For millions of years, life on Earth was confined to the oceans, with creatures like sea sponges, worms, and jellyfish thriving in their aquatic habitats. The idea of life existing on land seemed impossible until about 440 million years ago, when the first organisms began to explore terrestrial environments. This marked the beginning of a massive expansion of life on land, with plants and animals spreading across the globe.
Despite this terrestrial expansion, the sky remained an unexplored frontier. The idea of life taking to the air seemed improbable. Yet, if you look outside today, you’ll see numerous creatures that have mastered the art of flight, using it to escape predators or find new food sources. Birds, bats, and insects all have unique methods of flying, each adapted to their specific needs and environments.
When you compare the wings of a dragonfly, a macaw, and a flying fox, the differences are striking. Dragonflies have scaled wings, macaws have feathers, and flying foxes have webbing between their fingers. Interestingly, the ancestors of these creatures were all wingless, and wings evolved independently in these lineages. This adaptation even occurred a fourth time in the now-extinct pterosaurs.
The evolution of flight has intrigued scientists for decades. How did such diverse organisms transition from land to sky? This question’s answers began to unfold nearly 400 million years ago during the Devonian period.
The early fossil records of insects are sparse and debated. One of the oldest known fossils is Rhyniognatha hirsti, discovered in Scotland and dating back around 400 million years. Its classification is still debated, with some suggesting it is an early insect, while others argue it might be a millipede.
About 325 million years ago, insects began to fly, leading to an explosion in their numbers. Unlike other flying creatures, insect wings didn’t evolve from existing limbs. Two main hypotheses emerged: the tergal hypothesis, suggesting wings originated as back membranes for gliding, and the pleural hypothesis, proposing wings evolved from side limbs that migrated to the back.
Recent research using CRISPR techniques has shown that insect wings likely evolved as outgrowths of the tergum, a part of the insect’s back. This discovery suggests that millions of years ago, some insects developed wings from an eighth leg segment, leading to their incredible success as a group.
Pterosaurs were the first vertebrates to achieve powered flight, living between 225 and 66 million years ago. They ranged in size from small, insect-eating species to massive creatures with wingspans rivaling small aircraft. Several theories exist about how pterosaurs developed flight, including the arboreal leaping theory, which suggests they evolved from tree-dwelling ancestors, and the ground-up theory, proposing they were terrestrial runners that developed wings to catch prey.
The oldest known ancestor of modern birds is Archaeopteryx, dating back 150 million years. This creature had a mix of avian and reptilian features, contributing significantly to the debate about evolution. It had feathers and could fly, but also possessed teeth and a long bony tail.
Modeling suggests that Archaeopteryx used a wing movement similar to a swimmer’s butterfly stroke. Feathers may have initially evolved for purposes other than flight, such as sexual selection. Theories about avian flight include the trees-down and ground-up hypotheses, with evidence suggesting that gliding between trees may have been a precursor to powered flight.
After the extinction of pterosaurs and many dinosaurs 66 million years ago, birds continued to thrive, and bats soon joined them in the skies. The oldest known bat fossil is about 52.5 million years old. Bats have unique flight characteristics, with wings formed by skin membranes stretched between their fingers, allowing for greater flexibility and control.
Bats have a biphasic airflow system, which is less efficient than the unidirectional system of birds. This may explain why there are no giant bats like there are large birds. Despite this, bats have been incredibly successful, with over 1,400 species found worldwide, except in Antarctica.
The evolution of flight in insects, pterosaurs, birds, and bats demonstrates the incredible adaptability of life. Each group found its own path to the skies, unlocking new ecological niches and opportunities. This journey mirrors our own evolutionary path, as early humans developed bipedal movement, allowing us to explore and dominate new environments.
Our curiosity about our own evolution led to the creation of the series “Becoming Human,” which explores the defining steps that made us the unique species we are today. By examining our closest living relatives, we gain insights into our place on the evolutionary tree and the traits that set us apart.
Examine the anatomical structures of different flying organisms, such as dragonflies, macaws, and bats. Create detailed sketches or models to highlight the differences and similarities in their wing structures. Discuss how these adaptations suit their environments and lifestyles.
Develop a timeline that traces the evolution of flight from the Devonian period to the present. Include key milestones such as the emergence of insect flight, pterosaurs, birds, and bats. Use creative visuals and annotations to illustrate the evolutionary journey.
Engage in a debate about the different hypotheses regarding the evolution of flight, such as the tergal vs. pleural hypotheses for insect wings, and the arboreal leaping vs. ground-up theories for pterosaurs. Formulate arguments based on scientific evidence and present them to your peers.
Analyze fossil records of early flying organisms like Archaeopteryx and Rhyniognatha hirsti. Discuss the significance of these fossils in understanding the evolution of flight and how they contribute to the broader narrative of life’s history on Earth.
Design and conduct an experiment to simulate different flight adaptations. Use materials like paper, fabric, and wire to create models of wings with varying shapes and sizes. Test their flight capabilities and analyze which designs are most effective, drawing parallels to real-world examples.
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 confined to its aquatic environment. Sea sponges, worms, and jellyfish were all locked within their watery domain. Life above the surface seemed inconceivable and impossible for all of Earth’s early creatures—until about 440 million years ago, when the first organisms ventured onto land. Soon, life on terrestrial Earth exploded, with various plants and animals colonizing the globe.
However, even with this expansion, Earth still had a final frontier: the sky. It seems improbable for life to exist in such an environment. How can small and random genetic mutations enable an animal to transition from being land-based to soaring through the skies? If you look out your window today, you’ll see many creatures that have taken to the skies to avoid predators or exploit new sources of prey.
The more closely you examine birds, bats, and insects, the more distinct their methods of flight appear. Compare the wings of a dragonfly to those of a macaw and a flying fox; the differences are immediately apparent. One has scaled wings, another has feathers, and the third has webbing stretched between thin bony fingers. Even more astonishing is the fact that the ancient ancestors of all three were wingless. Given their divergence on the evolutionary tree, we can see that wings evolved separately three times. This adaptation even occurred a fourth time in the now-extinct pterosaurs.
The story of these different evolutionary paths has fascinated scientists for decades. How do such different organisms transition from land to sky? This question’s answers are still unfolding, beginning nearly 400 million years ago in the Devonian period.
The early fossil records of insects are extremely scarce and hotly debated. Among the oldest known fossils is *Rhyniognatha hirsti*, first discovered in Scotland and dating back to around 400 million years ago. It is a fragmented fossil, with only parts of the head preserved well enough for study. Scientists continue to argue over its classification; some suggest it is one of the earliest insects, while others believe it should be classified as a millipede.
Unfortunately, the earliest fossil record for insects is sparse and unclear. There are far more ancestors of arachnids and myriapods in the early record than there are insects. This changed about 325 million years ago when the number of insects seemed to explode—why? Because suddenly, they were flying. The oldest of these flyers resembles an ancient dragonfly. The real mystery is how insects developed wings in the first place. Unlike other flying creatures, insect wings didn’t evolve from existing arms, and it is exceedingly unlikely for organisms to suddenly evolve a whole new body structure. Did the wings instead come from a pre-existing body structure? If so, which one?
This question has been a major mystery in biology for decades. Over time, two main hypotheses emerged: the tergal hypothesis, which suggests wings originated on the insect’s back as membranes for gliding, and the pleural hypothesis, which suggests wings evolved from the side body and began as limbs that gradually migrated to the back. The scientific community has been divided over which of these could be correct for years.
Recently, researchers have made progress not by looking at insects but by examining crustaceans and arthropods. They sought to determine how the seven leg segments of some crustaceans correspond to an insect’s six segments to figure out which segments are homologous. In evolution, homology refers to similar body parts in different animals due to a shared ancestry.
Using a CRISPR technique, researchers found that insect and crustacean legs are homologous if you count the segments from the leg tips toward the body. They also identified wing genes within part of the insect’s tergum, suggesting that insect wings evolved as outgrowths of the tergum. So millions of years ago, the eighth leg segment for some became wings. While this debate isn’t fully settled, we do know that insects evolved flying only once, and it was such a useful adaptation that they have become among the most successful of all animals.
They inhabit every continent and exhibit a stunning array of behaviors and niches. Once insects, an important food source, took to the air, the ability for flight began to evolve elsewhere in the animal kingdom. The next animals to fly were the largest flying creatures to ever exist: pterosaurs.
Pterosaurs were flying reptiles that ranged in size from that of a pigeon to that of a Cessna aircraft. They lived between 225 and 66 million years ago, successfully cruising the skies for around 160 million years—much longer than modern birds have existed. While some were astonishingly large, most early pterosaurs were relatively small and insectivorous.
Several hypotheses exist regarding how pterosaurs developed their wings. The arboreal leaping theory suggests that the earliest ancestors of pterosaurs hopped around tree branches, evolving first to glide and then to fly. The ground-up theory posits that pterosaur ancestors were terrestrial and might have run and jumped to catch prey, eventually developing wings. Recent studies have shown fossilized tracks from early pterosaurs, indicating they were agile quadrupedal walkers.
The fossils we do have show an incredible range of diversity, especially in the second half of their existence. About 125 million years ago, they became even more diverse, possibly due to the arrival of more flying creatures, including ancient birds.
The oldest fossil ancestor of modern birds is *Archaeopteryx*, dating back 150 million years. Discovered in Germany shortly after Darwin published “On the Origin of Species,” its unusual body contributed significantly to the debate about evolution. *Archaeopteryx* had a mix of avian and reptilian features, allowing it to fly while also possessing teeth and a long bony tail.
Modeling suggests that its wing movement was quite different from modern birds, resembling a swimmer’s butterfly stroke rather than the up-and-down motion we see today. Earlier species of dinosaurs also had feathers, suggesting that feathers might have initially been an adaptation related to sexual selection.
If feathers weren’t the primary factor leading to flight, what was? Similar to pterosaurs, the main hypotheses for avian flight include the trees-down and ground-up theories. Tests with winged robots indicated that gliding was more beneficial than flapping while running, suggesting that gliding between trees may have spurred birds to develop flight.
Ultimately, pterosaurs and dinosaurs went extinct after a meteor impact 66 million years ago, but birds continued to thrive in the aftermath, showcasing remarkable adaptations for flight. Like pterosaurs, birds have hollow bones to reduce body weight and unidirectional respiratory systems, allowing for more efficient oxygen intake.
After the meteor extinction event, birds weren’t the only ones to fill the aerial niche; they were soon joined by bats. The oldest known bat fossil dates back to 52.5 million years ago and is known as the quad bat due to having claws on all five fingers. Researchers suggest that this ancient bat climbed trees and may have even been quadrupedal when not flying.
A significant question regarding bats is whether they evolved echolocation or flight first. While researchers have debated the anatomy of ancient bats, no definitive answers have emerged. The most likely pathway to flight for bats appears to be that they started as gliders.
Bats developed unique flight characteristics compared to birds. Their wings, called patagia, are formed by skin membranes stretched between their fingers, allowing for greater flexibility and fine motor control. Bats have as many as 25 actively controlled joints in their forelimbs, enabling them to twist their wings into various shapes, making them extremely agile flyers.
However, bats have a biphasic airflow system, similar to humans, which is less efficient than birds’ unidirectional airflow system. This may explain why there are large flying birds but no enormous bats. The largest bat today is the flying fox, with a wingspan of up to five feet, while the wandering albatross has the largest wingspan of any bird, reaching 11 feet.
Despite their differences, bats have been remarkably successful, with over 1,400 species existing today, accounting for nearly a quarter of all mammal species and found on every continent except Antarctica.
Life on the wing has proven to be advantageous. While bats, birds, insects, and extinct pterosaurs found their way to flight through different evolutionary pathways, they each discovered an entirely new world of possibilities in the sky.
Evolution teaches us that every possible niche on Earth can and will be filled, no matter how unlikely it seems. Interestingly, the journey to flight for these animals mirrors our own evolutionary journey. Just as flight unlocked new niches for many creatures, bipedal movement did the same for our species.
Early upright humans soon dominated the planet, but how did our ancestors evolve such a unique form of locomotion? What about bipedal movement made our species so successful? These questions have intrigued me for years. On this channel, I often discuss the evolution of other animals, but I wanted to explore our own evolution in depth.
This curiosity 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 place on the evolutionary tree. It’s hard to gaze into the eyes of great apes without seeing a reflection of ourselves.
Chimps, gorillas, bonobos, and orangutans all resemble us in many ways, both in body and behavior. But how did we diverge so drastically from other primates? Is it just our large brains that set us apart, or is there something more?
What were the defining steps in our evolutionary history that made us the walking, talking, thinking, feeling society-building apes we are today? What were the moments that made us human? I wanted to take our time with this subject and focus on quality storytelling, which is why “Becoming Human” is our first Nebula original series.
Nebula is the perfect platform for us to experiment with new content. It’s a space for our videos to exist free from the constraints of the YouTube algorithm. Right now, you can watch the first episode of “Becoming Human” on Nebula. It’s a place full of exclusive original content from various creators, and signing up is the best way to support this channel.
You can also check out our previous video about the world’s biggest, stinkiest, and weirdest flower or watch Real Engineering’s latest video about the incredible engineering of the Spitfire.
Evolution – The process by which different kinds of living organisms are thought to have developed and diversified from earlier forms during the history of the earth. – Charles Darwin’s theory of evolution by natural selection explains how species adapt over time to their environments.
Flight – The action or process of flying through the air, a key adaptation in many species for survival and reproduction. – The evolution of flight in birds involved significant changes in their skeletal structure and muscle distribution.
Insects – A class of invertebrates within the arthropod phylum that have a chitinous exoskeleton, a three-part body, and typically three pairs of legs. – Insects are the most diverse group of animals on Earth, with millions of species adapted to nearly every ecosystem.
Pterosaurs – Extinct flying reptiles of the Mesozoic era, characterized by wings formed by a membrane of skin, muscle, and other tissues stretching from the ankles to a dramatically elongated fourth finger. – Pterosaurs were the first vertebrates to achieve powered flight, predating the evolution of birds and bats.
Birds – A group of warm-blooded vertebrates constituting the class Aves, characterized by feathers, toothless beaked jaws, and a high metabolic rate. – The fossil record shows that birds evolved from theropod dinosaurs during the Jurassic period.
Bats – Mammals of the order Chiroptera whose forelimbs form webbed wings, making them the only mammals naturally capable of sustained flight. – Bats have evolved echolocation as a means of navigating and hunting in the dark.
Adaptations – In biology, the process by which a species becomes better suited to its environment through evolutionary changes. – The thick fur of polar bears is an adaptation to the cold Arctic climate.
Fossils – The preserved remains or traces of organisms that lived in the past, often found in sedimentary rock. – Fossils provide crucial evidence for understanding the evolutionary history of life on Earth.
Hypotheses – Proposed explanations for a phenomenon, based on limited evidence as a starting point for further investigation. – Scientists have developed several hypotheses to explain the rapid diversification of life during the Cambrian explosion.
Ecosystems – Communities of living organisms in conjunction with the nonliving components of their environment, interacting as a system. – Coral reefs are complex ecosystems that support a vast diversity of marine life.
