Why the Gazelle Doesn't Live Forever

A Just-So Story of Co-evolution

Once there was a race of gazelles that were all above average. In fact, they had attained the pinnacle of Darwinian fitness, and were just as strong and as fast as the laws of physics would allow. And every one of them was at this peak, all proud and fit Survivors in the race that goes to the swift.

Of course, they were immortal. Not only were they uniformly in top form, but they could stay that way indefinitely. They never got old, and they never lost their speed.

But just because they were immortal doesn't mean they would live forever. Every once in a while, some freak accident would happen. One would trip and fall, or one was in the wrong place at the wrong time, or there was a terrible storm or a drought...

Still, they lived a long time, because their death rate was uniformly low. So their birth rate didn't have to be very high, and they could have gone on forever, this race of immortal gazelles, graceful denizens of the Serengeti, except...

Except that they shared the plain with a pride of lions. The lions were the very reason that the gazelles had evolved to be so fast. Every one of them could outrun the lions, except...

Except that the very young gazelles were small and new and shaky on their feet, and slower than their perfectly-fit mothers and fathers. The lions could catch the babies, and they did.

So this race of immortal gazelles had no children. They went on living forever, almost, but whenever one of them died, by chance, it was a devastating tragedy, because there was no one to replace him. The herd got a little smaller each year.

The population dwindled. Rumors flew. Elsewhere, there were other herds of immortal gazelles in even worse straits. Many had already been lost. Extinct. They couldn't get their babies to grow up. The situation was desperate.

An assembly was convened of the wisest elders. Luckily, there was no shortage of wise elders. They were perfect, every one; but they were stuck and they knew it. They had to stop the lions from eating their children. But how?

The eldest and wisest of the group put forward his idea. There was no help for the situation without the cooperation of the lions. They must meet with the lions and ask the lions to stop eating their children. But what could they offer the lions in return?

There's only one thing that lions understand, and that's red meat. We have to offer them more meat than they had before.

But where is this meat going to come from. The old, wise gazelles all looked around the room and they knew the answer. To save their children, they would sacrifice themselves.

The gazelles made a pact. They would still be the fastest and the fittest, the most graceful denizens of the Serengeti, but only for a time. Each gazelle would have his chance to grow up, to live, to have children and raise them up. But at the end of the day, they would give themselves up, turn themselves in to the lions for meat.

What we'll offer the lions is ourselves. We'll have more children. There will be more of us growing up, and more of us on the Serengeti. And we'll allow the lions to eat us, every one, not when we are small and scrawny, but when we are fully grown and have five times as much meat to offer.

And here's how we'll do it. We'll give up our immortality. We'll loosen our hold on perfection, and we'll suffer aging over time. We'll get slower after we've been around for awhile, after we've enjoyed our lives and had our children.

There will always be meat for the lions. Plenty of meat. Much more meat than before. As we get old, we'll slow down and we'll sacrifice ourselves to the lions, every one. But we'll do it on one condition: the lions must stop eating our children. They'll continue to take the slowest of us, but the slowest won't be the youngest. The slowest will be the oldest.

They took their pact to the lion king, and the lion king licked his lips, and he signed eagerly on the dotted line. The lions would curb their appetite for speed, while indulging their appetite for red meat. They'd have more to eat than ever before.

And so it was that the gazelles agreed, one and all, to give up their immortality. Each one of them voluntarily grew old and slowed down, until he gave himself to the lions for a meal. And the lions kept to their bargain. They held back their speed, and never again did the lions eat the children of the gazelles, but always preyed on the oldest ones.

The Serengeti blossomed with more lions and more gazelles than it had ever known, and they all lived together in bliss and concord, and demographic homeostasis.