Learn about common ancestors shared by every human; evolution’s multiple directions; and universal facial expressions. There's a point in the past when every person on Earth was an ancestor to every person alive today by Grant Currin Hershberger, S. (2020, October 5). Humans Are All More Closely Related Than We Commonly Think. Scientific American. https://www.scientificamerican.com/article/humans-are-all-more-closely-related-than-we-commonly-think/ Hopkin, M. (2004). Human populations are tightly interwoven. Nature. https://doi.org/10.1038/news040927-10 Numberphile. (2019). EVERY baby is a ROYAL baby - Numberphile [YouTube Video]. In YouTube. https://www.youtube.com/watch?v=Fm0hOex4psA Rohde, D. L. T., Olson, S., & Chang, J. T. (2004). Modelling the recent common ancestry of all living humans. Nature, 431(7008), 562–566. https://doi.org/10.1038/nature02842 Evolution Doesn’t Have Just One Direction by Ashley Hamer Is the human race evolving or devolving? (1998, July 20). Scientific American. https://www.scientificamerican.com/article/is-the-human-race-evolvin/ Waimanu, the first penguin. (2010, January 30). March of the Fossil Penguins; March of the Fossil Penguins. https://fossilpenguins.wordpress.com/2010/01/30/waimanu-the-first-penguin/ Morber, J. (2016, October 6). 5 Times Evolution Ran in “Reverse.” Science; National Geographic. https://www.nationalgeographic.com/science/article/reverse-evolution-explained-hagfish-penguins-snakes-science?loggedin=true Elliott, K. H., Ricklefs, R. E., Gaston, A. J., Hatch, S. A., Speakman, J. R., & Davoren, G. K. (2013). High flight costs, but low dive costs, in auks support the biomechanical hypothesis for flightlessness in penguins. Proceedings of the National Academy of Sciences, 110(23), 9380–9384. https://doi.org/10.1073/pnas.1304838110 How Birds Lost Their Teeth. (2014, December 12). Audubon. https://www.audubon.org/news/how-birds-lost-their-teeth The evolution of whales. (2021). Berkeley.edu. https://evolution.berkeley.edu/evolibrary/article/evograms_03 How did whales lose their hind legs? - Popular Mechanics. (2006, May 23). Popular Mechanics. https://www.popularmechanics.co.za/science/null-610/ Are facial expressions universal? by Ashley Hamer (Listener question from Jared in Vancouver) Price, M. (2016, October 17). Facial expressions—including fear—may not be as universal as we thought. Science | AAAS. https://www.sciencemag.org/news/2016/10/facial-expressions-including-fear-may-not-be-universal-we-thought Ekman, P., & Friesen, W. V. (1971). Constants across cultures in the face and emotion. Journal of Personality and Social Psychology, 17(2), 124–129. https://doi.org/10.1037/h0030377 Crivelli, C., Russell, J. A., Jarillo, S., & Fernández-Dols, J.-M. (2016). The fear gasping face as a threat display in a Melanesian society. Proceedings of the National Academy of Sciences, 113(44), 12403–12407. https://doi.org/10.1073/pnas.1611622113 Krys, K., Melanie Vauclair, C., et. al. (2015). Be Careful Where You Smile: Culture Shapes Judgments of Intelligence and Honesty of Smiling Individuals. Journal of Nonverbal Behavior, 40(2), 101–116. https://doi.org/10.1007/s10919-015-0226-4 Follow Curiosity Daily on your favorite podcast app to learn something new every day withCody Gough andAshley Hamer — for free!
Learn about common ancestors shared by every human; evolution’s multiple directions; and universal facial expressions.
There's a point in the past when every person on Earth was an ancestor to every person alive today by Grant Currin
Evolution Doesn’t Have Just One Direction by Ashley Hamer
Are facial expressions universal? by Ashley Hamer (Listener question from Jared in Vancouver)
Follow Curiosity Daily on your favorite podcast app to learn something new every day with Cody Gough and Ashley Hamer — for free!
Find episode transcripts here: https://curiosity-daily-4e53644e.simplecast.com/episodes/are-facial-expressions-universal
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. Today, you’ll learn about that time when every person on Earth was an ancestor to every person alive today; and why evolution doesn’t just have one direction. We’ll also answer a listener question about whether facial expressions are universal.
CODY: Let’s satisfy some curiosity.
Lots of people can trace their ancestry many generations back. But how far back would you have to go before you found one ancestor who was related to everyone alive today? A million years? A billion? Try 3,500 years ago.
How can that be? Well, the math gets a little tricky, but the basic idea is simple. You are 1 person, you have 2 parents, 4 grandparents, 8 great grandparents. Take that same pattern back 33 generations and you’d expect to be the direct descendent of more than 8 billion people. That’s the power of exponential growth, baby.
But that theoretical calculation has a big problem: there have never been 8 billion people on Earth at the same time. The entire global population 33 generations back was about 300 million. That’s a measly 4 percent of the ancestors you supposedly had alive at the time.
So what’s the deal? It turns out that you have a bunch of ancestors who you’re related to in multiple ways. Maybe your great, great, great, great grandmother on your grandfather’s side was also your great, great, great, aunt—and was also your great, great, great, great, grandmother on your great-grandmother’s side.
In the words of a researcher who studied this question, humanity is, quote “incredibly inbred” end quote. So inbred that every single one of us is the direct descendant of a single person who lived between 1400 BC and 55 AD. That person is a great, great, great, great [is there a sound effect to convey the passage of time that could go here?] great grandparent to every person on Earth today.
The bad news is that it’s... a little icky. The good news is that we’re all cousins! Woohoo!
Something even more interesting happens if we go back a bit further in time. See, that person we were just talking about is our most recent common ancestor. That means all of their ancestors are also our common ancestors. When mathematicians started thinking about that family tree, they discovered something fascinating. At some point between about 5000 BC and 2000 BC, every person alive at the time fell into one of two categories. Either their lineage would eventually die out, leaving them with no living descendents today. Or they would become an ancestor common to everyone alive today. If their line continued to the present, it means that every single person on Earth, from Shanghai to Chicago to Sao Paulo, is their greatgreatgreat grandchild.
None of this is intuitive, but it’s important. We’re all one big human family — even if we don’t... always act like it.
In everyday language, the words “evolution,” “progress,” and “improvement” pretty much mean the same thing. But when it comes to biological evolution, things don’t always work that way. It’s just as possible for an organism to evolve new features and abilities as it is for an organism to lose them. That’s what some people call “reverse” or “regressive” evolution. You probably shouldn’t, though, and I’m gonna tell you why.
By definition, any change in the genes of a group of organisms is evolution — for better or for worse. The idea that lungs are better than gills or opposable thumbs are better than paws comes from centuries-old beliefs about humans being the pinnacle of evolution. But the truth is that we’re just one result of millions of adaptations that help organisms survive their environment to bear offspring. If circumstances make it so an organism with flippers produces more children than one with feet, that organism’s population thrives. Match point, evolution.
Maybe the most obvious example of so-called “regressive evolution” is the penguin. If you go back far enough in the penguin’s evolutionary tree, you’ll find a bird that can fly. Fossil evidence shows that penguins lost the ability to fly more than 60 million years ago, and recent studies point to why: as their wings became more efficient tools when diving for prey, they became less efficient at getting them off the ground.
Evolution always comes at a cost — you can be good at swimming, you can be good at flying, but you usually can’t be both. Still, the inability to fly opened the door to other adaptations. Penguins got bigger, which made them better at withstanding the cold, and their bones got denser, which kept them from immediately floating to the water’s surface. Penguins didn’t “devolve,” they just got really good at what they do best.
There are plenty of other examples — snakes once had legs, for instance, and birds once had teeth — but most surprising might be the fact that the whale’s ancestors started in the sea, evolved legs and walked on land, then went back into the water and lost them again. At each step in the evolutionary chain, these unique adaptations helped the organisms eat more, live longer, and have more babies.
Think about it this way: whales share an evolutionary ancestor with the hippo, which kept its legs. Watching the way each live in their respective environments, you’d never say the hippo is “more evolved” than the whale, would you? I hope not.
We got a voicemail! Have a listen.
[VOICEMAIL]
Great question, Jared! In fact, scientists have been wondering that very thing for more than a century, even back to Darwin’s time. The first big answer came in 1971 from psychologist Paul Ekman. He visited isolated cultures, like those in Papua New Guinea, to find out. He would tell his participants a story, show them pictures of Westerners with different facial expressions, then ask them to choose the emotion appropriate to the story. His results seemed to demonstrate that yes, facial expressions are universal. From happiness to anger, people in these isolated cultures saw each face as expressing the same emotion as Westerners did. That research is now almost universally accepted, and can be found everywhere from college textbooks to those “how are you feeling” posters in kindergarten classrooms.
But that’s not the end of the story. In 2011, psychologist Carlos Crivelli and anthropologist Sergio Jarillo also visited an isolated culture in the same region — but they stayed there. They learned the language, took clan names, and embedded themselves in the local culture. And when they performed a similar experiment with their new friends, the results were more mixed. The participants matched a smiling face to happiness almost every time, but they couldn’t agree on which emotion was conveyed by a scowl, a scrunched nose, a pout, or a neutral expression. But they did agree on one: a wide-eyed gasping face — one Westerners would associate with fear — was almost always associated with anger.
That’s far from the end of this debate, and more research is sure to come. But you might notice one thing that’s similar in both studies: a smile always means happiness. There’s more to that story, too. Studies have found that even if a smile is happy around the world, different cultures have different opinions of smiling people. And they’re not all good. In places like Russia, Iran, Japan, and India, a smiling person is seen as unintelligent. And in cultures with more corruption, a smiling person is seen as less trustworthy.
So, like many things in human behavior, this one doesn’t have a simple answer. But one thing’s for sure: if you’re going to smile in a foreign country, read up on the local culture first. Thanks for your question, Jared! If you have a question, send an email or a voice recording to curiosity at discovery dot com, or leave us a voicemail like Jared did at 312-596-5208.
CODY: Before we recap what we learned today, here’s a sneak peek at what you’ll hear next week on Curiosity Daily.
ASHLEY: Next week, you’ll learn about how dinosaur bones are like tree rings;
That time people panicked about electricity in the 1800s;
Where we got the names of our planets;
How quickly people’s brains adapted to having a robotic “third thumb”;
And more! Okay, so now, let’s recap what we learned today.
[ad lib optional]
ASHLEY: The writer for today’s first story was Grant Currin.
CODY: Our managing editor is Ashley Hamer, who was also a writer on today’s episode]
ASHLEY: Our producer and audio editor is Cody Gough.
CODY: Have a great weekend! SMIIIIIILE LIKE YOU MEAN IT... Then, join us again Monday to learn something new in just a few minutes.
ASHLEY: And until then, stay curious!