this episode is brought to you by curiositystream and nebula where you can watch the first episode of our brand new series becoming human stay tuned to the end of the video for a sneak preview for hundreds of millions of years life on Earth was bound by its medium sea sponges worms and Jellyfish locked inside their watery domain life above the surface would have been inconceivable and impossible for all of Earth's early creatures that is until 440 million years ago when the first creature stepped on to land soon life on terrestrial Earth exploded with all manner
of plants and animals colonizing the globe but even with all this expansion for a long time Earth still had a final frontier a place where no creature had ever gone the sky it's a place that seems so improbable for life to ever exist how can small and random genetic mutations allow an animal to go from completely land-based to Soaring in the skies and yet if you look out your window today you'll see many different creatures that have taken to the skies to avoid Predators or exploit new sources of prey and the more closely you look
at Birds bats and bugs the less similar their flight might seem compare the wings of a dragonfly versus those of a macaw and those of a flying fox the differences are immediately obvious one has scaled Wings on its back another has feathers and the third has webbing stretched between thin bony fingers even more mind-boggling is the fact that the ancient ancestors of all three organisms were wingless and given how Divergent they are on the evolutionary tree we can see that Wings evolved separately three times what's more this particular adaptation even happened a fourth time in
the now extinct pterosaurs the story of these different evolutionary paths has fascinated and befuddled scientists for decades how do such different organisms go from land to Sky it's a question whose answers are still unfolding and it all starts nearly 400 million years ago in the devonian period the early fossil records of insects is extremely scarce and hotly debated among the oldest known of such fossils is rhinyonatha hursty first discovered in Scotland and dating back to around 400 million years it's a very fragmented fossil in which only parts of the head are preserved well enough to
study scientists continue to argue over how to classify it some suggest it's one of the earliest insects to appear others think it should be classified as a millipede and not an insect at all unfortunately the earliest fossil record for insects is sparse and murky in this way there are far more ancestors of arachnids and myropods in the early record than there are insects but this all changed 325 million years ago when the number of insects seemed to explode why because suddenly they were flying the oldest of these flyers looks a bit like an ancient dragonfly
the real mystery is how insects manage to develop those wings in the first place unlike the other flying creatures that we're familiar with today insect Wings didn't evolve from existing arms and it's exceedingly unlikely for organisms to suddenly evolve a whole new body structure did the wings instead come from a pre-existing body structure and if so which ones this question has been one of the major mysteries in biology for decades over time two main hypotheses emerged one is the turgle hypothesis referring to the turgum the top of the insect's body this hypothesis suggests Wings originated
on the insect's backs possibly as membranes for gliding then there's the plural hypothesis suggesting Wings evolved from the side body and began as limbs that folded along the Torso and gradually migrated up to the back the Science World has been fiercely divided over which of these could be correct for years but recently we may have gotten closer to An Answer not by looking at insects but by looking at Crustaceans and arthropods researchers wanted to determine how the seven leg segments of some Crustaceans matched up with an insect's six segments to figure out which segments were
homologous to which in evolution homology refers to similar body parts in different animals due to a shared ancestry sometimes this is obvious a human's left arm is remarkably similar to a cat's left forelimb or even a whale's left fin for example but when comparing insects Crustaceans and arthropods it's not as clear which leg segments correspond to which using a crisper technique the researchers found that insects and Crustaceans legs are homologous if you simply counted the segments from the leg tips in towards the body but what about the Crustaceans seventh leg segment or the eighth leg
segment of an arthropod what part of the insect does that correspond to using genetic Knockouts and gene expression Imaging the researchers realized that the seventh leg segment of crustaceans was in fact homologous to insect pleura its side body while the eighth leg segment of arthropods was homologous to the insect's turgum its top and on top of this they identified Wing genes inside of part of the insect's turgle plate strongly suggesting that insect Wings evolved as outgrowths of the turgum so millions of years ago the eighth leg segment for some became wings and while this debate
isn't fully settled what we do know is that insects evolved flying only once it was such a useful adaptation that they've become among the most successful of all animals they live on every continent and have a stunning array of behaviors and niches to fill perhaps then it's no surprise that once insects an important food source were up in the air the ability for flight began to evolve elsewhere in the animal kingdom the next animals to fly were the biggest flying creatures to ever exist creatures that dominated the skies for millions of years [Music] pterosaurs were
flying reptiles that could be anywhere from the size of a pigeon to the size of a Cessna Aircraft they lived between 225 and 66 million years ago successfully cruising the skies for around 160 million years which is much longer than modern birds have been around while some were astonishingly large most early pterosaurs were pretty small and insectivorous because some species had clawed fingers it was thought that they could climb trees and move about arboreally this led to a few hypotheses for how pterosaurs got their wings the first is the arboreal leaping Theory basically that the
earliest ancestors of pterosaurs hopped around tree branches evolving first to Glide then to fly similar to that was the arboreal parachute model it was essentially the same idea but instead of using extra skin to Glide these creatures would have relied on their arm flaps to catch themselves if they fell out of the trees or jumped to avoid predators lastly there's the ground up Theory this hypothesis suggests that pterosaur ancestors were terrestrial and in their hunting they might have run and jumped to catch prey eventually this led them to develop wings and this last Theory seems
like it might be the most likely according to a recent study scientists recently discovered fossilized tracts from early pterosaurs which showed them to be agile quadrupedal walkers but because pterosaurs had partly hollow bones to assist in their flying ability they didn't fossilize nearly as frequently as dinosaurs so we're left still trying to find answers the fossils we do have show an incredible range of diversity especially for the second half of their existence around that time about 125 million years ago they became even more diverse doubling in the number of species possibly because of the arrival
of more flying creatures ancient Birds [Music] the oldest fossil ancestor of modern Birds is archeopteryx dating back 150 million years ago it was discovered in Germany only two years after Darwin published the Origin of Species and the strangeness of its body contributed a lot to the debate about evolution archeopteryx had an odd mixture of Avian and reptilian features feathers and wings allowed it to fly but it also had teeth and a long bony tail and modeling by scientists suggests that the wing movement was very different from the way we see modern birds fly it would
have moved like a swimmer doing the butterfly strew with the arms coming forward then back instead of the up and down motion of birds flapping their wings today archeopteryx wasn't the first dinosaur to have feathers earlier species did as well even if they didn't have all the adaptations needed for flight that suggests that feathers might have been an adaptation related instead to sexual selection the bright colors could have been a way for the dinosaurs to display themselves to potential mates just like with many modern Birds so if feathers weren't the thing that led to flight
what did like with the pterosaurs the main hypothesis for Avian flight include trees down and ground up one test with winged robots showed that their movement benefited much more when they were gliding than when they were flapping their wings while running which suggests that the benefits of gliding between trees spurred Birds to develop flight another piece of evidence for the tree's down hypothesis was the discovery of microraptor a little dinosaur with four wings that lived about 120 million years ago as researchers studied the anatomy of microraptor they realized its long feathers on its feet would
be a hindrance during running making it unlikely that it could run fast enough for the ground up theory of flight They concluded it was probably capable not only of gliding between trees but also full flight ultimately pterosaurs and dinosaurs went extinct after the meteor crashed into Earth 66 million years ago but birds continued to exploit the skies in the aftermath and their bodies show just how well adapted they are to flight like pterosaurs birds have hollow bones to reduce body weight they also have unidirectional respiratory systems which means air moves mainly in One Direction instead
of moving in and out the way breathing works with humans essentially what happens is that when birds breathe in the oxygen fills sacs around their lungs when they breathe out the air from those sacs is pushed into the lungs this way their lungs are never empty and lacking oxygen this adaptation helps birds get much more oxygen and helps to power their flight but after the meteor Extinction event that killed off the dinosaurs birds weren't the only ones who scrambled to fill the aerial niche they were soon joined by an unsuspecting little mammal the oldest known
bat fossil dates back to 52.5 million years ago it's known as the quad bat because it had claws on all five fingers unlike modern bats which have two claws per Wing at most researchers suggest that having more claws meant this ancient bat climbed around trees and might have even been a quadruped when it wasn't flying another big question with bats is whether they evolved echolocation or flight first scientists have argued over whether this ancient bat had the right Anatomy to allow for echolocation but there haven't been any definitive answers researchers think that the most likely
evolutionary pathway that led to bats being able to fly was that they started out as gliders the question is what led them to Glide between the trees in the first place were they hopping from limb to limb to get fruit or were they chasing down flying insects and if they were chasing insects does that mean they needed to develop echolocation before flight so that they could locate their prey these questions are all still being explored and debated what we know for certain is that bats developed very unique flight characteristics compared to birds the Batwing called
a potagium is formed by skin membranes stretched between the fingers and attached near the ankle it's much more flexible than a bird wing which allows bats a higher degree of fine motor control bats have as many as 25 actively controlled joints in their forelimbs so they can twist their wings into many shapes making them extremely agile Flyers but another difference from Birds is that they have a title biphasic airflow system this is the same type of breathing that we do a breath in fills the lungs with oxygen but when we breathe out the lungs are
empty and just waiting for more oxygen this is much less efficient than Birds unidirectional airflow system not only does it mean bats can't fly as high as Birds where there's less oxygen it might also be the reason why there are some very large flying birds but no enormous bats the largest bat today is the Flying Fox a Genus that includes about 65 species of bat their wingspan can get as large as five feet which sounds pretty big but compare that to the wandering Albatross which has the largest wingspan of the avian family at 11 feet
bats just don't seem to have the right Anatomy to ever grow so large but that doesn't mean they haven't been successful thanks to their wings over 1400 species of bat exist today they account for almost a quarter of all mammal species and they're found on every continent except Antarctica clearly life on the wing is pretty good while bats Birds bugs and the extinct pterosaurs might have found their way to flight through different evolutionary pathways they each discovered an entire new world of possibilities in the sky Evolution teaches us that every possible Niche on Earth can
and will get filled no matter how unlikely it seems and surprisingly the journey to flight and all these animals mirrors our own evolutionary Journey just as flight unlocked a new Niche for so many creatures so too did bipedal movement for our species no longer bound by the inefficiencies of quadrupedal movement early upright humans soon dominated the planet but how did our early ancestors evolve such a unique and honestly strange way of locomotion and what about bipedal movement made our species so unbelievably successful questions like these have swirled in my head for the last few years
on this channel I talk extensively about the evolution of other animals but what about our own Evolution these questions are what led to the creation of our new series becoming human here's a sneak preview when we look at our closest living relatives we are reminded of our particular place on The evolutionary tree it's hard to gaze into the eyes of any of the great apes and not see a reflection of ourselves The Chimps gorillas bonobos and orangutans all resemble us in many ways in both body and behavior but how exactly did we diverge so drastically
from the other primates is it just our big brains that make us so different or something more what were the defining steps in the history of our Evolution that made us the walking talking thinking feeling Society building Apes that we are what were the moments that made us human I wanted to do a deep dive on the subject and break the mold of what our videos normally are I wanted to take our time with it and not worry about what the YouTube algorithm thinks I wanted to focus on the quality the art and the multi-episode
story things that YouTube doesn't always reward you for and for these reasons becoming human is our first nebula original series nebula is the perfect place for us to experiment with new experimental content like this it's our playground for new ideas and right now you can watch the first episode of becoming human over on nebula nebula is the streaming platform made by me and several other content creators as a place for our videos to live at free and without the YouTube algorithm dictating what we should or shouldn't make it's a place full of exclusive original content
from dozens of different creators and signing up is the single best way to support this Channel right now you can watch our previous video about the world's biggest stinkiest and weirdest flower or watch real engineering's latest video about the insane engineering of the Spitfire
