08 The First Animal
You are a collection of human parts.
The first animal. The one you, me, we, are all descended from, all animals are descended from. It was the choanoflagellate and it swam in our sea 800 million years ago. How we know this and what it means is fascinating.
2.1 billion years ago prokaryotes were floating around our ocean. Single cells with DNA flopping around their insides, no nucleus, but they did have flagellum. That’s a hair like thing that sticks out of the single cell to allow it do whip the water, usually for some kind of mobility. 200 million years later at 1.9 billion years ago, some of these prokaryotes evolved into Cyanobacteria, some didn’t. These Bacteria tend to be small, circular or there abouts, and did things like use sunlight to convert our carbon dioxide heavy atmosphere into an oxygen one. Then 400 million years later something truly remarkable happened, episode 6, well not episode 6 Energy, but as covered in that ep the Eukaryote appeared, that’s 1.5 billion years ago for those who are counting. Bacteria got inside a prokaryote, became symbiotic, then more than that. The Eukaryote is one advanced single cell with massive energy potential (relatively for the time).
700 million years later, the first animal appeared, 800 million years ago. The choanoflagellate. A single cell that has a cone like set of microvilli around its flagellum. Each microvilli is a rod but they are stuck together to make the cone. The flagellum whips the water and circulates nutrients to the microvilli.
In the 700 million years the choanoflagellate took to arrive it would have encountered some stable environments and some changing ones. Specialisation allows energy efficient use of stable environments, and the best way to replicate as a cell is by sell devision, also more broadly known as asexual reproduction. Choanoflagellate can do this. Also, where the environment changes, evolution selects for diversity and then best fitting. The best way to reproduce for diversity is sexual reproduction. Choanoflagellate can do that too! It produces eggs and sperm! Yet remember it’s a single cell animal, so somehow it’s evolved a way to have a specialised cell division. Rather than full cell division, it divides a special chunk of itself off. It can do both!
How the heck do we know all this from the fossil record? Well we don’t. We know this because they are still around. Just because something else evolves, doesn’t mean the original dies out. As long as they still have a niche, they live on. Out there in our world right now some form a community we know as a sponge. Now don’t do it, but you can blend a sponge into a liquid, pour it out and it will just keep going, reforming.
The choanoflagellates in a sponge whip their flagellum around to circulate water over their microvilli. They have evolved to connect together so they can all line up and have a cumulative effect. How they connect together is how our cells link together, and it doesn’t exist anywhere else outside the animal kingdom. In a circular tower they can really improve their flow of nutrients. Also they can improve their sexual reproductive rate if they emit sperm and eggs at the same time throughout the colony. For that coordination and for probably many reasons, they needed to learn to communicate. They did, and the intracellular communication between them is mostly the same as the intracellular communication inside out bodies.
Given that nerve cells are whole cells and these are whole single cells, the can’t communicate electrically, so they communicate chemically. Chemical communication is as old as the animal, as it is part of what makes an animal. When you eat, you physically fill your stomach, and the nerves in body tell you you feel a full thing there, but you don’t feel full until the chemicals arrive in your brain. The linking, chemical communication and the ability to spawn specialist cells, the first being the egg and the sperm, gives us the tools to begin multi-cellular life. You can readily imagine another specialist cell dividing out but being held onto. A separate animal but dependent on the first, which is dependant on it. A self-symbiant, and we to some degree, still operate that way.
You are not single human. You are a collection of human parts. That sounds more morbid than I mean it, but it’s why we can have cognitive dissonance. It’s why for one part of your body to be satisfied, it may not want or need another part of your body to be satisfied. You are a collection of demands with a hierarchy set by strength, and the oldest traits are the strongest, as any old trade that wasn’t has been lost.
Know yourself.
We should respect this first animal and stop calling it it. We can’t call it her, as the cell which produces the egg also produces sperm. Equally, we can’t call it him, as the reverse is true, the same cell that produces the sperm also produces the egg. And to just call it him anyway is just boringly sexist. It is a hermaphrodite. So the correct pronouns for the animal we all come from are, they them.