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Evolutionary Arms Race Between Plants and Caterpillars Created Mustard

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If you're a fan of mustard, wasabi or any other savory flavors that come from plants in the order Brassicales—cabbage, horseradish, kale or mustard—you have caterpillars' distaste for those exact flavors to thank for their existence. 

Some 90 million years ago, ancient Brassicales plants evolved to produce chemicals called glucosinolates as a defense against the cabbage butterfly caterpillars that were decimating the vegetation. This key component of mustard oil not only tasted bitter to the bugs, it was toxic for them—making it the perfect defense, at first. But over the course of the next 10 million years, the caterpillars, in turn, evolved a protein that allowed them to digest the chemical defense. This gave them a new food source all to themselves. The cabbage butterflies flourished and evolved into several new species, all with the ability to eat mustard oil plants.

Needing a new defense, the plants' evolution added in different amino acid ingredients to make new glucosinolates that allowed them to branch out into more species. And while that worked for a little while (you know, hundreds of thousands of years) you can probably guess what happened next.

This back and forth over the millennia was essentially an evolutionary arms race during which a pair of species pushed each other to keep up. The coevolution of cabbage butterflies and Brassicales plants has been known about for a while. But for a paper published this month in Proceedings of the National Academy of Sciences, a group of scientists led by J. Chris Pires, a plant evolutionary biologist at the University of Missouri, made a pair of evolutionary family trees. When they lined the two trees up, they noticed that the branching of the different species corresponded perfectly to the opposing group's new genetic feature. They were able to infer that they were not simply evolving alongside one another but in direct response to each other.

This worked out well for humans, who now enjoy a range of cruciferous vegetables that evolved from those ancient cabbage plants when the family tree expanded, and which get most of their flavor from the glucosinolates that originally developed to ward off caterpillars.

"Why do you think plants have spices or any flavor at all? It's not for us," Pires told NPR's The Salt. "They have a function. All these flavors are evolution."

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All of Your Teeth Evolved From a Single Ancestral Tooth in the Age of the Dinosaurs
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Anyone who's received a root canal or a lecture from their dentist about flossing probably doesn't appreciate their teeth like they should. But our pearly whites are unlike any other structures in the body, and for that, they deserve some recognition.

In their new video, TED-Ed explains what exactly makes teeth unique. Unlike regular bones, teeth are made of two layers: a hard enamel coating and a strong dentin core. The combination of these two components makes teeth both hard and strong enough to endure a lifetime of wear and tear.

The tooth's tough composition isn't exclusive to humans. All mammals, whether they're meat-tearing cats or grass-munching cows, grow their teeth the same way, and they owe their teeth's existence to a common ancestor.

In the 19th century, paleontologist Edward Drinker Cope hypothesized that the tribosphenic molar, a tooth type that evolved during the dinosaur age, is the root of all modern mammalian teeth. With just a few genetic tweaks made over millennia, the tribosphenic molar has given way to the teeth used by carnivores, herbivores, and omnivores to process their food.

To learn more about the evolution and biology of teeth, check out the video from TED-Ed below.

[h/t TED-Ed]

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Stones, Bones, and Wrecks
The Most Complete Fossil of an Early Human Relative Goes on Display
AFP, Stringer, Getty Images
AFP, Stringer, Getty Images

Twenty years after it was discovered in an African cave, one of the most important fossils in the quest to demystify human evolution is finally on display. As Smithsonian reports, Little Foot, an Australopithecus specimen dating back more than 3 million years, was revealed to the public this month at the Hominin Vault at the University of the Witwatersrand’s Evolutionary Studies Institute in Johannesburg, South Africa.

Paleontologist Ron Clarke discovered the first bone fragments from the fossil in 1994. The pieces came from the remains of a young female’s feet, hence the nickname. Clarke and his team spent years excavating Little Foot bit by bit from the Sterkfontein cave system in South Africa until the bones were fully removed in 2012. The shattered remains had been embedded in a concrete-like material called breccia, making them incredibly tricky to recover. But the sum of the parts is monumental: Little Foot is the most complete Austrolopithecus fossil known to science.

The hominid genus Austrolopithecus played an essential early role in the chain of human evolution. Lucy, another famous hominid fossil, is a member of the same genus, but while Lucy is only 40 percent complete, Little Foot retains 90 percent of her skeleton, including her head. It’s also possible that Little Foot surpasses Lucy in age. Most paleontologists agree that Lucy lived about 3.2 million years ago, while one analysis places Little Foot’s age at 3.67 million years.

Austrolopithecus is believed to have spawned Homo, the genus that would eventually contain our species. The discovery of Lucy and other fossils have led scientists to designate East Africa as the cradle of human evolution, but if Little Foot is really as old as tests suggest, then South Africa may deserve a more prominent point in the timeline.

Following Little Foot’s public debut, the team that’s been studying her plans to release a number of papers exploring the many questions her discovery raises.

[h/t Smithsonian]

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