Transcription
Yes, yes, I know. I said the next video would be the Megalodon paleo profile, but I hit a really big writer's block with that video. So I decided to move on to something else in the meantime. And I kind of wanted to return to making videos on weird biology phenomena, particularly ones related to evolution, which I made several videos on, like my rapid evolution video and my islands video, but with which I'm really proud of how they turned out.
This time, we're gonna talk about another weird aspect of evolution that is visible in almost every aspect of biology. It actually makes a lot of sense when you think about it. Convergent evolution. Ain't nature. There's points where you have to go, "Hey, wait a minute. Wait a minute. I've seen this already." Where evolution gets a little bit lazy with its creatures, and you start to see repeats of the same thing, but at different places and at different times, and most importantly, occurring completely unrelated, independently from one another.
Probably the most famous example of this is the fact that sharks, a type of cartilaginous fish, dolphins, a type of mammal, and ichthyosaurs, a type of reptile, although descending from entirely different backgrounds, developed the same basic body plan of dorsal fin, flippers, and a tail fluke. A good analogy to this is, if I have any SideReel fans out there, man, do I feel old. There's this one episode called "Bizarro Jerry" where one of the main characters finds a group of friends that is pretty much identical to her other friend group. There's the tall weird guy, the short, balding guy with glasses, and Jerry Seinfeld. Well, in a nutshell, that's pretty much convergent evolution for you. Well, kind of.
There are simply too many examples of convergent evolution to list, as almost everything living could have its own convergently evolved counterpart, either still around today or in the past. So I wanted to list the most interesting examples I could find. But before we start, I think the big question is, is why does this happen? Why are there these weird patterns and commonalities that appear in nature entirely independently from one another, that pop up in different times and in different locations?
Well, it has to do with simple physics, natural selection, and the limitation of resources. As most people know, and I think understand, evolution and how animal populations change over time is determined by natural selection. In nature, and the universe in general, there's a common enemy: limited resources. There is never enough food or water or energy to go around all the time. So to combat this, living things on this planet have evolved through natural selection to specialize, to be really, really efficient and good at doing a particular thing.
A fox or a shark has specialized for catching other living things and getting energy for survival, mostly from them. A plant or plankton, on the other hand, has specialized for turning sunlight and other resources in its environment into usable energy. A herbivore or a panda specialized for consuming the plants and get energy from them, and so on. Distinct roles or jobs for organisms in the environment called niches are made. And even within these broad groupings, you can make numerous subgroupings. A fox focuses on smaller animals, while a lion focuses on larger ones. A giraffe focuses on plants at the top of trees, while a horse focuses on plants on the ground. A niche is formed through this competitive process of specialization.
As time goes on, natural selection makes animal populations more and more efficient until the animal is so well-suited for doing its job, the species no longer needs to change that much. The thing is, the limited resources of an environment have to be shared between different organisms. And if two organisms have the same food source, odds are natural selection will cause one to compete the other by trying to be more efficient at gathering that resource than the other. This is called the competitive exclusion principle, which pretty much means that natural selection causes an environment to typically have one species fill one niche. Odds are, I'm probably making this way more complex than it really is.
Let's go back to "Bizarro Jerry." The original Jerry asks if you can hang out with the new friend group, but Elaine says, "We've already got a Jerry." This is pretty much a good analogy for the competitive exclusion principle. There's already a Jerry. Filling the Jerry niche? Well, that's fine and dandy, but that doesn't explain why there's doppelgangers in nature.
Well, on planet Earth, environments are pretty consistent. There's always, until several billion years from now, gonna be a sun and fresh water and salt water and all that, unless something really messes up the Earth. There's always going to be plants and animals and other organisms to use those resources. And because things on this planet stay consistent, so do those niches or roles. Planet Earth is kind of like a big stage play where the roles stay the same, but the characters change. And because of natural selection, as long as there's living things to fill those roles, they will evolve to fit them.
Let's take a look back at the first example. Ichthyosaurs, dolphins, and sharks all share a pretty similar niche in their environment. They're fast marine predators that chase down fish and other smaller marine life. That's their job in the ecosystem. Well, what we find is that typically, there's only one good way to do that job. The most efficient and practical way: having a smooth, streamlined body, a dorsal fin, pectoral fins, and a tail fluke at these locations is the most efficient way to chase down food underwater. It's just a fact. So natural selection and the laws of physics favor animals that have said body plan over ones that do not. It's kind of like that saying, "Great minds think alike." Successful organisms in the same niche evolve alike. Hmm, doesn't really roll off the tongue as well. So essentially, again, it's like poetry.
So if your species evolved to fit your environment and the roles carved out for itself, and if the roles are similar, odds are two things will independently end up with the correct answer. These patterns are just examples of animals finding the right solution to the same problem. They converge towards the same common solution. There's nothing magical or paranormal about it. It's just simple physics. What body plan or body shape works best for this specific job? Times niches are repeated as well, and sometimes different players have to fit the same job.
And here's some really cool examples of this. Probably the most famous examples of convergent evolution is the convergence found between placental mammals and marsupials. The last common ancestor to most modern mammals like elephants, whales, kangaroos, and humans existed probably around the end of the dinosaurs' reign. The ancestors of placental mammals, which includes humans, cats, dogs, bears, whales, and most other mammals today, split from the ancestors of marsupials, which includes kangaroos, wombats, koalas, and so on.
The world at that time looked like this, with many continents not being connected to one another like how they are today. This meant that the placental mammals, mainly on the continents of the northern hemisphere like North America, Europe, and Africa, evolved independently from the marsupials of the continents of the southern hemisphere like South America and Australia. This isolation allowed two groups to evolve to fit their corresponding niches. Largely, this meant that the marsupial moles of Australia dug deep underground, never competing for worms against the placental moles of North America, Europe, and Africa. Or the marsupial thylacine never competed for smaller mammals with the placental fox or wolf.
Although many of these animals look very similar, they are not closely related to one another than we are to dolphins. Actually, they are less related to one another than we are to dolphins. The convergence is actually startling when you look at how similar some of these animals evolved to look and act alike. The thylacine evolved to resemble canines like wolves and foxes so much that at Oxford, when zoology students were required to identify 100 animals just based off their skulls, it became widely known among students that if they saw a dog-looking skull in the exam, odds are it was a thylacine. The thylacine skull resembled a dog so much that when teachers caught wind of the rule, they replaced the thylacine skull with an actual dog skull. And let's just say students did not have a good time that year.
So, I don't know if you ever end up in this oddly specific situation, but one of the few and easiest ways to tell the difference is the fact that thylacines, like most marsupials, have two distinctive holes in their palate bone. That thylacines are not all. Basically, every placental had its own bizarro marsupial version. For example, moles appear to have both convergently evolved with mole crickets. Wolves and anteaters, gliders, and so on. They got to the point in which a close relative of the marsupials convergently evolved saber teeth and a cat-like body to resemble the placental saber-toothed cats.
Convergent evolution isn't just visible in present-day. There's actually a lot of convergence that occurs in the past. Dinosaurs, in particular, convergently evolved with a lot of animals. There are actually many parallels to be made between the non-dinosaurian reptiles of the Triassic, who preceded the dinosaurs and then were horribly wiped out in a mass extinction, and the post-Triassic dinosaurs, who would replace them. In a manner almost identical to placental mammals and marsupials, back in the Triassic, we had the crocodilian-like phytosaurs, the heavily armored quadrupedal desmatosuchus, and the dome-headed triceratops. Believe it or not, all of these animals are not dinosaurs, but they did have dinosaurian counterparts: the crocodilian-like Spinosaurus, the heavily armored Ankylosaurus, and the dome-headed Pachycephalosaurus, all evolving such features independently from one another.
Mammals of today kind of echo the ancestors of mammals of old. In the Permian, the world was largely dominated by synapsids, or what are commonly known as mammal-like reptiles. They weren't dinosaurs or even closely related to lizards or crocodiles or turtles. They were, in fact, closely related to us and shared many traits with us. They, as some evidence suggests, might have even possessed hair, making the similarities between early synapsids and mammals even more obvious. Just like with the saber-toothed mammals of later days, synapsids had their own saber teeth. With therapsids, and very interestingly, there appears to have been strange tree-dwelling precursors to monkeys or raccoons or squirrels with their own opposable "thumbs" evolved literally hundreds of millions of years before our own. One can only wonder if these thumbs, tree-dwelling creatures might have convergently evolved even more with mammals and had their own synapsid apes and monkeys using their hands for things other than climbing trees. Oh, Permian mass extinction, why did you have to do what you did?
Individual organs, as opposed to body plans, can convergently evolve as well. The eye appears to actually be a very simple and easy thing to evolve, as it has happened several times independently. From the compound eyes of arthropods to the four eyes of the box jellyfish (yes, they have eyes, and it's creepy) to the countless eyes of scallops to the countless single-celled organisms that create "eyes" within their bodies. Vertebrates like you or I and cephalopods like squids and octopuses actually have independently evolved almost identical eyeballs, both equipped with lenses, retinas, and irises. With the only real big difference between the two is the fact we have this awful thing called a blind spot, in which there's an area in our field of view where it's literally just a blank hole, which our brains have to subsequently account for and fix. Something those lucky squids don't have, because unlike us, whose eyes evolved as outgrowths of our brain, their eyes evolved out of the surface of their skin. Darn squids with their flawless eyeballs.
The thing is, convergent evolution is so common that within humans ourselves, there's examples. Open human races or skin colors can be seen as an obvious example of convergent evolution, as it appears light skin colors have evolved at the very least twice in humans, in Europeans and East Asians, and maybe even a third time in the prehistoric indigenous Japanese. It may be even a fourth time if you count Neanderthals. Independently from one another, humans originated from sub-Saharan Africa, and due to this, in our original state, our ancestors possessed darker skin colors, probably to protect our skin from sun damage and skin cancers. However, as various human groups migrated to northern latitudes, it seems at the very least the lineages that became Europeans and East Asians developed lighter skin colors, probably due to the obvious advantage of it maintaining vitamin D3 production in the skin more efficiently than darker skin. The two populations apparently changed skin color independently from one another, and this is reflected in the difference in the genes and mutations responsible for this trait in the genetic makeup between the two populations.
The list of convergences goes on and on. From swordfish like the Xiphias to stingray like the Plakodonts to stork like the Pterosaurs to mantis like grasshoppers. Similarities just repeat and repeat and repeat, regardless of time or place. It's kind of amazing and beautiful to see that patterns and commonalities arise within life, even though they're often separated by millions of years. It makes you wonder just how many bizarro versions of animals today existed in the past, and if everything we see now will just keep on repeating and repeating as it has for eons until the end of life on Earth.
And this brings me, probably one of my absolute favorite examples of convergent evolution, and the primary motivation for this video. This is a sea slug. And this is one of the few but very beautiful pictures that I could find of this truly bizarre and alien creature. It's a type of sea slug, close relatives to snails you typically see crawling along the sea floor. This particular branch of sea slug gave up its life as a bottom-feeder and started to live its life in the open sea, swimming with its own tail fluke, dorsal fin, and even pectoral fins. Right from its typical sea slug horns, the resemblance is uncanny to that of a fish. This animal, slimy, boneless, with bioluminescent translucent skin, whose ancestry couldn't be more unrelated and alien to the backbone fish, has nonetheless converged towards the same body type design.
Could we ourselves be a niche that can just be filled in? Could intelligent species building tools, just like saber-toothed and shark-like body plans, just be filled by different characters throughout time? It's kind of reassuring when you think about it. If we all died in a mass extinction and almost everything was wiped out, there'd still be hope for the future, and that we'd all be replaced with bizarro versions of ourselves. Life can hit the reset button and start all over again, and it's been doing this time and time again. Extinction, sometimes it's just the beginning of a new chapter of the same story, with similar roles, only with different actors. Who knows what the future or the past has in store? All I know is that a safe bet is is that all the animals of tomorrow or yesterday might resemble those of today, only if you squint really hard.
And on that note, thank you so much for watching my detailed examination of convergent evolution. I hope you guys enjoyed this video, and I'll hopefully get that Megalodon video out soon. If not, the next one is the Behemoth video, where I'll wrap up that last video I made. And expect a teaser trailer of some kind very soon. All right, see ya.
"Señorita, I'm in trouble again and I can't get free."
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