There’s a question that has plagued both philosophers and evolutionary biologists alike for years: are we, as a species, getting more intelligent with each passing generation, or have our cognitive abilities already peaked, leaving us to a slow, steady decline? According to a new study, you might be right to think the latter.

Gerald Crabtree, a professor of developmental biology at Stanford University in California, recently explained his beliefs in a study published in Trends in Genetics, postulating that any of our ancient ancestors would easily best us intellectually if transported to our time. ”I would wager that if an average citizen from Athens of 1000 BC were to appear suddenly among us, he or she would be among the brightest and most intellectually alive of our colleagues and companions, with a good memory, a broad range of ideas, and a clear-sighted view of important issues,” he said.

The reason as to why is simply due to the fact that human intelligence developed as our best defense to a dangerous world, in which stupidity more often than not lead to death. Since our civilized world includes far less dire threats than our ancestors, who, according to Crabtree, had their intelligence ”honed  in a world where every individual was exposed to nature’s raw selective mechanisms on a daily basis.” The result is that people who would’ve died in those times as a result of stupidity instead find themselves alive today.

“A hunter-gatherer who did not correctly conceive a solution to providing food or shelter probably died, along with his or her progeny, whereas a modern Wall Street executive that made a similar conceptual mistake would receive a substantial bonus and be a more attractive mate,” said Crabtree. “Clearly extreme selection is a thing of the past.” 

According to Crabtree, who admits that his theory is currently untested, it is because of this that genetic mutations may have slowly eroded average human intelligence over the last  few thousand years, explaining that when examining the 2,000 to 5,000 genes responsible for determing a person’s level of intelligence, each of us carries one or two mutations that arose in the last 3,000 that could have lead to future generations steadily becoming dumber over time. 

“We, as a species, are surprisingly intellectually fragile and perhaps reached a peak 2,000 to 6,000 years ago,” Crabtree writes. “If selection is only slightly relaxed, one would still conclude that nearly all of us are compromised compared to our ancient ancestors of 3,000 to 6,000 years ago.” 

Crabtree goes on to suggest that the effects of these slow mutations are already operating in force today, and that we as a species are already deep in an intellectual rut, stating that “one does not need to imagine a day when we could no longer comprehend the problem, or counteract the slow decay in the genes underlying our intellectual fitness, or have visions of the world population docilely watching reruns on televisions they can no longer build.”

Crabtree is not without his detractors, however, who believe that the professor’s bleak diagnosis could be overly pessimistic. Professor Robin Dunbar, an anthropologist at Oxford University, has raised some doubts to the measure of intelligence used by Crabtree, and that the evolutionary process is too slow for such a detrimental change to occur in such a short amount of time.

“[Professor Crabtree] takes the line that our intelligence is designed to allow us to build houses and throw spears straighter at pigs in the bush, but that is not the real driver of brain size,” said Dunbar. ”In reality what has driven human and primate brain evolution is the complexity of our social world [and] that complex world is not going to go away. Doing things like deciding who to have as a mate or how best to rear your children will be with us forever. 

“Personally I am not sure that in the forseeable future there is any reason to be panicking at all, the rate of evolution with things like this takes tens of thousands of years…no doubt the ingenuity of science will find solutions to these things if we do not blow ourselves up first.”

As it currently stands, this debate will remain theoretical until we are capable of conducting proper tests to gauge our levels of intelligence against that of our ancestors. While such a comparison is impossible for now, only time will validate Professor Crabtree’s belief that we are reducing our overall potential for intelligence by existing in a safe, nurturing world. Nevertheless, even Professor Crabtree believes that if his theory is correct, civilization does still have some redeeming qualities that may make up for our theoretical decline in intelligence.

“Remarkably it seems that although our genomes are fragile, our society is robust almost entirely by virtue of education, which allow strengths to be rapidly distributed to all members.”