Lesson 7) On the Origin of Species
Professor Gagarina enters the classroom levitating a small aquarium filled with several tangled plants. She is followed by two Fourth Year Hufflepuff students who are each wearing dragon hide gloves; one carries a flaming brazier with sparks leaping from it while the other has a large bowl filled with ice. All items are placed upon the professor’s desk as she turns to face the class.
Welcome, today is the final installment in the story of our planet. That is not to say that the story is finished, but the next chapter is yet to be written by both the universe and yourselves. Here is where it all comes together: it is the story of us.
Earth almost four billion years ago looked very little like the Earth we know today. Continents, created by roiling volcanic activity in the mantle, rose above the waves only to be torn apart by volcanos. Around them liquid water sloshed, covering most of the planet and steaming where the crust split apart. The air was a noxious mix of nitrogen, sulfur, and carbon dioxide. Large celestial objects were still falling from the sky. The land and sea were completely devoid of life.
Let us imagine we can take a Time-Turner all the way back to this time; we would need a Bubble Head Charm to protect us from the harsh conditions on the new Earth. We find ourselves on the edge of a huge continent. A younger Sun shines down upon us; it is much warmer, too, as the gases in the atmosphere here trap far more heat than today’s atmosphere. Behind us a volcano oozes lava down its sides, ash, and hot gases billow from the top. Clouds of sulfurous steam obscure the nearby coastline where the lava meets the ocean. The rocks beneath our feet are scorched and barren: heat, solar radiation, and meteor impacts have made it impossible for life to take hold here.
This strange world is also a land of pure and wild magic. Stone is able to absorb a great deal of magic, but it cannot transform this energy into light or heat. The quantity of magical energy radiating from the Sun and being released by volcanic activity was unable to be absorbed by the metals and rock that made up the Earth’s surface, as a result there was a great deal of magical energy surrounding everything. Performing even the most basic spell in this environment would result in a massive backfire. Keep your wands safely tucked away here; there is too much power to be controlled by any witch or wizard.
The ocean is entirely different. Here, magic is less prevalent as its surface tension acts as an insulator for magical energy and provides protection from light and solar radiation, so this is where many different complex molecules have formed. Instead of clear, turquoise waters this ocean is a primordial soup, filled with all the building blocks of life. It’s getting a bit uncomfortable on land so let’s all dive in and take a closer look: I have a feeling something big is about to happen!
The light from the Sun isn’t so harsh down here and it’s cooler too. You almost feel alone down here. Almost. It happens in a moment, in half an instant; suddenly you’re not alone anymore. It starts with one cell, one tiny organism; but it will be joined by many others. This particular single-celled organism does not possess or interact with magical energy: it is the first mundane life on Earth. That underwater vent over there, however, is spewing more than just heat, gas, and ash into the water. In the water around that vent, there is magical energy in excess. The cells coming together here are not only adapted to magical energy, they have some themselves: they are the first magical life on Earth.
The first life on Earth came to be because of a specific set of circumstances: complex molecules could only exist where they were protected from the damaging effects of heat, light, and radiation. The magical energy on Earth was also a destructive force at that time. Again looking at the Kaybatti River in Turkey, no life is present in the water because of the powerful magical energy the waters contain. While many types of bacteria do grow around volcanic vents, none of these are magical; these bacteria have actually developed a resistance to the magical energy of the Earth. Magizoologists and magibiologists are still studying these super-mundane bacteria to see what effect they have on the ecosystem.
Humans: A History
The very first life on Earth was supremely simple. Amino acids in the sea water came together to create an organism called cyanobacteria. These blue-green algae were also the first producers of oxygen. These and their various relatives would eventually transform Earth’s atmosphere into the oxygen rich environment we know today. It would, however, take a further billion years before the organisms of Earth could begin to use oxygen to breathe.
Approximately one and a half billion years ago, single celled organisms on Earth underwent another significant change. They developed more complex cellular organs including a nucleus, a cell’s “brain,” and the common feature of all plant, animal, and fungus cells. At this time all life reproduced asexually. This meant that a single cell would produce a copy itself instead of combining its genetic material with another’s. This allowed the organisms to flourish, though it offered little genetic diversity. This meant that these organisms were unable to adapt as easily to changing environments and, consequently, they stayed in the water instead of expanding their habitats outside of the ocean. A further five hundred million years would elapse before the first sexual reproduction would occur, allowing organisms to adapt more easily to foreign environments.
It is around this time that life becomes more complex. Instead of single-celled organisms, plants and animals begin to form from collections of cells. Plants are able to grow and adapt more easily as more cells allowed the plants to produce more food and energy from sunlight.
Life on Earth has always moved forward, but that does not mean that the journey has been an easy one. Several mass extinction events have changed the face of life on Earth. The first mass extinction occurred in the Cryogenian Period and killed approximately 70% of all marine plants when the Earth and oceans cooled below survivable levels for these early plants. Despite this disaster, we see that life continued to develop with the first soft-bodied organisms, such as jellyfish, and shelled invertebrates appearing in our oceans.
The Paleozoic Era saw life flourish all over our planet. Marine invertebrates were joined by the first vertebrates while small green plants and fungi made the transition from ocean to land. This achievement was dampened somewhat by a mass extinction in the Ordovician Period when cooling oceans killed many marine invertebrates. Nonetheless fish developed jaws in this period too and these became the first sharks, beginning their 450 million year reign in the world’s oceans. Spiders and centipedes also made their way onto land during this Era, though this is fortunately overshadowed by the appearance of Tiktaalik, the first vertebrate with legs who also made it onto land along with other amphibian species.
Many varied plant and animal species made their homes on land, even as more diverse life came to being in the oceans. This great progress was almost derailed completely during the Permian-Triassic mass extinction. A massive meteor struck the Earth around this time and the resulting climatological changes killed almost 90% of all marine life and 70% of life on land.
This mass extinction paved the way for lizards, birds, and even small mammals. Two and a half billion years after the first life appeared on Earth, life finally took to the skies when the first flying dinosaurs appeared. It was at this point that vertebrates, the overarching family to which all humans belonged, had completely conquered sea, land, and air. However, it will be a further two hundred and fifty million years before a single species comes close to doing the same. Much later we see the arrival of life that looks far more similar to the life we know today. Plants began producing flowers and fruit while birds’ beaks lost their teeth. Crocodiles, another ancient creature, first appeared about one hundred million years ago and, like sharks, have continued to thrive up until today.
The final mass extinction occurred at the end of the Cretaceous Period with the meteor impact at Chicxulub, Mexico which resulted in the end of the dinosaurs. In fact, 80-90% of all marine species and 80% of all land species died in the event. This mass extinction paved the way for birds to begin evolving into today’s species. This time also heralded the beginning of the reign of mammals.
It was not until about six million years ago that the first upright hominids appeared. These ancestors of ours were the result of the unmatched survival of many different species throughout the eons. At each step these species had to overcome predators and natural disasters, changing climates and ecosystems, all to become something that vaguely resembled us. It was only within the last million years that hominids mastered fire, speech, magic, and the environments in which they lived and it has been only about one and a half thousand years since our species appeared on Earth. Today we are the most dominant species on the planet, but we hold in our DNA the history of every plant and animal on Earth. We all came from a handful of cells in a barren ocean to become what we are today.
Most geologists believe there have been a series of supercontinents, massive land structures, culminating in Pangea, a supercontinent that broke apart to become the continents we know today. The evidence for the existence of the supercontinent Pangea is also the story of how it broke apart. When Pangea began to split into the continents we know today, dinosaurs ruled the Earth. Massive forests were filled with similarly massive creatures. As these animals died from predators and natural causes, their bones were slowly replaced by minerals creating the fossils we see in museums and private collections today. The distribution of these fossils and petrified trees, trees that have undergone a similar process of fossilization, shows us where these animals lived on Pangea. Since these distributions overlap across modern continents we can show what Pangea once looked like.
Continents move very slowly, usually only a couple centimeters a year. This means that the climate changed very slowly for continents that moved towards the poles. Creatures on these land masses had time to change and adapt to their surroundings. We could very well still have Tyrannosaurus rex-type creatures roaming the world today if it had not been for the Chicxulub meteor impact.
The impact was so massive that it triggered tsunamis, volcanic eruptions, and earthquakes; dust and ash filled the sky, blocking sunlight and raising global temperatures. Unlike the slow moving change of continental drift, these changes happened too quickly for the dinosaurs to adapt. Over eighty percent of all life on Earth was extinguished 65 million years ago. Dinosaurs that needed a great deal of energy and sunlight to thrive were unable to cope with the harsh conditions; mammals, on the other hand, saw this as their chance to thrive.
Mammals at this time were very small, the size of small rodents today. They were able to adapt to the harsh new climate, however, because they were warm blooded and had fur which made them less reliant on the sun for energy. Their small size meant that they didn’t need to consume as much food, helpful when resources were scarce. It would take another sixty five million years, however, before these mammals had evolved into the many species of mammals we see today.
The Family Tree
All life on Earth began with the single celled organisms that appeared relatively soon after the Earth had formed. How, then, did we end up with the many different species of plants and animals that exist today? The answer is evolution.
Evolution is the process by which living things gradually change and adapt to the world in which they live. While we can see the big changes between species over a very long period of time when we compare, say, a wooly mammoth to an elephant, the changes are very difficult to see from one year or even one decade to the next.
Evolution occurs most often in reproduction. In sexual reproduction, DNA, the chemical code that determines all features of an organism, is combined from two different organisms of the same species. The male and female organism each gives their offspring half of their DNA which combines to form a whole DNA blueprint for the new organism being created. Sometimes the two halves don’t come together perfectly which results in tiny changes to the offspring. If these changes allow the new organism to grow and thrive better than its parents, the new organism has a better chance of surviving to pass these traits on to the next generation.
Changes to DNA don’t just enhance the organism, they also change it. Eventually two creatures of the same species with different DNA changes can become two entirely different species, though this takes a very long time. Sometimes nature chooses which genes, specific parts of DNA, survive, and sometimes humans get to choose.
The process by which nature chooses is called natural selection. When changes to DNA are helpful, that change is more likely to be passed on. The brazier to my right contains magical fire dwelling salamanders, while the bowl to my left contains ice dwelling salamanders. Both species are amphibians. Their mundane amphibian cousins are notable because their skin must always be in contact with water, these two magical varieties require fire and ice, respectively, and depriving them of either will hurt them.
Amphibians are some of the oldest types of animals in the world; they were some of the first creatures to leave the water and move to land. Fire-dwelling salamanders are also very old, magical descendants of the first land animals. Electrical storms and volcanic activity created the first fires that these creatures adapted to live in. As naturally occurring forest fires are still very common, these species have had to change very little over time. Like sharks, whose ancestors are very similar to the sharks we see today, fire-dwelling salamanders are also living fossils.
When Pangea began to break apart, certain magical species found their habitats moving from tropical zones to more temperate climates. Those that could adapt more quickly to cooler temperatures lived to produce more offspring who also had a liking for the cold. Over 65 million years later, we now have magical salamanders who survive in ice. While they are also considered living fossils, this ice-loving branch of the salamander family tree is much newer in evolutionary terms.
While salamanders are small enough to bring into the classroom the same can be said about the various species of dragons. While they share a common ancestor, a gigantic, magical, winged reptile whose power was strong enough to survive the various extinctions; dragons today are all very different. Some have venom while others use different temperatures of flame to hunt and defend themselves.
Natural selection can work fairly quickly to help plants and animals to adapt to more rapidly changing conditions. The early seas of Earth were fairly warm, owing to the greenhouse gases in Earth’s second atmosphere. When photosynthesis took off, a large amount of oxygen was generated. Plants that lived on carbon dioxide were poisoned by oxygen, but a magical plant species began to store oxygen instead of releasing it and even used oxygen to power photosynthesis when there was no sunlight. Today we see several descendants of this magical species. They are the “gilly” family which contains Gillywood trees and gillyweed, these plants in the aquarium you’ll recognize from Year One Herbology, survive through photosynthesis powered either by the sun or by stored oxygen. Its magical properties also mean that when the plant is consumed, it allows you to live and move underwater for a period of time.
Evolution takes a very long time, but it will never stop improving the living things on our planet. As the seasons change, the continents shift, and the years pass our Earth’s story grows ever longer written in the land, the air, the water, and the flora and fauna change and grow. The next chapter of this story will be written many centuries from now.
That will be all for this week. As usual there will be a short quiz and an essay for you to turn in next week, when we will be discussing the possibility of other earths in the universe.
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