Every living thing needs energy.  But our world is finite.  Energy has to come from somewhere.

Luckily, there’s a lot of potential energy out there in the universe.  For instance, mass can be converted into energy.  Our sun showers us with energy drawn from the cascade of nuclear explosions that transpire in its core. A tiny difference in mass between merging hydrogen atoms and the resultant helium atom allows our sun to shine.

Our sun radiates about 10^26 joules per second (which is 100,000 times more than the combined yearly energy usage from everyone on Earth), but only a fraction of that reaches our planet.  Photons radiate outward from our sun in all directions, so our planet intercepts only a small sliver of the beam.  Everything living here is fueled by those photons.

When living things use the sun’s energy, we create order – a tree converts disordered air into rigid trunk, a mouse converts a pile of seeds into more mouse, a human might convert mud and straw into a house.  As we create order, we give off heat.  Warming the air, we radiate infrared photons.  That’s what night vision goggles are designed to see.  The net effect is that the Earth absorbs high-energy photons that were traveling in a straight beam outward from the sun … and we convert those photons into a larger number of low-energy photons that fly off every which way.

We the living are chaos machines.  We make the universe messier.  Indeed, that’s the only way anything can live.  According to the Second Law of Thermodynamics, the only processes that are sufficiently probable so as to occur are those that make the world more random.

We’re lucky that the universe started out as such a bland, orderly place – otherwise we might not even be able to tell “before” from “later,” let alone extract enough energy to live.

The earliest living things took energy from the sun indirectly – they used heat, and so they were fueled by each photon’s delivery of warmth to the Earth.  (Please allow me this little hedge – although it’s true that the earliest life was fueled only by warmth, that warmth might not have come from the sun.  Even today, some thermophilic bacteria live in deep sea vents and bask in the energy that leaks from our Earth’s molten core.  The earliest life might have lived in similar nooks far from the surface of the Earth.  But early life that resided near the surface of the seas seems more likely. Complicated chemical reactions were necessary to form molecules like RNA.  Nucleic acids were probably first found in shallow, murky pools pulsed with lightning or ultraviolet radiation.)

Over time, life changed.  Organisms create copies of themselves through chemical processes that have imperfect fidelity, after all.  Each copy is slightly different than the original.  Most differences make an organism worse than its forebears, but, sometimes, through sheer chance, an organism might be better at surviving or at creating new copies of itself.

When that happens, the new version will become more common. 

Over many, many generations, this process can make organisms very different from their forebears.  When a genome is copied prior to cell division, sometimes the polymerase will slip up and duplicate a stretch of code.  These duplication events are incredibly important for evolution – usually, the instructions for proteins can’t drift too far because any change might eliminate essential functions for that cell.  If there’s a second copy, though, the duplicate can mutate and eventually gain some new function.

About two billion years ago, some organisms developed a rudimentary form of photosynthesis.  They could turn sunlight into self!  The energy from our sun’s photons was used to combine carbon dioxide and water into sugar. And sugar can be used to store energy, and to build new types of structures.

Photosynthesis also releases oxygen as a biproduct.  From the perspective of the organisms living then, photosynthesis poisoned the entire atmosphere – a sudden rise in our atmosphere’s oxygen concentration caused many species to go extinct.  But we humans never could have come about without all that oxygen.

Perhaps that’s a small consolation, given that major corporations are currently poisoning our atmosphere with carbon dioxide.  Huge numbers of species might go extinct – including, possibly, ourselves – but something else would have a chance to live here after we have passed.

In addition to poisoning the atmosphere, photosynthesis introduced a new form of competition.  Warmth spreads diffusely – on the early Earth, it was often sheer chance whether one organism would have an advantage over any other.  If you can photosynthesize, though, you want to be the highest organism around.  If you’re closer to the sun, you get the first chance to nab incoming photons.

That’s the evolutionary pressure that induced plants to evolve.  Plants combined sugars into rigid structures so that they could grow upwards.  Height helps when your main goal in life is to snatch sunlight.

Nothing can live without curtailing the chances of other living things.  Whenever a plant absorbs a photon, it reduces the energy available for other plants growing below.

Plants created the soil by trapping dirt and dust, and soil lets them store water for later use.  But there is only so much desalinated water.  Roots reach outward: “I drink your milkshake!”, each could exclaim.

For a heterotroph, the brutality of our world is even more clear.  Our kind – including amoebas, fungi, and all animals – can only survive by eating others.  We are carbon recyclers.  Sugar and protein refurbishers.  We take the molecular machines made by photosynthesizing organisms … chop them apart … and use the pieces to create ourselves.

Some heterotrophs are saprophages – eaters of the dead.  But most survive only by destroying the lives of others.

For the earliest heterotrophs, to eat was to kill.  But, why worry?  Why, after all, is life special?  Each photosynthesizing organism was already churning through our universe’s finite quantity of order in its attempt to grow.  They took in material from their environment and rearranged it.  So did the heterotrophs – they ingested and rearranged. Like all living things, they consumed order and excreted chaos.

The heterotrophs were extinguishing life, but life is just a pattern that repeats itself.  A living thing is a metabolic machine that self-copies.  From a thermodynamic perspective, only the energetics of the process distinguish life from a crystal.  Both are patterns that grow, but when a crystal grows, it makes matter more stable than its environment – life makes matter less stable as it’s incorporated into the pattern.

Your ability to read this essay is a legacy of the heterotrophs’ more violent descendants.  The earliest multicellular heterotrophs were filter feeders – they passively consumed whatever came near.

But then, between 500 and 600 million years ago, animals began to hunt and kill.  They would actively seek life to extinguish.  To do this, they needed to think – neurons first arose among these hunters.

Not coincidentally, this is also the time that animals first developed hard shells, sharp spines, armored plates – defenses to stop others from eating them.

The rigid molecules that allow plants to grow tall, like cellulose, are hard to digest.  So the earliest hunters probably began by killing other animals.

With every meal, you join the long legacy of animals that survived only by extinguishing the lives of others.  With every thought, you draw upon the legacy of our forebear’s ruthless hunt.

Even if you’re vegan, your meals kill.  Like us, plants have goals.  It’s a matter of controversy whether they can perceive – perhaps they don’t know that they have goals – but plants will constantly strive to grow, to collect sunlight and water while they can, and many will actively resist being eaten.

But it makes no sense to value the world if you don’t value yourself.  Maybe you feel sad that you can’t photosynthesize … maybe you’d search out a patch of barren, rocky ground so that you’d absorb only photons that would otherwise be “wasted” … but, in this lifetime, you have to eat.  Otherwise you’d die.  And I personally think that any moral philosophy that advocates suicide is untenable.  That’s a major flaw with utilitarianism – rigid devotion to the idea of maximizing happiness for all would suggest that you, as another organism that’s taking up space, constantly killing, and sapping our universe’s limited supply of order, simply shouldn’t be here.

At its illogical extreme, utilitarianism suggests that either you conquer the world (if you’re the best at feeling happy) or kill yourself (if you’re not).

We humans are descended from carnivores.  Our ancestors were able to maintain such large brains only by cooking and eating meat.  Our bodies lack an herbivore’s compliment of enzymes that would allow us to convert grass and leaves into the full compliment of proteins that we need.

And we owe the very existence of our brains to the hunts carried out by even more ancient ancestors.  If they hadn’t killed, we couldn’t think.

Just because we were blessed by a legacy of violence, though, doesn’t mean we have to perpetuate that violence.  We can benefit from past harms and resolve to harm less in the present and future.

Writing was first developed by professional scribes.  Scientific progress was the province of wealthy artisans.  None of the progress of our culture would have been possible if huge numbers of people weren’t oppressed – food that those people grew was taken from them and distributed by kings to a small number of privileged scribes, artisans, philosophers, and layabouts. 

When humans lived as hunters and gatherers, their societies were generally equitable.  People might die young from bacterial infections, dehydration, or starvation, but their lives were probably much better than the lives of the earliest farmers.  After we discovered agriculture, our diets became less varied and our lives less interesting.  Plus, it’s easier to oppress a land-bound farmer than a nomadic hunter.  Stationary people paid tribute to self-appointed kings.

This misery befell the vast majority of our world’s population, and persisted for thousands of years.  But the world we have now couldn’t have come about any other way.  It’s horrific, but, for humans to reach our current technologies, we needed oppression.  Food was taken from those who toiled and given to those who hadn’t. 

Mostly those others created nothing of value … but some of them made writing, and mathematics, and rocket ships.

Although the development of writing required oppression, it’s wrong to oppress people now.  It was wrong then, too … but we can’t go back and fix things.

Although the origin of your brain required violence, I likewise think we ought to minimize the violence we enact today.  We can’t help all the animals who were hurt in the long journey that made our world the place it is now.  And we can’t stop killing – there’s no other way for heterotrophs like us to live.

To be vegan, though, is to reckon with those costs.  To feel a sense of wonder at all the world pays for us to be here.  And, in gratitude, to refrain from asking that it pay more than we need.