Why Trees Are Taller Than They Need To Be

Have you ever noticed how badly people behave when they are collecting their luggage at the airport? I mean, they all cluster right up against the carousel so people behind them can’t see their bags. And then when you do spot your bag, you have to push through all the other passengers to collect it and usually bump into them as you are grabbing your bag off the carousel. Why is it that people behave so badly? It doesn’t seem to matter which airport you go to anywhere in the world. The problem is the same.

And this problem, believe it or not, is related to why trees are tall. Go with me on this. So why are trees this tall? I mean, some of them are over 115 meters. They are the largest organisms on the planet. And you might think that they are this tall so that they can capture sunlight. And to a degree, that is true. But anyone who has ever walked through a mature forest knows that the lower part of a tree has basically no branches and leaves. And that makes sense, because not enough light filters down through the topmost branches to make it worth having sun-capturing apparatus down here.

Over millennia, trees have evolved to put their energy where it yields returns, that is, in the canopy and not where it doesn’t. But this then begs the question: Why put all this energy into building a trunk that is 10 or 20 meters if you are never intending to use this vertical space to capture sunlight? I mean, it costs energy to make this trunk. Plus, it makes it harder to transport water from the roots up to the topmost branches, and it makes the tree more susceptible to water stress. So it is in every individual tree’s best interest to be shorter, to not have this gigantic trunk and to use the conserved energy to improve its seeds and its branches, to put its energy where it pays a return.

But, of course, if there was a mutation that allowed a tree to do this, you know what would happen to it. In a forest surrounded by all these taller trees, it would be shaded from the sun and so it would wither and die. But what if all of the trees developed the same mutation? What if they all created a friendship pact, a forest of friendship in which everyone agreed not to grow such a big trunk, to start the leaves right at the ground? Well, that would mean every individual tree would be better off.

The trouble is this solution is not stable, because any tiny mutation that results in a tree that is slightly taller would advantage that tree. It would be able to capture more light and it would shade its neighbors. And so pretty soon it would have more offspring. It would come to dominate the forest. And then any additional mutation down the line would result in even taller trees. This is how trees got so tall. I mean, they would keep getting taller until the cost of going one more foot is exactly equal to benefits of collecting that additional sunlight. And that is why trees are as tall as they are today.

I mean, it is not an optimal solution. It is not like these trees have the best use of their energy. But it is the one that is stable. So the point is: Although it is in every tree’s best interest to be a part of this forest of friendship, it will never work. It will never last, because any individual who gets a little bit taller is going to ruin it for everyone.

And it is the very same thing when you go to collect your bags. I mean, if everyone could agree to stand a couple of meters away from the carousel, everyone would have a good view of their bags and be able to easily step forward and collect their luggage. But, of course, one person standing forward is going to block the view of behind them. So everyone is going to rush forward. It is an unstable solution, just like a forest of friendship.

So remember, next time you are frustrated collecting your bags at the airport, remember: Trees know just how you feel.

I have summarized the whole problem for you here. Are you ready?