In the 1968 movie, "Planet of the Apes," Charlton Heston plays 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.

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 contemptuously used for scientific experimentation, occupy a lower rung in this intelligence hierarchy.

Charley Lineweaver, a cosmologist with The Australian National University, says the "Planet of the Apes" story is based on a flawed notion of evolution. In this interview with Astrobiology Magazine's Leslie Mullen, he explains how there is no evidence to support the idea that organisms inevitably become smarter over time, and why that is important in our search for life elsewhere.

Astrobiology Magazine (AM): Could you describe your "Planet of the Apes" hypothesis?

Charley Lineweaver (CL): In the movie "Planet of the Apes," Charlton Heston and his team land on a planet that has oxygen comprising 20 percent of the atmosphere, and a 23 hour 56 minute sidereal period. 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 anymore. We really screwed it up by killing ourselves, because these bad other creatures have occupied our rightful place in the intelligence niche.

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 and Jill Tarter and Seth Shostak 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.

AM: SETI is based on the theory that science development will be the same wherever you go, because the physical laws of the universe are the same everywhere. So you'll always eventually have scientists, doctors, technology.

CL: Exactly, but they have zero data to support that. It's based on what they think might happen in the future and what might have occurred elsewhere in the universe. That's not good enough for me. Scientists have to be evidence-based. So let's test this idea.

One test is Harry Jerison's work on the encephalization quotient as a function of time, and whether that increases in lineages that are independent of the human lineage. (The encephalization quotient, or EQ, is the brain-to-body-mass ratio.)

Harry Jerison is what I call a brain worshipper. He wanted to find that everything strives to become like us, but it's just not true. Sometimes brains do get bigger. Sometimes brains get smaller. You would see this kind of diversification for any feature. A common ancestor will have one type of nose, and when the species diverge some noses get smaller, some stay the same, some get larger.

The Jerison plot is used by SETI to show that there's some type of selection pressure towards increasing brain size. But if you choose any outstanding characteristic of a species and put it on a plot, you will get a climbing trend.

People point to dolphins as evidence that organisms get smarter. Our common ancestor with the dolphin probably lived about 80 million years ago. We could agree that this common ancestor had a small brain, although we have very sparse fossils. From this ancestor, both humans and dolphins independently evolved big brains. Actually, this is not an example of convergence because humans and dolphins have 3.5 billion years of shared common ancestry. For 98 percent of our history, humans and dolphins were the same. The genes needed to develop those big brains had been fine-tuned over billions of years of evolution and were already in place.

AM: When you look at the tree of life, humans and other animals with heads make up just one small part of it, and there are all these other branches that never even developed heads.

CL: That's right. Forget about brains, let's just talk about heads! If heads are a good idea, wouldn't they have developed in other phyla of life independently? And the answer is no, they appeared in one place, and all the other organisms are getting along perfectly fine, thank you very much, without heads.

When you look at the tree of life, it's really a bush. All the things that are alive today are on the top, and down on the bottom we have a convergence because all life evolved from some LUCA, last universal common ancestor. If you look at all the species 600 million years ago, there'd be only one that had a head. We now see them everywhere, but only because this one species radiated.

Species are quirky, like languages. The DNA sequence of one particular species is very unique. It's not something deterministic, like planetary formation. We're in the realm of biology, not in the realm of physics.

If heads are as quirky as a species, then you can ask yourself, do we expect Indian elephants in outer space? Not African elephants, but Indian elephants. Now, if you do not expect to find an Indian elephant on a planet orbiting Alpha Centauri, then you can not expect anything else that is species specific out there.

It's important to realize that building radio telescopes is a species-specific feature. Yet we insist on maintaining that this is something intelligence does in general. We've all been brainwashed into believing that our intelligence is so wonderful that every other species would want it, including all the extraterrestrials out there.

AM: It just seems logical that species will grow more intelligent over time, because of "survival of the fittest." A simple organism responding to its environment and learning more about it will do better than those that don't. In that light, a general trend toward greater intelligence seems like it would be an inevitable outcome of evolution.

CL: Well, consider the ancestor of the elephant. It had a little nose, and its nose was a little bit more sensitive than its neighbor's nose, and with that sensitive nose it was able to do things that its neighbor couldn't, so that nose became more sensitive and more tactile, and it got longer and longer and it did more and more things with it, and then it looks back at its own history and it says, "You know what, noses get bigger. Evolving a bigger nose was so useful to me, wouldn't that be a universally useful trait?"

AM: I've read that the ancestors of elephants were marine animals, and the nose developed as an oxygen periscope. So the development of that feature was specific to the needs of that environment. The assumption about the development of intelligence is that it would be a useful trait in every environment.

CL: You'd think so, but 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.

AM: Were the times of isolation of these land masses similar to the time needed for human brain development?

CL: The time scale for the development of a brain that accounts for the difference between our EQ and that of orangutans, chimps and gorillas took about 2 to 3 million years. These land masses were isolated for periods of time that were 10 to 30 times longer.

If you only had 20 million years of isolation, you'd have 10 times the amount of time you would need to develop intelligence, if our time scale is approximately average. Some of these places were not independent for 20 million years, however, they were independent for 50, 60, 90 million years. South America, for example, was independent of the lineages that led to us for about 100 million years before it ran into North America. Madagascar is still an independent experiment, as are New Zealand and Australia.

AM: Do you think time is the most important factor for the development of intelligence? If intelligence is not a general trend in all environments, then perhaps certain environmental conditions are necessary. If so, then it may be that most environments were such that species didn't need to develop that degree of intelligence.

CL: You could make that argument. It's hard to make up stories about what produced what in biology. Stephen Jay Gould called them "Just So" stories. He was always championing the idea of contingency. If he were alive today, I think he would say that if we were to all go extinct tomorrow, the chances of us evolving again are zero. And the chances of us finding a life form like us in outer space that we can have sex with and reproduce with are zero.

I come back to the point that radio telescopes are only made by human beings. We have not stopped species in New Zealand or Australia or South America from making radio telescopes. They had a long time to do it. It didn't happen. Now, one argument that my students sometimes give is that everyone is trying to do it, but we're just the first.

The evidence against that is, if you're seeing any type of trend toward human-like intelligence, you have to stop them sometime before they start building those radio telescopes.

If you go to these other continents and ask zoologists, "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.

AM: Do you see intelligence as a one-time accident of evolution?

CL: No, I think every species has its own type of intelligence. We have ours, elephants have theirs, dolphins have theirs. The type of intelligence they have is the type that has evolved in their quirky environment with all the genetic baggage that they have. To the extent that it's like ours is due to our shared ancestry. The idea that intelligence is a generic thing, and therefore others in outer space will have it too is just crazy, and it's wrong. There is no evidence for it on Earth, there's a lot of evidence against it, and as scientists I think we have to accept that.

AM: Yet you've said you support SETI, even though you think there's no chance of finding human-like intelligence elsewhere.

CL: The reason I support SETI is because I'm a scientist, and scientists look in places that haven't been looked in before. That is what SETI is doing. They're developing new instruments and new frequency ranges to look at astronomical objects in ways that have not been done before. That is the most powerful tool to discover something new in the universe.

I also support SETI because it inspires people. I think a lot of it is motivated for the wrong reasons, but so what? If people are motivated to find extraterrestrials, I think that's great. Give them a thousand dollars to build an instrument. The scientific exploration of the universe is a general goal that I think all scientists share. Also, I support SETI because maybe I'm wrong about this. People are wrong sometimes.

AM: There are some 100 billion stars just in our Milky Way galaxy and 10 billion trillion stars in the observable universe. There are probably planets associated with most of those stars. That would seem to increase the odds of finding another human-like intelligence out there.

CL: That's a tricky issue, because then you have to ask, what's the probability of a human being? What's the probability of you? Max Tegmark at MIT thinks he can calculate how far it is to the next you. The next Max Tegmark is living at 10 to the 10 to the 29th power meters away. It's mathematically complicated, so I probably shouldn't get into that. But consider a lottery.

This lottery doesn't have a thousand tickets or a million tickets, but an infinite number of tickets. Then pick a ticket. The probability of any one ticket being picked is zero, because the probability is one divided by infinity. But some ticket is going to be picked. So in that sense, everything that happens is impossible. That's a provocative way to state it, but I think there's some truth in that analogy.

But I still believe that the best evidence we have suggests that we should not expect to see human beings anywhere in the universe except Earth. We should not expect to see Indian elephants or any other forms of life that are genetically, functionally and cerebrally similar to us. I strongly suspect that our closest relatives in the universe are here on Earth, and they're not likely to be elsewhere.