What Would Aliens Look like?

At Big Think Dirk Schulze-Makuch has a couple of short essays in which he speculates on what intelligent alien life forms would like if such there be. He writes:

What do aliens look like? Inundated as we are with science fiction movies, where aliens come in all different shapes and sizes, one wonders what form a real extraterrestrial would take. You need only look at the diversity of life on our own planet, from bacteria to humans to oak trees, to get a glimpse of what might be possible.

The variety is amazing, even though all known life forms have pretty much the same biochemistry and all are based on DNA. Sci-fi directors might look further for inspiration, to extinct species like trilobites or the giant shark Megalodon. But the real pool of possibilities is surely many times greater.

When I was asked in a recent documentary on German TV how I would envision an intelligent alien, I suggested that they might look like a crow with little hands on the edges of their wings, maybe a bit more sophisticated than the claws that bats have on the end of their wings. In theory, that would allow the creatures to build things and become technologically advanced.

He goes on in another essay to speculate that,

Either way, we expect the extraterrestrials to be very different from us. It is implicit in the word we use to describe them: aliens.

If we venture into an inhabited universe, we are likely to run into beings that evolved under entirely different physical circumstances. Will we meet them as curious, friendly, fellow explorers? Predators and prey? Will we be delighted or disgusted by their strangeness?

We might be so confused by their otherness that we don’t even recognize them as living beings.

The view outlined by Schulze-Makuch in these essays is a common one - intelligent, technologically advanced beings from some other solar system or some other galaxy would have had a different evolutionary history and would thus obviously not look like us.

It's the popular view, but in his book The Miracle of Man geneticist Michael Denton argues very cogently that it's wrong. If there are intelligent, technologically advanced civilizations elsewhere in the universe the creatures who populate it would have to look pretty much like human beings.

Why?

Any life form in our universe must be subject to the constraints imposed by the chemistry and physics that governs this universe, and those constraints make it virtually necessary that intelligent, technologically advanced creatures have an ensemble of characteristics that in the end would make them look pretty much like we do.

They'd have to come from a planet similar to ours with copious amounts of water, an atmosphere with roughly the same percentages of oxygen and nitrogen, a temperature range suitable for life, etc. These factors would also constrain the anatomy and physiology of any creatures on the planet.

As Denton explains, for creatures to develop intelligence they have to be carbon-based - no other element including silicon, can substitute - and if they're carbon-based their biology will be similar to that of creatures on earth. To develop technology they'd have to be terrestrial creatures and oxygen breathers.

They'd likely have a brain similar to ours since ours has been found to be optimal for achieving the limits of biological intelligence, and unlike terrestrial apes, intelligent aliens would, like us, need to have a fully opposable thumb.

The creatures would also have to be able to use fire without which they never would've developed metallurgy and thus technology, but this means that they'd have to be able to secure and use fuel such as wood or coal. This would be very difficult if not impossible for any beings that lacked eyes, arms and hands. So, too, would tool use be difficult.

Bipedalism is also a necessity for any creature which uses tools, since it frees up the upper limbs, and achieving technology without using tools is incomprehensible.

Since the planet would have to be about our size its gravity would have to be about what ours is. This means that any creatures on it would have to be within a certain size range. They couldn't be too much smaller than are we because, inter alia, they would lack sufficient strength to hew lumber or mine ore.

Nor could they be much bigger since mass increases with the cube of one's height, but bone and muscle strength increase only with the square of the height. Thus, a much larger race of aliens would be less adroit and more fragile. Tripping and falling would be catastrophic (compare the fall of a toddler with the fall of an adult).

Denton explains much more and goes into much more detail in his book, but toward the end he says this:

Nature is uniquely fit not just for our biological being, for our aerobic terrestrial existence, and for our size and body plan, but also for our unique capacity for fire-making and for following the singular path through metallurgy to an advanced technology and a profound understanding of nature.

That claim can only be challenged by showing that, given the laws of nature and the structure of the cosmos, there is the possibility of fundamentally different types of biological life than ones based on carbon and water, the possibility of fundamentally different types of intelligent beings capable of making and controlling fire, and fundamentally different routes to an advanced technology and deep knowledge of the world, routes that do not pass through fire-making and metallurgy.

However, no credible alternatives of this sort have ever been proposed.

No single book or paper exists which provides a well-worked-out blueprint for a cell radically different from the canonical carbon-based cell, the basic building block of all life on Earth. No single paper or book exists which describes within the domain of carbon-based life an alternative biological design for an advanced organism comparable to modern humans possessed of a high metabolic rate and high intelligence.

Nor has an alternative design ever been proposed in any detail for an advanced intelligent aerobic organism capable of making and controlling fire. Nor is there a single paper which describes a substantially different route to an advanced technology and ultimately scientific knowledge.

One can imagine variations on the humanoid theme, of course, some more realistic than others. But to the degree that they are credible, they will be variations very close to the human form.

You can read a shorter summary of Denton's fascinating book here. Maybe somebody should send a copy to Mr. Schulze-Makuch.