“Why Isn’t the Milky Way Crawling with Intelligent Life?” –The ‘Planet of the Apes’ Hypothesis Revisited

The big question is: “is human-like intelligence a convergent feature of evolution? Should we expect to find extraterrestrials with human-like intelligence?”In the “Great Drake Equation Debate” (an equation created by Frank Drake to estimate the number of civilizations in the Milky Way with whom we might communicate via radio telescopes) most experts assumed that once life got started it would get smarter and smarter until one day, it would hit upon the idea of building a radio telescope. “A stupid things get smarter” model of animal evolution and believed it to be a universal trend. Lineweaver calls this idea the “Planet of the Apes” hypothesis.

In 1960 Frank Drake conducted the first radio search for extraterrestrial intelligence. He is the Director of the SETI (Search for Extra Terrestrial Intelligence) Institute’s Center for the Study of Life in the Universe. SETI work would seem much more promising if there has been an evolutionary trend among terrestrial life forms towards higher intelligence.

On a flight to a conference Lineweaver was attending with Drake, he asked: “Frank, why do you think there are intelligent aliens who have built radio telescopes? What do you think is the strongest evidence for the idea that such human-like intelligence is a convergent feature of evolution?” (The European Southern Observatory complex in Chile shown below)

Drake’s answer went something like this: “The Earth’s fossil record is quite clear in showing that the complexity of the central nervous system – particularly the capabilities of the brain – has steadily increased in the course of evolution. Even the mass extinctions did not set back this steady increase in brain size. It can be argued that extinction events  expedite the development of cognitive abilities, since those creatures with superior brains are better able to save themselves from the sudden change in their environment. Thus smarter creatures are selected, and the growth of intelligence accelerates. We see this effect in all varieties of animals — it is not a fluke that has occurred in some small sub-set of animal life. This picture suggests strongly that, given enough time, a biota can evolve not just one intelligent species, but many. So complex life should occur abundantly.”

(Recently the philosopher Peter Godfrey-Smith wrote that the reason the central nervous system and brain evolved is twofold. The first reason is to enable the coordination of a creature’s internal elements. The second is to link perceptions of the outside world with effective actions. He argues that this second selective pressure arose only after the rise of predation — likely sometime in the Cambrian Period, approximately 540 million years ago — when it became necessary to perceive surrounding threats more acutely and develop the cognitive capacity to process and act on those perceptions).

On the Planet of the Apes, human-like intelligence is so adaptive that it is a convergent feature of evolution — species are waiting in the wings to move in and occupy the intelligence niche. (Yesterday, we posted a fascinating study that suggests that human intelligence is the result of a mutation of the human genome two million years ago).

Once there is life of any kind, Lineweaver asks “what is the probability that it will evolve into a human-like intelligence that can build and operate radio telescopes? We define intelligence this way not out of some geeky technophilic perversity but because posed this way, we have the ability to answer the question by searching for other telescopes with our telescopes. So far, no signals from intelligent aliens have been identified.”

The plot of the 1968 movie, “Planet of the Apes,” with Charlton Heston playing the role of Taylor, an astronaut on an interstellar journey. After traveling for over two thousand years at nearly the speed of light (during which the astronaut crew ages only 18 months due to time dilation), the spacecraft crash lands on a planet that has oxygen comprising 20 percent of the atmosphere, and a 23 hour 56 minute sidereal period.

Unsure of where in the galaxy they are, they soon discover that on this strange new world, chimpanzees and other primates have evolved to become human-like both physically and in the development of their society. Human beings, mute beasts that are captured and used for scientific experimentation, occupy a lower rung in this intelligence hierarchy.

This planet has corn, horses, and gorillas who use rifles and chimpanzees who use photographic equipment. It never occurs to them that this is, in fact, the Earth. Charlton Heston falls in love with a mute Homo sapien, and they ride away and discover the remnants of the Statue of Liberty. Only then do they realize this is planet Earth, there’s no going home. They’re there; as a subordinate species.

In an interview with NASA’s Astrobiology, Lineweaver emphasizes that the “Planet of the Apes” hypothesis is that “such a niche exists – that human beings developed a big brain because there was selection pressure to move into this evolutionary niche. Another way of saying it is that smart organisms are better off and more fit than stupider organisms in all kinds of environments, and therefore we should expect any type of critters anywhere in the universe to get smarter like we consider ourselves to be.

“Carl Sagan called them “functionally equivalent humans.” That’s what the SETI program has been based on. There is a big polarization in science between physical scientists like Paul Davies and Carl Sagan and Frank Drake on the one hand, and biologists like Ernst Mayr and George Gaylord Simpson who say that life is so quirky that human beings would never evolve again. If a species goes extinct, it doesn’t come back. There may be a niche that opens when a species goes extinct, but the same species or even anything similar to it does not re-evolve into that niche.

“If intelligence is good for every environment, we would see a trend in the encephalization quotient among all organisms as a function of time. The data does not show that. The evidence on Earth points to exactly the opposite conclusion. Earth had independent experiments in evolution thanks to continental drift. New Zealand, Madagascar, India, South America… half a dozen experiments over 10, 20, 50, even 100 million years of independent evolution did not produce anything that was more human-like than when it started. So it’s a silly idea to think that species will evolve toward us.

“If you go to these other continents and ask zoologists, Lineweaver continues, “What do you think is the smartest thing there? Is it trying to become human? Is it any closer today than it was 50 million years ago to building a radio telescope? I think the answer would be no. If that’s the answer, then there is no trend toward human-like intelligence, and this whole idea of intelligence being convergent is just an empty claim based on what we want to believe about ourselves.” Only one species of the billions of species that have existed on Earth has shown an aptitude for radios and even we failed to build one during the first 99% of our 7 million year history.

Current estimates say that are some 100 billion stars just in our Milky Way galaxy and 10 billion trillion stars in the observable universe.There are more stars in existence than days since the universe was formed.Yet, the deafening silence from space is not surprising. There must be other radio transmitters out there, but perhaps none in our galaxy. If homo sapiens survive long enough, time will tell.

We should not expect to see any other forms of life that are genetically, functionally and intellectually similar to us.” Lineweaver emphasizes. “I strongly suspect that our closest relatives in the universe are here on Earth, and they’re not likely to be elsewhere.”