One of the big questions is, "Where are the other intelligent species?" Since we exist, we would expect the universe to be teeming with other intelligent life. But, as Enrico Fermi remarked, "Where are they?"
There surely must be intelligent life on planets around other stars. The reaches of space are larger than most of us can really absorb. The Arecibo Radio Telescope could communicate with another copy of itself half way across our galaxy. But that communication would require us to know the exact location of the other civilization, and a round trip "hello" would take 100,000 years. Even if we searched the 5 billion stars in our half of the galaxy, we would still have covered only 0.00000000005 of the stars in the universe. The distances are enormous, to say the least. We may be isolated simply by the sheer scale of the universe.
The Earth is 5 billion years old, and the universe is 15 billion years old. There was plenty of time before us for advanced intelligence to develop. However, all of the chemical elements except Hydrogen and Helium can only be formed inside stars in the course of their fusion burning. For those atoms to get into a planet, the star where they formed had to explode and spew them out into space. This takes time, even though stars are massive and burned quickly when a galaxy is first formed. Planets with both rocks and water may not have been able to form in the early universe.
In the last ten years, astronomers have realized the importance of Gamma-Ray Bursters. They are the most energetic bursts of radiation in the universe. One kind of gamma-ray burst occurs when a massive and fast-rotating star collapses and becomes a black hole. Another kind occurs when a binary star system of two neutron stars runs down and the neutron stars hit each other. The amount of gamma-rays produced in a few seconds is sufficient to kill all multi-cellular animals in a large part of a galaxy.
Gamma-Ray Bursters are a reset button for higher forms of life, at least the kind of life that we know about. Gamma-Ray Bursters are less common now, as the universe gets older, and the massive stars at the centers of galaxies have burned out. On Earth, complex life needed about 700 million years to get to the current stage. Perhaps the last few billion years are the first time it has been quiet enough for complex life to develop and not be "reset" by a burster.
Yes, whales, elephants and African Gray Parrots are intelligent. Even dogs have a glimmer of it, although they strike me as being much closer to a human with a prefrontal lobotomy. But, I am not interested in animal intelligence. I am talking about a different level of intelligence. I am talking about being smart enough to be whipped into a war frenzy, and then smart enough to realize that this may not have been such a good idea. I am talking about discovering materials, preparing them and then using them. We build things; we invent and engineer; we write, accumulate knowledge, and do mathematics. My real measures of intelligence in a species are these: Have you classified the elements? Have you discovered chemistry? Have you decoded your own DNA or the equivalent?
Where are the species that do those things?
Let's consider human ancestors during the three million years it took them to go from pre-Chimpanzees to modern humans. They were hunter-gatherers out on the African plain. It took a long time to accumulate the right set of genes to be truly intelligent.
Now, let's replay history and make it a little harder for those pre-humans. Suppose that everything is the same, except that lions and hyenas can fly. At any time, a very large fast predator can dive from the sky, showing a full complement of sharp teeth. This danger makes it hard to concentrate on chipping and shaping a stone tool.
Speaking of stone tools, suppose the air is so viscous that a pre-human can not chip stones. The resistance of the air is so strong that a stone can't go fast enough to impact another and break off flakes. Stone tools and arrow heads are almost impossible to make.
How will early man catch animals to cook over his newly-tamed fire? No matter, in this scenario the air does not support burning. We will suppose that fire is not possible in this place. Besides missing cooked meat, and heat to liberate starch from tubers, there is no way to smelt ore into copper. And, no fire to make pottery. Things are beginning to look a little difficult.
Don't worry about the inability to make copper hand axes. The atmosphere is so corrosive that it rusts all metals to a powder almost immediately.
Add to this a lack of fences to keep animals out of the fields, and also no fences to keep domestic animals in. Since everything can fly, grazing animals just fly in over the fence and eat the crops. Likewise, domestic animals escape straight up into the sky. It is also extremely difficult to keep slaves of your own species.
Since everything can fly effortlessly, there is no "blessed isolation." There is no valley or plateau where a group can do things differently for many generations and not have to compete with everyone else.
To top it all off, early humans stored food by drying it. In this scenario, let's make drying impossible. The only way you can store food is by putting on fat. Fat can't be transferred from one person to another, so group sharing is difficult. Division of labor is difficult because the food gatherers can't share their food with others at a later time. Everything has to be consumed immediately and then it can't be given to another individual.
Why am I painting this weird picture?
Because this is the situation underwater.
I am arguing that human style intelligence is much more difficult to develop in the ocean. Underwater, predators can swim in and attack at any moment, chipping stone is almost impossible, throwing spears and rocks does not work, fire is impossible, metal ore can't be made into solid metal, protecting crops is difficult, domestic animals can't be corralled, true geographical isolation is hard to find, and food can't be stored by drying for later sharing.
This may explain why fish have been evolving for 410 million years and have not developed advanced intelligence. Monkeys developed intelligence after just 40 million years. A factor of 10 is compelling.
Both in the dinosaur world and underwater, there seem to be "strange attractors" that keep animals focused on speed and armor. This is a fancy way of saying that they get into a rut and stay there. Swimming faster is so important to a fish, that it is willing to give up having hands. Imagine giving up your hands. Seals and sea lions are actual examples of this. They did have hands (grasping paws), and gave them up in the course of going back to the sea.
I am arguing that dry land may be necessary for a species to develop human-level intelligence. There might an entirely different way to do it underwater, but I don't know what it is. The path would have to be very different. It is difficult to imagine how the ability to build things in a general way would be self-reinforcing underwater. Our path to intelligence was built on learning to use tools and objects. The marine world is simply not friendly to non-living "objects."
Perhaps we don't see alien intelligences because an Earth with dry land is unusual. This is one of the many "rare Earth" hypotheses. Perhaps there aren't very many planets with large amounts of dry land. Perhaps the normal earth-orbit planet is a water-world.
It is also possible that our own solar system is unusually rocky. Maybe it formed in an area with more heavy elements than usual. If rock were scarce in the average solar system, every planet would either be a a gas giant or be covered with water.
The absence of other intelligent life calls for some wild theories, and for some more unusual thoughts and approaches.
--Ted Kaehler.
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