ACT I
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The Earth formed about 4.5 billion years ago. Life began about 3.5 billion years ago. So how did it happen? That’s another big mystery people have wondered about for thousands of years.
Scientists are detectives. They’ve searched for the answer the way any good detective would. They used everything they knew to sketch a big picture of the Earth before life began. Then they narrowed their search down by filling in what could’ve happened within that framework.
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4 billion years ago the Earth was a lot different than it is now. Back then it was a big rock orbiting a star.
The geology was a lot the same. There was water, which could get warm enough to vaporize and cold enough to freeze. There was land and oceans, mountains, hills, rivers, and islands. There were rocks, sand, and mud. There was wind, rain, thunderstorms, earthquakes, and volcanos.
The wind blew sand and dust around. The rain washed it downhill. The rivers carried it toward the oceans. Lightning strikes, volcanos, and light from the sun added energy to it. All that dust and water being mixed around and energy being added to it meant chemical reactions were happening all over the Earth.
Physics and chemistry are the foundation of both geology and biology. The difference between geology and biology is evolution. The chemical reactions in biology evolve and the chemical reactions in geology don’t.
Evolution is the product of replication, variation, and selection. The chemical reactions that make up biology start new chemical reactions that are very similar to themselves but not identical, and then outside factors make some of the chemical reactions stop, but not all of them.
For life to begin, the chemical reactions of biology had to be started by geology. So how could the geology of the Earth start a chemical reaction that could evolve?
ACT II
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What does it mean to say that we’re carbon based life forms?
The molecules that make up our cellular structures are carbon in their cores with other atoms connected to the outsides. Most of your body weight is water, but the structures that hold it all together are mostly carbon. That’s like saying that a water balloon is a balloon full of water, not a balloon made of water.
Carbon atoms can bond to each other in long molecules. That’s why diamonds are so hard to break. It’s also why wood and fossil fuels contain so much energy, because big carbon molecules have so many chemical bonds.
All living things, from viruses and bacteria, to fungus, to plants, to animals, to us, are made of the same chemical elements the rest of the planet is. 99% of your body is made of carbon, hydrogen, oxygen, nitrogen, calcium, and phosphorus. The other 1% is made of sulfur, potassium, sodium, iron, copper, zinc, and 13 other ordinary minerals.
Scientists have a number of hypotheses to explain how life evolved. There’s no way to test any of them, because there’s no way to track down an individual chemical reaction that could’ve happened almost anywhere on Earth around 4 billion years ago. Just like with trying to figure out what happened before the Big Bang, these are what scientists call untestable hypotheses. But we don’t need to prove what happened. There are many ways it could’ve happened, and one way or another it did happen.
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How many times could the geology of the Earth create a chemical reaction that evolved? Did life originate from geology only once, or did it originate more than once?
If it only happened once, chemically all life on Earth would be very similar to each other. If life on Earth today began with more than one chemical reaction, then life today could be divided into at least two distinct groups that functioned differently at the molecular level, meaning, the biochemistry of one couldn’t create the biochemistry of the other.
All the genes in the world are made of different combinations of just four chemical sequences, called adenine, thymine, cytosine, and guanine, also called A, T, C, and G. Those are called nucleobases, which are molecules that join together to form bigger molecules.
The biochemistry of cells produces molecules called amino acids. Those are the building blocks of life. Additional biochemical reactions combine them into protein molecules.
The cell structures of all the living things in the world are made of protein molecules. All of the proteins in the world are made of different combinations of just 20 amino acids. Not all living things use all 20. But there aren’t any living things things that don’t use any of them. And there’s so much overlap among which life forms use which amino acids that there’s no way to divide them into smaller groups and say that animals use 10 of them and plants use the other 10, or anything like that.
That means all life on Earth probably did begin with just one chemical reaction.
ACT III
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Here’s the simplest explanation of what could’ve happened.
We know that there’s a lot of carbon in the world. With the original geology of the world, it would’ve been laying around everywhere. We know there were streams and rivers all over the world. That means they carried whatever chemicals were floating in the water over whatever chemicals were in the mud of the river beds.
We know that the atmosphere mixed all the gaseous elements around, and blew dust around. We know that the sun shone on all of it, adding heat, light, and ultraviolet radiation to the world.
That means that right at the waterline of every stream, river, and lake in the world, all four of those things came together. Wherever there was carbon in the mud of a river bank, there was water carrying other chemicals over it, there was dust and atmospheric chemicals in contact with it, and there was sunlight shining on it all day.
Many types of atoms can form crystals under the right conditions. A crystal is a very highly organized pattern of atoms or molecules. Some crystals, like salt and ice, can grow, because when the right kinds of atoms or molecules come into contact with them, they’re absorbed into the crystalline structure. If a crystal like that breaks in half, both halves have the pattern, which means both of them can grow on their own.
All that was necessary for life to begin on Earth was for one chemical reaction to form a carbon molecule that could do the same basic thing as a salt crystal. That carbon molecule could’ve had other atoms in it too, like hydrogen, oxygen, or nitrogen.
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One proto-gene molecule on the surface of the Earth doesn’t sound like much. But as soon as it broke and turned into two molecules, it doubled the number of proto-genes on Earth.
When they each broke they made four, then eight, 16, 32, 64, 128, 256, 512, 1,024. That’s the power of exponential growth. Ten steps of division of the proto-genes multiplied them by over 1,000. They started out small but they spread faster and faster.
Flowing water stirs a lot of chemical reactions around. It was probably involved in the chemical reaction that created the first proto-gene. Even if it wasn’t, it would’ve picked up some of those molecules sooner or later and carried them into a stream.
From there they flowed into the ocean. Eventually that would spread them over 70% of the Earth’s surface, and bring them to the coastlines of every land mass in the world. That gave them a lot of space to replicate.
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Crystals don’t always form perfectly. Sometimes they get flaws. Flaws in crystals are caused by them either absorbing some other atom, or absorbing a regular atom that gets misaligned from the regular structure. But small flaws don’t disrupt the crystalline pattern, so they grow around the flaw and keep growing.
A flaw like that in a proto-gene could make it add a new atom, like hydrogen, oxygen, or nitrogen, and could make it start new chemical reactions. Then if a large proto-gene that had a flaw at one end broke in half, it would create two different genes:
one the original proto-gene, which would cause the original chemical reactions, and the other the flawed proto-gene, which would cause new chemical reactions.
There’s a lot of carbon in the world. That original proto-gene could’ve made its original chemical reaction happen for a long time. During that time a lot of flaws, or as they’ve called in biology, variations, would’ve happened.
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Eventually that original chemical reaction would’ve used up all the carbon that was in a form it could react with. But by then variations had created new proto-genes that could make new chemical reactions happen. That let them use carbon atoms the original proto-genes couldn’t use.
For instance, graphite is carbon. There could’ve been a lot of pure carbon laying around. There also would’ve been carbon that was tied up in chemical bonds with other atoms, like carbon dioxide or methane. If new proto-genes could react with other chemicals in ways that broke them down and released their carbon, they could use that carbon.
Eventually variations in proto-genes created some that could take carbon out of other proto-genes. So those proto-genes started making more of themselves by destroying other proto-genes. Those were the world’s first predators.
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That made another variation valuable. If a proto-gene could surround itself in atoms arranged in forms that other proto-genes couldn’t break down, that proto-gene was protected. In modern biology that’s what a cell wall is.
If two proto-genes stuck together and they each made chemical reactions happen that made it easier for the other to replicate, the two of them together would be better at making copies of themselves than either of them would be alone. That meant they each created more of themselves and those new proto-genes could keep pairing up. So that process continued.
That was the beginning of symbiotic relationships. Two genes sticking together to form a larger molecule was the world’s first chromosome.
Eventually, a cell divided in two, but the two new cells didn’t separate. They stuck together. That was the world’s first multi-cellular life form.
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Now that different types of proto-genes are all using carbon atoms to replicate themselves, they run into Finite = Finite. They can’t all keep making copies of themselves forever. Since there are limits now on how many copies of themselves they can make, how they make copies of themselves is going to start to affect if they make copies of themselves.
The obvious one is productivity. The simpler the process is, and the more common the chemicals a gene needs are, the more copies of itself it will make.
Another factor is longevity. The longer the lifespan of the gene, the longer it can replicate. The fewer things there are that can destroy the gene, the longer it has to make copies of itself.
There’s also the resolution of the copies. When a gene makes a copy of itself, that means the copy can also make copies. If a gene creates a molecule that’s very similar to itself but can’t make copies of itself, that doesn’t lead to any more generations of descendants.
Genes that make more copies of themselves faster than they’re destroyed keep increasing their numbers.
If a type of gene gets destroyed faster than it makes copies of itself, its numbers decline. If that continues long enough, sooner or later all the genes break up and don’t leave any copies of themselves. Then that gene is extinct.
ACT IV
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Molecular biology is hard for many people to understand. Because there are so many millions of chemical reactions involved there’s no way for anyone to memorize them all.
It’s easy for people to feel that anything they can’t understand might as well not be real. If you can’t understand something there’s no way to use it in your decision making. That’s why learning new things depends on finding effective ways to organize information in your mind.
That’s what first principles are for within individual branches of science. They’re the unifying themes that let us tell stories about what happens in that branch of science.
The most important scientific discoveries are the discoveries of first principles that connect branches of science. They let us tell stories like this, where one branch leads seamlessly into another branch. That’s why we can tell one big story of Being Human on Planet Earth now, instead of just telling one story about chemistry and another story about biology.
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Charles Darwin discovered the Theory of Evolution bystudying plants and animals, and discovering how the replication, variation, and selection of their characteristics made their species evolve. That’s what The Origin of Species is about.
Richard Dawkins discovered the Selfish Gene Theory in the 1970s. That shows how the Theory of Evolution plays out at the molecular level. His book about that is called The Selfish Gene.
ACT V
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Many people are convinced that there’s more to life than chemistry. What about love and beauty and music and art? But that’s what happens when nobody figures out how to make biochemistry part of the story of life people grow up with.
It’s true that there’s more to life than what you learn about in chemistry class. But the brain you’ve been using all this time to think about life and paint sunsets and sing songs and fall in love has always been made of carbon,hydrogen, oxygen, nitrogen, and 21 other chemical elements.
If you want to see molecular biology play out in everyday life, try this:
Go anywhere in the world and ask the people you meet there what they think about life. Anywhere you go, people will tell you different words that mean the same thing:
The purpose of life is to keep on living.
Some people interpret that directly and believe in an afterlife. Some people think of that in terms of having children, or extended families. Some people think of it in terms of doing things they value in life that will live on after them. Some people think of it in the short term, as making lives for themselves that they’re happy with.
Even depressed people feel their lives are supposed to be moving toward something good, but either they can’t figure out what it is, or can’t figure out how to get there.
The genes that make life happen are molecules that make copies of themselves. Molecules can’t think because they don’t have brains. Genes make copies of themselves for the same reason rocks warm up when the sun shines on them: Because that’s the end result of the physical process that happens when they interact with a certain combination of environmental factors.
All of our bodies and our organs, including our brains, have been created by our genes as part of the very long and complicated chemical reaction of them making copies of themselves. In other words, evolution.
That means the underlying theme of that chemical reaction is so fundamental to who we are and what we think about that all over the world people think about life, write philosophy books, and believe in religions, and all their central themes turn out to be different interpretations of the underlying theme of molecular biology:
The purpose of life is to keep on living.
No matter how much people wrap their ideas about the meaning of life together with stories about morality, inspiration, the afterlife, and the origin of the universe, the central theme to all of our thinking is only a slightly more complicated version of the central theme of the molecules that create us:
The good ideas are the ones that keep us alive.
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Remember what I’ve said about people always make
the best decisions
they can think of
in the situations
they’re in
for themselves
and the people
and things
they care about?
Now we can see where that starts. The purpose of life is to keep living, and people feel that the best ideas are the ones that keep them alive. We’ve only gotten as far as talking about the molecules we’re made of, and we’re already filling in the picture of why and how and what it means when people always make
the best decisions
they can think of
in the situations
they’re in
for themselves
and the people
and things
they care about.
We’re just getting started. There are still a lot of steps left in between molecular biology and current events.
