Since the human species originated on Earth a few million years ago, a total of 117 billion humans have lived. Out of those, about 8 billion live today. In other words, about 7% of all the people who ever lived are around today. This is a remarkable fact, given that the typical life expectancy in the Western world today, about 80 years, is 30,000 times shorter than the span of human history. In other words, if we draw a random person from the population of humans who ever lived, that person has a 7% chance of living during the last 0.003% of human history.
The likelihood of an individual to live today is enhanced by the fact that life expectancy before the Middle Ages was only about 30 years. The chance of living when Christ was born is merely 0.26%, because only 600 million people had lived at that time. However, because of their short lifespan, about 55 billion people had lived before Christ, nearly half of the humans who ever lived.
These early humans, half of all humans who ever lived, had no access to the communication facilities offered to us now by the printing press or the internet. As a result, we know very little about their lives. Proto-writing is traced to the Jiahu symbols in China at about 6,000 years before Christ and writings date back to about 3,500 years before Christ in Egypt, Mesopotamia and the Sumerians. We cannot truly appreciate how much our current life has been improved by science, technology and medicine over the past century, because of the lack of documentation on how the first half of humans lived their life.
The increase in population size over human history also implies that the smartest human who ever lived on Earth has a substantial likelihood of being alive among us right now. When Albert Einstein derived Relativity and Quantum Mechanics, there were about 2 billion people alive, a factor of 4 less than today. Given the larger sample of people living today, it is more likely that a genius smarter than Einstein lives today than during Einstein’s time.
However, we should keep in mind that this present-day genius might have been born in poverty, in a country controlled by a dictator or in a remote village with poor sanitary conditions. As a result, the potent brilliance of that human brain might never manifest itself. It is also possible that this person was bullied on social media or did not satisfy the esoteric requirements of academic selection committees and hence never approached a privileged pulpit for public expression of wisdom. Because of lack of documentation, half of the humans who lived before Christ remain unknown to us. Among them, there must have been an Albert Einstein or a Marie Curie who never recorded their insights.
We can calculate the likelihood of having a genius, the most extreme outlier in human intelligence, by considering the rare tail of the human population at any time in human history. Each newborn baby that came out of an independent womb represents a new sample of the cognitive abilities of the human brain. The Central Limit Theorem in statistics states that for a large sample of independent units, the probability distribution converges to a normal (Gaussian) distribution with some mean and standard deviation.
The tail of the distribution is exponentially suppressed, diluting rapidly the likelihood for an individual who is many standard deviations away from the mean of the population. Assuming that the statistical distribution of cognitive abilities follows this normal function, we can use the number of people who lived at any given time to find how many standard deviations was the smartest person away from the mean.
The deviation of the smartest person from the mean cognitive ability is obtained by equating the probability in the tail to one person out of the total number of humans who are alive at any given time.
Based on the growth in the human population over time, I find that the smartest person was 5.2 standard deviations above the mean 50,000 years before Christ, when humans left Africa to populate the world all the way to Australia. Perhaps that wise person had the brilliant idea to engage in this migration. There were only 2 million people at that time.
Today, with 8 billion people around, the smartest person is 6.5 standard deviations above the mean. Even though the change between 5.2 to 6.5 standard deviations above the mean sounds minor, it corresponds to a probability reduction by a factor of 4,000, reflecting the ratio between the size of the populations at these times. In other words, the smartest person today is smarter than the smartest neanderthal by more than 1.3 standard deviations in cognitive abilities, just because of the increased population size, putting aside the benefits from larger brain size, better nutrition, modern medicine and cumulative knowledge from modern science and technology.
How much smarter might extraterrestrials be? If a substantial fraction of the ~100 billion Earth-Sun systems in the Milky-Way galaxy developed a population of ~100 billion human-like brains similarly to present-day Earth, then the smartest brain that our galaxy ever hosted is 9.9 standard deviations away from the mean, 1.5 times farther than any earthling who ever lived. And assuming the same for the trillion of similar galaxies in the observable volume of the Universe, I find that the smartest brain that we might communicate with since the Big Bang is 12.3 standard deviations away from the mean, nearly twice farther than the smartest human on Earth.
This is good news for those of us who enjoy learning from others. If we find the smartest extraterrestrials, we could benefit from their elevated intelligence. The experience would resemble meeting a smarter student in a class. Sure, our ego might be hurt but imitating that student would allow us to do much better than we did so far in human history.
ABOUT THE AUTHOR
Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011–2020). He is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. His new book, titled “Interstellar”, was published in August 2023.
