The Planetary News Radio – Episode 6: Supernovae and Bipedalism in Humans

Hello. Welcome to the Planetary News Radio Episode 6. Some good news. This podcast is now available on the iTunes store and the Google Play Store. Granted, I know I don’t have a lot of listeners right now, but if at some point in time in the future, a future listener finds this recording they can now use iTunes and Google to listen to other future recordings. So that’s good for future people. What about past past people, or past hominids? Humans being a group of apes that walk upright consistently specifically, really, modern humans and their direct ancestors that are not chimpanzees. There’s an article in the news, or several articles about a recent study done on hominid evolution, [specifically, on the evolution of bipedalism (walking upright)].

The evolution of walking upright is always a controversial topic, along with most of the topics in human evolution. Intelligence, bipedalism, opposable thumbs for being a very generalised species in terms of diet and living conditions. Humans have a couple or really multiple, very specific adaptations. They give us an advantage, bipedalism, being one of those intelligence being another one. Although intelligence is more recent than bipedalism. That’s a common misconception that humans intelligence is linked with bipedalism. It really isn’t. The first Hominins that walked up-right didn’t have larger brains than chimpanzees, or rather, the shared common ancestor of chimpanzees and humans had a brain the size of a chimpanzee, but bipedalism was important. We don’t know why, [and scientists] struggle to understand why. There’s lots of theories. Some of them makes sense. Some of them don’t. Some of them make more sense than others.

For example, the need to see over tall grass is obvious, and it seems important. The question is, “How strong of a driver of selection would that be”? Is that enough to basically create a whole new lineage of hominid? I think a more interesting theory [for a strong driver towards bipedalism] is the ability to carry things, because if you’re quadrupedal, in order to walk, you can’t carry anything. You might be able to lumber along with one thing in one arm, like a gorilla. Gorillas can carry a child or some food in one hand while lumbering along with the other hand, like people, and maybe they can do brief bouts of bipedalism. Chimpanzees, gorillas, orangutans, and a lot of monkeys can walk bipedally for something out of time. Usually, when they’re doing that, they’re either doing a threat display, they’re about to fight something or trying to scare another animal, trying to make themselves look bigger, or they’re carrying something (food or a baby). So I think, in terms of strength of [natural] selection, historically, that’s been a really good theory. And you see the evolution of opposable thumbs going in line with bipedalism, and then the enlargement of the brain is later.

So, really, humans are these apes that got really good at carrying things. Now, in the news today, there’s a trending article, and so why am I talking about this? So there’s a new theory that supernova could have made humans walk up, right, study says. And so I’m going to read the title of the article. “A massive supernova could have made humans walk upright”. Okay, How so? Let me read another title. “Walking upright evolution of bipedalism linked to supernova”. In new theory, this is very attention grabbing again. Ironically, what is the attention grabber here? Space. Supernova. A giant explosion in space. Let me read another another title. “Exploding stars led to humans walking on two legs, radical study suggests”.

Now let’s say that I stopped there and I didn’t read any of these articles or keep reading titles. And I just left with the idea that a star made humans walk upright. How could that be? I can’t imagine how that is possible. My first instinct is that what they’re trying to say is that people wanted to look up at the star and that’s why they walked upright. That wouldn’t make sense. There’s not enough selective pressure for that to be the case, so right off the bat, because of what I know about evolution, I dismissed that idea, and this seems like fake news, maybe, or just bad reporting.

If we keep reading [though, we eventually see a useful title], “Ancient supernova prompted our ancestors to walk upright to avoid forest fires”. Well, now I’m interested because that is something I didn’t think of, and it has a strong selection pressure because in order to avoid fires, that’s a life or death scenario. So in terms of natural selection, that makes a lot of sense. Natural selection, avoiding forest fires. That’s plausible. That’s strong. So I like this idea. I’ve only read the headlines. So how could supernova cause forest fires, though? Just using my own knowledge of physics and science, and ions were mentioned one of the headlines. Something about ions. So I suppose when a supernova happens and sends out a blast of radiation, material, solar dust, and in that material are ions, charged particles. When those particles get to the earth, they get through the atmosphere and they impact on the surface of the Earth. How did they cause forest fires? My suspicion is that the charged particles don’t actually cause fires themselves.

How can ions cause forest fires? I suppose if you had a stream of charged particles impacting on a forest they might do a couple things and my sense is that what it could do is make that forest drier, more brittle, and so maybe it’s increasing a fire risk. And so what you’re what you’re experiencing is a landscape altered by the supernova, causing increased fire risk. Now, [in terms of selective pressures], not only do you have the benefit of being able to carry things, giving you an immediate benefit, you have the pressure of avoiding fires, and so between avoiding fires and carrying food that could help explain why bipedalism evolved so quickly and recently, relative to the entire evolutionary history of primates, which is around 40 to 50 million years. True bipedalism only evolved recently.

Now this does become problematic because there are other vertebrates that evolved bipedalism, the obvious case being dinosaurs and birds. So the question is, do we think that bipedalism could only be caused by forest fires? Are there other reasons that animals could evolve bipedalism? Let’s think about this logically, we know the dinosaurs evolved bipedalism and that they did not have opposable thumbs. So, in other words, dinosaurs weren’t carrying things yet they evolved be bipedal. So we have two reasons. We think, bipedalism evolved 1. To carry things and 2. To avoid forest fires, and we know for a fact the dinosaurs didn’t need to carry things. So we know that bipedalism must have evolved for at least one other reason then we suspect, which means that it might also evolve for many other reasons, sort of like the Drake hypothesis with finding life on other planets. If we find life on even just one other planet, the probability of finding life on many other planets increases exponentially. So how strong is this theory [of bipedalism]? Well, we’ve already proven that there’s other reasons why things could be bipedal because the dinosaurs are bipedal [not all bipedal dinosaurs] lived in forests, so they couldn’t have been avoiding forest fires. So now we know there are other reasons that animals could evolve bipedalism. So what does this mean for this theory? What does it mean for dinosaurs?

Now, I feel more curious about why dinosaurs evolved bipedalism. Now that I’ve thought about this through. So what else is inherent to bipedalism? Something about bipedalism, that’s shared between primates and dinosaurs, that doesn’t involve a forest doesn’t involve carrying things. What do dinosaurs and apes have in common? Well, apes don’t have tails. Dinosaurs do have tails. So it’s not a tail. They have a torso, a head, and a neck. They’re both social. That’s interesting. Dinosaurs and apes are both social animals. We know this because find evidence of nesting behavior with dinosaurs. So the origin of bird nesting [probably originated from their therapod dinosaur ancestors]. We know dinosaurs have a lot of vocalization adaptations, [for example in hadrosaurs where] we’ve found the enlarged nasal passages [that most likely were used for either mating or herd control].

[Both primates and dinosaurs are social, so could there be a social reason for bipedalism?]. [Maybe yes, if there were some social benefit to bipedalism]. Could a dinosaur communicate just as well if it were bipedal. [Take hadrosaurs for example again]. Hadrosaurs are vegetable eaters, not a carnivore. A hadrosaur does have some decently sized arms. It actually can get down on all fours, so hadrosaur can go back and forth between quadrupedal and bipedal. It’s not like a T. Rex. A T. Rex has almost completely lost its arms almost down to just little tiny fingers, so T. Rex cannot be quadrupedal. Hadrosaur can. So what’s the advantage there? Well, if a hadrosaur is dependent on eating plant material, some of that material might be from a marsh or a swamp. Some of that material might be from a tree. So if you’re bipedal you can stand on your two legs, you can reach up and get higher branches. You can reach down and get algae from a swamp, and you don’t need arms to do that. You just need a mouth. So the hadrosaur shuffling through a swamp [can reach food from the ground, like algae, and branches from trees, by standing on its hind legs].

So what about humans? Makes sense. Food. If you’re foraging for food, you need to be able to reach up, to find more fruit and reach down find roots and vegetables. [It gives animals an option to reach higher or lower places without having to grow an extended neck like a Brontosaurus or Giraffe]. So there’s a new reason to bipedal: Reaching food. I like that. So this is an example of how I like to solve evolutionary problems. We have the question initially – Is this a good hypothesis? Humans avoiding forest fires. That makes sense. It seems possible. Is it the only reason that humans evolved bipedalism? Probably not. It’s probably one of five, or more, major reasons. And I’m just guessing that because I know I talked about three [hypotheses] here. And so there’s probably more that we don’t know about that we haven’t thought about. So that’s the thing with evolution, there’s usually multiple reasons why things evolved, and so this is not a criticism [against this particular evolutionary hypothesis].

I did find that information about the forest fires from the titles, but about four out of five of the articles did not mention the fire. They just mentioned the supernova, and so it’s a little misleading in terms of a headline, but it’s not really purposely misleading. So I wouldn’t call this fake news. That’s just sensationalism. So sensationalism isn’t that bad. It gave me something to talk about it [and explain how using the scientific method can be applied to determine how plausible an idea is without doing any extra research]. I hope you enjoyed this talk. That’s Bryan White with The Planetary News Radio signing out. Thanks for listening. Have a good day.

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