Their bodies and brains are going to continue to adapt to an ever-changing world. Yours won't. Will your digestive system be able to handle the same food they eat? Will your brain enjoy the same entertainment? Will your non-evolved tongue even be able to speak the languages they speak in the year one million AD? Would an unfrozen caveman be able to do all of that now?

One thing we do know: You won't be getting any lovin'. It turns out that mother nature hates inter-species breeding, and is such a big cockblocker that science had to come up with a name to describe it: Reproductive Isolation. It's the reason there aren't packs of ligers or centaurs roaming around.

Basically, it's nature's complicated "the triangle doesn't go in the square hole" law, with a bunch of subset rules that will kill off your children if you decide to take a hammer to the triangle. Meaning that as that species further evolves, there is no possible chance for you to create a new species closer to your own that you could stand to look at for five minutes.

Of course, that's assuming that you're even safe walking around among the members of this new freak species. Will they treat you like a novelty and cast you in hilarious insurance commercials, like the Geico cavemen? Or will they do to you what current humans would do if they finally caught Sasquatch roaming around through the forests (that is, stick you in a zoo)? Though whatever the freak-species decides to do with you won't be as bad as no sex for the rest of your life. Who knows, maybe someone will decide to make you the donkey in their next show.

And it's probably irrelevant, since your inability to make friends with mortals will go out the window long before then...

Let's say some kid goes rummaging around in your basement, finds that witch's old portrait of you and discovers that you are immortal. Word spreads and suddenly you're famous the world over. Sure, a lot of people might not buy the story at first, but folks have become famous for much less.

Sounds pretty sweet, right? Probably get a reality show out of it. But that's just scratching the surface. You're not just going to be famous; you're going to be a god. You have eternal life, which means you must know the secret to eternal life, which means you will immediately be the center of the world's newest and most popular religion. You'll be like a guy revealing himself to be Jesus, and proving it. Why would anyone continue to worship an invisible deity when they have a god walking around amongst them? Each morning your yard will be packed full of several thousand terminally ill people, or parents with their sick kids, asking you to grant them the same immortality you have.

That, of course, is assuming a government or crime syndicate doesn't get to you first. Literally every powerful and wealthy person on Earth will decide that in your veins pumps the one thing they can't buy: freedom from death. They're not going to stop until they've spent every penny they can spare to see if they can turn your blood and organs into unending life for themselves. Think about the wars that are being fought over oil. The secret to eternal life would be worth far, far more.

So we're not talking about the occasional blood test and urine sample here and there while they let you stay in some five-star facility. It's more like you getting kidnapped and kept in some damp underground shack away from any civilization while they go balls out on your organs E.T.-style.

"Just contact our concierge if you need anything."

Get comfortable, because since nobody will know where you are, they can keep you there for as long as they want.

But let's say you give them the slip, and successfully keep your secret under wraps with a series of new identities. It's going to get awfully hard to keep track of all of them, because...

We're not saying that if you were to be magically granted immortality, you'd eventually get Alzheimer's anyway--we assume that the Elixir of Life you sipped will keep your brain physically young just like the rest of you. We're saying it won't matter.

Imagine if your cell phone number changed every week, and every week you were forced to memorize the new one. It gets exponentially harder because all of those old numbers are still in your memory, clogging up the works. Then imagine someone asked you to instantly recall the number you had five numbers ago.

"Wait! It had a six in it."

That's one reason your memory degrades as you get older. Your brain and its ability to store and recall memories is limited, but the amount of stuff you're asking it to remember keeps piling up over the decades.

That's a problem because your brain relies on not just storing information, but being able to rapidly recall it at a moment's notice. As time goes on, more and more memories pile up, along with names and dates and birthdays and anniversaries. Your brain can keep all that stuff organized for a while (say, the span of most of a normal human lifetime) but it's not like you can go into your brain and just delete files like cleaning up a hard drive. So useless stuff starts accumulating, clogging up the works and slowing everything down, like all those toolbars on your mom's Internet browser.

"Thanks, Yahoo!"

Your immortal life and experiences may be infinite, but your brain's ability to store and recall them is not. It wouldn't be very long before your brain is piled up with junk like one of the houses on Hoarders. Your body will be young, but you'll still be forgetting people's names and telling the same jokes to the same person twice in one day. Though you'll still be perfectly capable of giving a grumpy speech on where you were when the World Trade Center was destroyed and how kids in the future have it so easy.

And, even if you find a way around this, you still have to deal with the fact that...

Every year of your life seems shorter than the previous one since each passing year represents smaller and smaller portions of your life. It's the same reason a gift of a thousand bucks would be huge news to you, but meaningless to Bill Gates.

So when you're 100 years-old, a minute will seem six seconds long compared to a minute when you were 10. If you live for 1,000 years, a 50-year marriage spent with a woman for her entire adult life, will have the same significance to you as the girl you dated for a few years back in college. If you live for 100,000 years, she'd basically be the nameless chick you made out with at a Weezer concert.

"What was her name? Ah..."

Live to be a million, and people will seem to be just exploding in and out of existence around you, like a time lapse video of a mountain slowly eroding over eons while cities and nations appear and disappear around it, unnoticed. Entertainment will become a dull blur, as you see the same trends and ideas emerge, go out of style and then emerge again for a new generation who thinks they're brand new. You'll have the pleasure of seeing vampires go out of style, then become cool again in 2060, then 2150, then 2200, before you just stop going to the movies.

See, this is why Dr. Manhattan turned into such a dick in Watchmen. But it could be worse...

The only hope you might have is that when they build on the newly vacant spot a decade later, they might discover you along with other dead bodies while moving the rubble. But if the city of Savannah is any indication, people find it easier to just build on top of all the corpses instead of moving them somewhere else.

OK, but really what are the odds you'll be caught in an earthquake (or any other disaster of that nature)? Well, if you live forever, the odds are pretty much 100 percent. Unless the world ends before it has a chance to happen. So now instead of getting trapped in a building, you have to worry about being the lone survivor of a nuclear war, or a giant meteor strike, or another Ice Age, or collision with another planet, or the sun dying.

Or a giant [space] dog mistaking the planet for a meatball.

Even if you make it out unscathed, you're now alone. You'll be forced to live out your life slowly going crazy like a less awesome Will Smith without any zombies to shoot. You won't even have the dog.

And that's assuming the Earth stays intact. A comet could come smashing into the planet like the Kool-Aid Man and send you hurtling through infinite space. Best case scenario is you only float through the void for a few decades before you crash on Mars. At that point you're basically passing the time until intelligent life evolves there. You're going to get really good at making sand castles.

Now what?

So enjoy your life while you're alive. But if you run across the Holy Grail, don't drink from it. It's going to end badly.

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