President Donald Trump and Secretary of State Rex Tillerson during a bilateral meeting. AP Photo/Alex Brandon President Trump has challenged Secretary of State Rex Tillerson to an IQ test following Tillerson's comment allegedly labeling Trump a "moron." Mensa, the prestigious high-IQ society, has even offered to proctor the test.

There is one hiccup in the president's call to action, however: A person's IQ says almost nothing about his or her intelligence.

Science has been trying to measure people's cognitive firepower for hundreds if not thousands of years. In 1909, French psychologist Afred Binet developed the first test meant to measure a person's intelligence quotient, or IQ. It was designed to weed out the bright French schoolboys from the dimmer ones.

More than 100 years later, the "IQ test" has become a generic way of referring to any intelligence test that purports to standardize someone's intellect and reduce it to a single number. But there are multiple IQ tests that each measure different aspects of a person's mental abilities: spatial reasoning, pattern recognition, numeracy, memory, vocabulary, and more.

As IQ has become the de facto benchmark for being smart, scientists have begun studying what, exactly, IQ tests measure. The general consensus: very little.

In 2012, scientists from the University of Western Ontario conducted the largest online study to-date of people's intelligence. The team issued 12 different tests to more than 100,000 people around the world. Each test sought to pick up on a different aspect of people's brainpower, rooting around for a single measure — what the team called "IQ" — to unite the highest scorers.

What the team found, however, was that intelligence was scattered haphazardly among the dozen metrics. Only three measures correlated with one another: memory, reasoning, and vocabulary, which meant there was no single trait that could describe people as having a high or low IQ. Follow-up tests using functional MRI, a tool that exposes blood flow to certain regions of the brain, showed that disparate regions of the brain governed different tasks.

The evidence told researchers that intelligence was multi-faceted in both how it's manifested in the brain and in the real world.

"The results disprove once and for all the idea that a single measure of intelligence, such as IQ, is enough to capture all of the differences in cognitive ability that we see between people," Roger Highfield, the study's lead author and director of external affairs at the Science Museum in London, told the Telegraph.

In other words, the challenge Trump issued would really only capture the two men's ability to perform that specific test. No test could capture the full spectrum of human intelligence, according to the available body of scientific evidence. It could be the case that one person excels in spatial reasoning while the other has a stronger memory, or vice versa.

In either case, no one could generalize the findings to make any legitimate claims about who is "smarter."