It is a biological inevitability that just about every living organism will die—it's the how and the when that are up for debate. Some species barely make it to adulthood, while others go on for centuries. Ninety-nine percent of all species have already gone extinct. In nature, death is everywhere.
One might ask why this is so. After all, the ability to survive seems on the surface to be a pretty desirable trait to evolve. If something is around longer, wouldn't that give it more chances to reproduce? Could a species evolve to live longer and longer—until, eventually, it can live forever? On an even more fundamental level, how well defined are our basic notions of life and death to begin with?
Jules Howard—a zoologist, writer, and broadcaster based in the UK—tackles some of these questions in his new book, Death on Earth: Adventures in Evolution and Mortality. I reached out to him and we talked about it via Skype.
VICE: For starters, is there a consensus on the definitions of "life" and "death"?
Jules Howard: In the British education system, when we do science at around age fourteen, fifteen, sixteen, we do a module about "what is life?" I don't know if it's the same for you in America, but we were taught the MRS GREN acronym. It stands for Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion, and Nutrition. I kind of went into the book thinking: We can define life. Therefore death is just the bit where life ends.
But it's not as simple as that. Mules aren't able to sexually reproduce. They're sterile. So technically, by some definitions, they're not "alive"—but clearly a mule is as alive as anything else. So it's kind of amorphous. It's a nebulous concept, what life and death is. There's a [former Supreme Court] judge's line about pornography: "I know it when I see it." That's kinda where I ended up, really.
In the book, you use NASA's definition for life as a working solution, where life is anything "capable of going through Darwinian evolution."
Correct, for life.
What about for death?
With death, there was the Victorian "not breathing, goodbye, game over." But after the knowledge of [how] to resuscitate someone who was assumed to be dead [started spreading], suddenly the definition of death has changed. And to a lesser degree, brain death. We now know people can give birth in such a state. So what I thought would be a simple label, was kind of anything but. Death is sort of a spectrum of categories.
What are some examples from the animal kingdom that make it hard to draw the line between life and death?
There's tardigrades. They're these little animals where all the water is pulled out of their body, and they become nothing but a little husk of proteins really. Once water splashes on them, they activate again. In that state, when they're literally just a bag of potential, are they dead? Chemically, they kind of are not dead. So there's all sorts of definitions, and I'm not sure we're all agreed on it. I'm sure our current definitions are going to change with medical advances and things like that.
"Evolutionarily, we die because there's only so much sex one can have." — Jules Howard
Do we know why animals age?
There are two ways to go with that. One is we age because living is so tough. Replicating cells is tough business, and we age because when we metabolize, we build up these reactive oxygen atoms, called free radicals. So the more metabolizing we do, the more we build up these free radicals, the more these nightmare particles bump around in our cells and smash up proteins, and the accumulation of those free radicals, one could say is what aging is. So that's what it looks like.
The other one is this idea of DNA strands being like [shoelaces]. The more replications of DNA you have, the more those shoelaces get worn away at the end because you have a set number of potential replications to your cells before telomeres, [which are like the plastic ends of a shoelace], will go.
Do we know why we die?
For me, evolutionarily, we die because there's only so much sex one can have. In all environments, one of the coolest things about animals is you can almost predict their life span according to how much death there is. Insects are going to get eaten by birds. There's no point in them evolving longevity. There's no point in them evolving a long life. They're gonna die. They just quickly get their sex done, as quick as possible. Boom, bash, bin, bop, they're off.
Whereas other animals, where those chances of dying are [smaller], for birds, for us, you see aging become a thing. You see life start to stretch out.
Are there any actually immortal animals?
The classic is the immortal jellyfish. Normally, jellyfish just die at that point once they've had sex. But this one species starts to reverse age back into larval form. That is the only animal that has hit upon that as a strategy, which is really interesting.
Bodies are built through pathways. Imagine them as a set of instruction manuals. So to have pathways that can reverse themselves is amazing really. As far as other animals, you also have hydras, which are in ponds and puddles the world over. It's like a freshwater jellyfish-like creature. [Their] stem cells also have an infinite capacity for self-renewal. So they're not limited by the number of cell divisions they can do. They can just live and live and live.
What about bigger animals?
Birds, bats, and tortoises all have cellular tricks through which they can tame free radicals and slow aging. That's potentially a rich scene for humans to investigate. My favorite is a mussel—a freshwater shellfish—that produces a larva. The larva swims and grabs along to the gills of a salmon. Once attached, the larva injects a little protein, and that protein causes the salmon to deal with free radicals better. So the salmon ends up living not one or two years, but three years. An extra year without cancer or classic diseases of old age in fish. The parasite extends the life of its host basically through chemicals. Imagine if we could potentially engineer little larvae and sniff it! This is what the future might look like for us.
In your book, your biggest concern for humans being able to expand their longevity is the ability to keep our brain healthy. Why is that?
The atoms in our [bodies] are constantly cycling through, so only a few parts of our body are more than ten years old. One of those is the brain. The cells don't replicate in the same way. So if you want to keep your brain running past one hundred twenty years, it's going to be difficult. Because once you get those cells to replicate, you lose experience. You would lose... yourself, in a way. You lose the thing that is you. Are we going to overcome that? Maybe, but it's tricky.
Some male American songbirds, at the end of the breeding season, the lower parts of the brain basically gets recycled. So the following year they have to relearn their songs. If you replace your brain cells, it might help you last longer, but you're going to have to relearn some things along the way.
As part of your research for the book, you went to an anti-aging convention. What impression did it leave with you?
The message I've come away with after writing this book is that actually the idea of living longer is actually an emergent property of not making enough of the life we have. The key message that I've come away with is that this is the bit where we're alive. We've got to acknowledge that this bit is the fun bit and make more of it. That's my feeling about this growing industry of [trying to achieve] immortality.
Let's say that humans became immortal. Does that mean humans would stop evolving at that point?
For me, nothing evolves without death. Animals evolve very quickly in environments with lots of death. With humans, we've kind of gotten rid of our predators. We've invented medicine. Many of the things that killed us in the past no longer kill us now. I think most evolutionary scientists would say our evolution has slowed. So I'm not sure we're evolving much anyway.
So going back to the original NASA definition: If we stopped evolving, would we still be alive?
Wow, that is a brilliant wrap around. Did you plan that?
As a matter of fact, I did.
Well, there's no doubt about it. I am not undergoing Darwinian evolution anymore. But I am alive. We know life. We know death when we see it. So I'd say we're still alive.
Death on Earth: Adventures in Evolution and Mortalitywill be published on May 10.
Follow Simon Davis on Twitter.