Hank Green: You don't have to be a proboscis monkey or have a pet platypus to know that nature has come up with some pretty fascinating and weird animal adaptations, but in general, the wackier the adaptation is (like blood that works in sub-zero temperatures or having eyes on your arms), the more important its purpose is. Like, "Hey, these things help me find food or survive terrible conditions or help me fight off one of the world's deadliest diseases." I'm Hank Green, and today on SciShow News: new discoveries about weird adaptations -- including in humans -- and the reasons they evolved they way that they did. [intro music] Okay, so first things first. Starfish have eyes on their arms. To be fair, we've known about this for, like, 200 years, but we didn't know until Thursday that starfish can actually use their eyes to see and make decisions about stuff. So, how is it that we knew something had eyes but we never guessed that it could see? Well, because a really important part of being able to see is having a brain, especially the part of the brain that's capable of processing light signals into visual information, like, "Oh, that's a fridge. I'm going to open-- oh, pizza! I am going to eat it." Starfish have clusters of light-sensitive sense called photoreceptors on the tip of their arms, but since starfish don't have brains, we didn't think they had, like, vision, because nature's always like, "And you're going to have useless organs!" But this week, marine biologists from the University of Copenhagen presented a research paper to the Society for Experimental Biology that seems to prove otherwise. The biologists compared the behavior of the starfish species Linckia laevigata, some of which don't have eyes and some of which do. When placed a meter from a coral reef, which is chock full of things starfish like to eat, the starfish with eyes made a beeline for the reef. The starfish without eyes, of course, just kind of bumped around randomly. So, it seems that somehow these creatures don't need a brain to process and understand images. The team thinks these simple eyes are probably a lot like the very first eyes that evolved in the simplest ancient animals, revealing what kinds of tasks probably drove early eye evolution -- specifically, navigating toward large, stationary objects that hold food, like reefs or fridges. Now, what kind of tasks do you think drove the evolution of blue blood in octopi? Answer: Surviving in one of the most hostile places on Earth. Marine biologists from the Alfred Wegener Institute in German presented their research yesterday at the meeting of the Society for Experimental Biology. They studied the protein hemocyanin, which carries oxygen in octopus blood (it's basically the octopus version of hemoglobin), and it contains copper, which is why octopus blood is blue. The biologists compared hemocyanin in octopi living in sub-zero degrees Celsius oceans in Antarctica to that of octopi living in temperate and warm waters, and it turns out that hemocyanin acts differently in sub-zero temperatures than it does in warmer waters. In cold water, hemocyanin goes into overdrive, supplying oxygen to body tissues, keeping the animal healthy, and lightening the load for the octopus's three hearts, which have to work harder in oxygen-rich cold waters. Yes, octopuses have three hearts. The total package means that octopi get to hang out in bitterly cold waters, which is nice because they live short lives and can't migrate very far. So, if an environment gets really harsh, they don't have to move -- they just have to acclimate, and apparently evolution has met that challenge, because today octopi live in virtually ever kind of ocean habitat. Humans, of course, are up to the adaptation challenge as well. We live everywhere. We've done a pretty good job breaking population threshold after population threshold, thanks in part to disease resistance. According to a study released in Thursday's issue of the journal Science Translational Medicine, around 5,000 years ago, people around the Ganges Delta in Bangladesh developed genes that allowed them to survive cholera. The Ganges Delta is the wettest part of the wettest country in the world, and cholera (the bacterium Vibrio cholerae) loves water. Via water, the cholera bacterium infects the small intestine and releases a toxin that causes severe diarrhea, dehydration, and, until modern medicine, usually death. So yeah, avoiding that would have been a pretty useful adaptation. Researchers studied the genomes of 42 Bangladeshi families picked at random, and found 5,000-year-old variants on genes that helped regulate water loss in the intestines as well as on genes that regulate immune responses to infections. Then they looked at samples from more than 200 Bangladeshis who were sick with cholera. They identified 5 especially common gene variants that, when exposed to the cholera toxin in a lab, triggered the production of proteins that aid in fighting infections. Having stuck around for, like, 5,000 years, it's likely that these variants were part of the reason why some people with cholera were able to survive long enough to reproduce, and that's all evolution really wants us to do anyway. So, evolution is awesome. Aren't you glad that you have eyes and blood that works for your purposes and probably some really cool disease resistances? If you have any adaptations that you're particularly thankful for, just let us know about them in the comments below, or you can leave your questions, comments, or tips there or on Facebook or Twitter. And, of course, if you want to keep up to date on all the latest breaking science news, you can go to youtube.com/scishow and subscribe. [outro music]