Februari 23, 2017
stated clearly presents: what is the evidence for evolution? the theory of biological evolution makes twovery bold claims about living creatures: first: all living things on earth are related.they evolved from a common ancestor. second: the evolution of living things ispowered by natural processes. things which can be studied and understood. but is there really any evidence that thesetwo claims are true? yes. there are so many observable facts fromso many different fields of study that the only way we can even begin to talk about themis to group them into categories or lines
of evidence. to keep things simple, here we’ll focuson evolution’s first claim that: all living things on earth are related. we cannot tackle the entire tree of life atonce (after all there’s an estimated 8.7 million species alive today), so instead we’llfocus most of our attention on one fairly small but fascinating branch of the evolutionarytree: cetaceans. this branch includes whales, dolphins and porpoises. biologist claim that all these creatures areclosely related, and that the entire group evolved from an ancient 4 legged land mammal.
instead of taking their word for it, let’slook at the facts. we’ll start with a few from field of comparative anatomy: the studyof differences and similarities between living things. whales live in water and from a distance,they sort of look like giant fish. a close inspection of their anatomy however, tellsus a very different story. whales, just like land mammals but unlikefish: have placentas and give live birth they feed milk to their young they are warm blooded (which is extremelyrare for a fish)
and whales do not have gills, instead, justlike us, they breath air with 2, fully developed lungs. whales don’t seem to have noses like mammalsdo. instead they breathe through blowholes coming out the tops of their heads. some whaleshave two blowholes that almost look like nostrils, but dolphins and porpoises only have one.surprisingly, if you look at their skulls, you find that the blowhole splits into 2 nasalpassages inside the head. could it be that the blowhole is actually a highly modifiedmammal nose? it looks that way but we’ll need more evidence to be sure. many whales have hair, just like land mammals.in this photograph, you can actually see the
whiskers of this baby gray whale as he restshis chin on mama's back. strangely, whales have arm, wrist, hand, andfinger bones inside their front flippers. here’s a photo of these bones, the samebones that bats, hippos and people have in their front appendages: one bone, two bones,wrist bones and finger bones. modern whales do not have back legs but theydo have a pair of strange tiny bones where the hips and hind legs should be. here’sa picture of these bones from a bowhead whale. they almost look like shriveled hip, thigh,and shin bones. this one even has what looks like a deformed ball and socket joint betweenthe hip and thigh bone, just like the ball and socket joint in your own hip. is thisresemblance a mere coincidence or are these
real leg bones? perhaps leftovers from thewhales evolutionary history? before we draw any bold conclusions, let’ssee if a completely separate line of evidence will confirm our suspicions. embryology is the study of how creatures developbefore being born or hatching from an egg. here we see a dolphin and a human embryo,side by side, at similar stages of development. notice that they both have what look likearm buds, and leg buds. in humans, the leg buds grow to become legs. in whales, theygrow for a while, but then stop, effectively fading away as the rest of the whale continuesto grow. these are all photographs of a common dolphinat different stages of development. notice
that early on, we see two nostril grooveson the front of the face, just like you’d expect in a puppy or a human. as the dolphin continues to grow, the nostrilgroves migrate to the top of the head and fuse together becoming the dolphin’s blowhole. so far we have multiple facts from two independentlines of evidence, comparative anatomy, and embryology, both telling us the exact samestory: the ancestors of whales were once 4 legged land creatures! will the fossil recordact as a third witness confirming this idea? these are two species of extinct basilosauridwhales! these creatures are known from multiple wellpreserved skeletons. they appear to have lived
side by side roughly 34 to 40 million yearsago. in this photo we are looking down at the topof a basilosaurid skull. this is not a model or a cast, these are the actual bones whichwere pulled from the ground. notice that the nasal opening is not on the top of the headlike those of modern whales, and not at the end of the snout like those of most land mammals.instead their nostrils sit right in the middle, this is an intermediate species, exactly whatthe theory of evolution tells us we should find! at the back-end of a basilosaurid’s body,there are small, yet fully developed hips, legs, ankle, feet and we suspect they hadat least 3 toes though we’ve only found
the bones for one. these legs are far too small for walking onland, but may have been useful for mating or scratching away parasites and itchy skin. evolutionary theory tells us that the furtherwe go back in time, the harder it will be to distinguish whales from regular land mammals. meet maiacetus. scientists have found multiplewell preserved skeletons of this species, one of which appears to be a pregnant mother. the hip bones of maiacetus do seem sturdyenough to walk on land, but this animal is considered to be a whale for many reasons:their skeletons have all been found among
fossils of sea-creatures their short legs combined with long flat fingersand toes, suggest they were strong swimmers with webbed hands and feet. here we see the bottom side of a maiacetusjaw and skull as it looked at the dig site. her teeth match those of the basilosauridwhales we saw earlier. and unique structures of her middle ear bones,the bulbs behind her jaw, match those of basilosaurid whales and modern whales. maiacetus appears to be, a walking whale! the fossils of many ancient whale-like mammalshave been found, and people continue to find
more. together, these fossils blur the linebetween 4 legged land mammals and fully aquatic whales, solidifying the idea that whales indeed,evolved from land creatures. now lets look at a 4th line of evidence: dna? dna molecules contain chemical codes whichact like recipes for living things. without ever looking at bones, embryos, oranatomy, researchers can compare the dna code of different living creatures to find outwho is most closely related to who. whale dna has been compared to all kinds ofother animals: fish, sea lions, you name it, and so far, the closest genetic match, isto the pudgy, water-loving hippopotamus. this does not mean that whales evolved fromhippos, but if this genetic finding is correct,
whales and hippos both evolved from a commonancestor which lived roughly 54 million years ago. at first the link between whales and hippossurprised researchers. whales are mainly carnivores - they eat things like fish and small crustaceans,while hippos are mostly vegetarian. a closer look however, reveals that hipposand whales, actually share many strange features, some of which may have come from their commonancestor. ancient walking whales have specially shapedankle bones, found only in hippos and the close relatives of hippos, hippos, just likewhales, often give birth and even nurse their young underwater, they both have multi chamberedstomachs (which is common for herbivores but
unheard of in fish-eating mammals), they areboth missing a coat of fur, and here’s a fun fact - whales and hippos are some of theonly mammals on earth that have internal testicles. so there you have it, dozens of facts from4 independent lines of evidence, all tell us the exact same story, whales evolved from4 legged land mammals, but the history of whales isn’t the only evolutionary historythat we’ve been able to work out. we know from fossils, dna, embryology andmany other lines of evidence that bird wings are actually modified arms and claws! birdsevolved from dinosaur-like ancestors. we can also clearly see that bat wings evolvedfrom 5 fingered hands, similar to those of monkeys and shrews.
we’ve found that humans share a fairly recentcommon ancestor with chimpanzees, that mammals evolved from reptile-like creatures, thosereptile-like creatures evolved from amphibian-like creatures, those amphibian-like creaturesevolved from fish-like creatures, and fish if you go back far enough, share a commonancestor with segmented worms. so to sum things up, thousands of observablefacts from completely independent fields of study, are coming together to tell us theexact same story. all living things on earth are related. i’m jon perry and that’s a basic overviewof the evidence for evolution, stated clearly. thanks for watching our show, if you enjoyedit, be sure to share it with your friends
on facebook and twitter. if you want to learn more about whale fossils,and who doesn't, we have links in the description of this video which take you to articles onour website. special thanks to tyler proctor, zaid ghasib,anthony danzl, leon z newman, rosemary mosco, and jordan collver. all of these folks volunteeredtheir time and talents to make this animation happen. special thanks to dr. philip d. gingerichand dr. hans thewissen. they both volunteered hours of their time advising us, and preparingimages of fossils and embryos. i'm proud to announce that for the first timein stated clearly's history, this animation
was completely paid for with contributionsfrom our viewers. if you are able to help support our please visit us at statedclearly.comand click "contribute" so long for now, stay curious.
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