Evolution Q&A: Why did only humans become intelligent?

Ahmad Fares has asked me a second question about evolution. Because he was very polite and sincere in our last discussion, I will try once again to give a thoughtful and complete answer this time as well.

Ahmad's tweet.

Just as with the last time we talked, Ahmad, I’d like to start by talking a little bit about the context of your question.

You have said openly and plainly that you do not believe in the  theory of evolution, and that the purpose of your questions is to cast doubt on the theory of evolution. In this particular case, however, I don’t quite see how this question fits into the “grand scheme” of that goal.

Are you trying to imply that if the theory of evolution were true, then it “should” have produced more than one species with our level of intelligence? I’m not sure exactly why you would think that.

For one thing, intelligence is not an all-or-nothing phenomenon. Humans are smarter than chimps, and chimps are smarter than dogs, and dogs are smarter than mice, and mice are smarter than starfish. Humans happen to be an extreme on the scale of intelligence, when compared to other species.

But we are not the only extreme species. Whales are extreme when it comes to size; hummingbirds are extreme when it comes to the speed with which they flap their wings; bacteria are extreme when it comes to being very small; giraffes are extreme when it comes to having long necks; and barnacles are extreme when it comes to the size of their penis (relative to their body size).

In a world where there is such variation in sizes and shapes and types of creatures, it is only natural that there will be different creatures that are at the extremes for different traits. For humans, it happens to be intelligence.

So one way to look at your question is to point out that humans aren’t the only things to become intelligent. We are simply the species that happens to be the most intelligent. We aren’t especially big, and we aren’t especially fast. Intelligence just happens to be “our thing”.

For another thing, the fact that there are species that have unique and distinct traits, different from all of the others, is not at all contradictory to the theory of evolution. There are many random processes, not guided by design or intelligence, that give rise to unique and unusual situations.

You dump a bowl of oranges on to a table. They scatter, and one rolls on to the floor. Do you ask: “Why did only that one orange fall onto the floor? Does that mean that one orange was given a special reason to fall on the floor?” Or did it just happen?

You pour water over your plants. Some falls on the soil, some falls on the leaves, and one drop falls into a flower petal. Can I therefore conclude that you must have intended that one specific drop to fall on the flower petal? That some special force directed that one drop to fall in a place different from the others? Or did it just happen?

Sometimes, when nature is going about its normal, chaotic, random activity, some things happen differently than other things. That’s just part of how nature works.

But maybe  you were implying something else.  Maybe you are suggesting that intelligence seems like a very useful thing, and that it seems intuitive that many things would have also evolved this useful characteristic. For example: wings are useful! And many things evolved wings: insect, birds, some weird kinds of lizards, and so on. Why isn’t it also like that for intelligence?

To answer this, I have to go back to one of the basic principles that I described in my earlier response to you: evolution actually does not have a bias toward evolving things that are particularly useful in a general sense. That is a misconception about how evolution works. Evolution is based on the idea that differences happen randomly, and when a random difference is especially harmful, it is weeded out. This leaves the next generation that is slightly different in its overall average composition than the earlier generation.

To help to illustrate this better, let’s talk about giraffes for a moment.

Natural SelectionGiraffes have a really long neck. I mean: really, really long. Why are they the only things that have necks that are that long?

There was never any directive overall force that decided, “Hey, look! Long necks would be helpful now! Let’s make that happen!” Giraffes didn’t get longer necks because some giraffe said, “Wow, I wish I had a longer neck! That would help!”

Instead, there were giraffes with many different lengths of neck: some short, some tall. When food was scarce, only the ones with the longer necks could reach the highest branches to get more food. Therefore, they survived. The shorter ones did not get as much food, so they died.  As a result, in the next generation, the average neck length of the entire population was slightly longer. This would then be repeated over and over again.

Of course, it doesn’t get repeated indefinitely. Once all of the giraffes in your population, even the ones with the shorter necks, are well-fed and able to get food, there is no longer any pressure for change. As a result, if food is plentiful and can easily be accessed, neck sizes stay the same.

It’s also important to notice that not every animal’s neck size increased. Monkeys didn’t grow long necks, because they could solve the problem a different way: they climb. There was therefore no reason why short-necked monkeys would die off more than long-necked monkeys.  There is no disadvantage to having a short neck, if you are a monkey.

How does this relate to intelligence?

Intelligence evolved in the same way. Gradually, over time, there were certain characteristics that actually were relevant to survival. The environment was set up so that our ancestors who could use signs and symbols, for example, were able to survive and reproduce better than those who couldn’t. So as a result, those traits spread throughout the population.

But different animals live in different environments, and in different niches. A lion is the king of its domain: at the top of the food chain. If one lion has a better memory than another, or can think faster than another, that doesn’t necessarily mean it will be able to survive better or get more food. It is like the short-necked giraffe in a land where food is plentiful and low to the ground: there is no selection that “weeds out” low extremes of the trait. So if there is nothing that weeds out lions with mediocre memories, then there is no reason for the average power of a lion’s memory to grow. If there is nothing that weeds out lions who can’t solve puzzles, then there is no reason for the ability of lions to solve puzzles to improve.

Intelligence will only evolve when there is a specific problem that it solves. It will only evolve when something in the environment is killing off the animals that are on the “low end” of the population.

Now the final prize-winning question, of course, is what was so special about the environment of early humans that made intelligence an adaptive trait?

Here, I will admit something to you: We’re not certain. There are lots of theories out there. In fact, there are entire books dedicated to the topic. But nobody knows for sure, yet. This is a detail of evolutionary theory that is still being worked out.

That’s ok! These things take time.

But the take-home message that I would like to leave you with is this: there is nothing inconsistent or magical with the idea that humans are the only species that evolved intelligence.  Just like there is nothing inconsistent or magical about the fact that giraffes evolved long necks but monkeys didn’t. This kind of variation and individuality is exactly what one would expect from the principles of the theory of evolution.