This week, Donald Trump repeated one of his favorite boasts about himself, one he has made frequently in his presidency. Trump stated that China respects him because of his “very, very large brain.”

I don’t know how large Donald Trump’s brain is. But he is a human, and humans do indeed have large brains, although not the largest in the animal kingdom. It would take six Donald Trump brains, for example, to equal the size of a sperm whale’s.

If we measure brains as a function of body size, however, humans are the brainiest species on Earth, followed closely by dolphins. Most people think of our species, Homo sapiens, as the culmination of a seven-million-year evolutionary journey characterized by a gradual increase in brain size from a chimpanzee-like condition to modern day. The science fiction world often anticipates that brain size will just keep on getting larger and larger hundreds of thousands of years into the future. A quick Google of “future human evolution” reveals images of gigantic-headed humanoids with noggins much larger than our president’s.

But, over the course of the last 30,000 years, human brains have not gotten larger. They have actually gotten smaller.

Humans today have quite the range of variation in brain size. It would take, on average, three pints of beer to fill an empty human skull (less than a pint would fill an average chimpanzee skull). For a few very large-brained individuals, it would take four pints. But, those four-pinters are pretty rare. And, it turns out, pretty meaningless. Studies in humans have found that the relationship between brain size and measures of intelligence—which themselves are deeply flawed—is weak at best, making individual human brain size mean not very much at all. Albert Einstein’s brain, for example, was only a tad larger than two and a half pints. Sorry Donald—a very, very large brain may mean little more than having a very, very large head.

Now, most readers have correctly heard that Neandertals had larger brains than humans do today. Our ice age cousins had a lot more four-pinters. But, what is less appreciated is that Homo sapiens fossils from the very same time period as Neandertals had the same enormous brains—on average about 10 percent larger than humans have today. And, perhaps Trump’s claim that China respects large brains is rooted in some Chinese national pride. The largest fossil skull discovered to date is a four-and-a-half–pinter found in 115,000-year-old sediments in Lingjing, China just last year. Some think it may belong to the mysterious Denisovan population that lived in Asia during the later Pleistocene.

The human fossil record indicates that brains—after remaining roughly chimpanzee-sized for the first half of our lineage’s history—did indeed increase in size over the course of the last three million years. Fascinatingly, a few small-brained species persisted until quite recently: Homo floresiensis (known by many as the Hobbit) in Indonesia and the recently discovered Homo naledi in South Africa. Yet, in general, brains in humans about 100,000 years ago were big. But, starting around 30,000 years ago, they began to systematically decrease in volume. And no one knows why.

Some scientists hypothesize that this decrease was about efficiency. Brains take up only 2 percent of our body weight, but they exhaust 20 percent of our energy. They are quite expensive to run—stealing every fifth inhalation of oxygen and every fifth swallow of food. But, what if they ran more efficiently at a smaller size? Computers used to be the size of rooms and now they fit in our pockets. Maybe brains evolved the same way, taking advantage of small mutations that make neurotransmitters more efficient.

Some scholars have proposed that brain reduction is just a function of body size reduction. Our ice age ancestors were actually larger than pre-industrial humans. Maybe brains just scaled down as humans got a little smaller? That certainly seems to explain some of the change, but scientists who have explored this question have found that the decrease in body size is not nearly drastic enough to explain the brain drain.

One researcher has proposed that our decrease in brain size coincides with the domestication of the dog. Maybe our canine companions became an externalized brain and we could afford to reduce certain parts of our own brain? Others have posited that it is we—the humans—who have become domesticated. It has been demonstrated that less aggressive, domesticated animals, from dogs and cats to cattle and pigs, all decrease brain size compared to their wild ancestors. Maybe we have domesticated ourselves and followed the same trend of brain size reduction?

But I wonder if it is something more, perhaps something to do with how humans interact with each other. Social insects like wasps and ants don’t really have brains, but they have clumps of neurons called ganglia. And these clumps get bigger and bigger in species that have larger and larger populations. It is possible that they have to have more smarts to learn everyone’s name and role in the insect group. But, in species that have exceptionally large populations (think hives), the ganglia are surprisingly smaller. In these insects, individuals fill specific roles: queen, worker or drone.

Maybe that is what happened to humans. I happen to be a college professor, but I don’t know the first thing about combat, cooking or computers. I rely on other humans to learn the skills that keep me safe, fed and informed. Maybe, as some have proposed, we started relying on the knowledge of others a bit more for our own survival 30,000 years ago rather than each individual having to know everything there was to know to survive.

But this trade of our own individual intelligence for a collective intelligence could only work if our ancestors had shared goals and values. Individuals would need to work together, respect one another and value everyone’s contributions to society. I can be an anthropologist because there are cooks, chemists and carpenters. Perhaps our small brain compared to our Pleistocene ancestors is not something to be ashamed of, but rather something to celebrate—it is a physical reminder of our reliance on one another and our shared humanity.

Perhaps then we shouldn’t brag about our large brains, but marvel at the more compact brain we have inherited from ancestors who likely had to work together to survive. Our world faces real problems, and these problems are not going to be solved by one guy with a self-reported large brain. And Trump should consider if he really wants to be included among the large-brained crowd. In 1871, Edward Rulloff’s brain was weighed at Cornell University where it is still on display. Scientists declared it one of the largest ever recorded.

Rulloff was a serial killer.