humans are born, have children, and die on the way there, new words and grammatical tendencies will enter common usage on the ship. And it’s not like they’d be keeping up with the language on Earth either, because relaying messages while on a journey to even the nearest star will take years once they’re far enough.
And this evolution, linguists argue, is unavoidable. Even if people were placed on these ships with the sole job of keeping language in a figurative time capsule, they might still be unintelligible to Earthbound humans because language on Earth will be evolving without them, too. To communicate, they might both need to learn a dead version of English, the same way people today learn Latin.
When it comes to communication, interstellar travel will make aliens out of Earthlings.
Let’s recap today’s takeaways
[ad lib optional]
CODY: Today’s stories were written by Grant Currin and Cameron Duke, and edited by Ashley Hamer, who’s the managing editor for Curiosity Daily.
ASHLEY: Today’s episode was produced and edited by Cody Gough.
CODY: Join us again tomorrow to learn something new in just a few minutes.
ASHLEY: And until then, stay curious!