In the course of reading sci-fi over many decades, I have encountered many different varieties.

I have seen intelligent life on other planets represented as gas, slime, blobs, mechanised beings, shape changers or humanoids.

The humanoids usually have big heads, slender bodies, huge eyes and elongated tapering limbs. Some have tentacles, others hands and feet.

It is possible that through the zillions of planets in the universe that we are the only intelligent life. The Earth may be an oasis in a vast desert.

On the other hand, it is also possible that life may be a common occurrence.

As a biologist, I am intrigued.

The earth has existed for a little over 4.5 billion years. It took just short of 2 billion years for the first life to evolve. For the next 2 billion life was merely a bacterial slime. All life on the planet probably evolved from one single instance – a protein/RNA combination. DNA would probably have evolved later.

2.4 billion years ago these bacteria started forming oxygen as a bi-product and transformed the atmosphere so that aerobic respiration could occur and organisms become more efficient and more complex. 2 billion years ago the first complex cells developed.

530 million years ago the first vertebrates appeared.

4 million years ago hominids appeared on the scene.

1.8 million years ago Homo sapiens evolved.

Of course, we are not the only intelligent creatures on the planet. Intelligence is hard to define and we tend to anthropomorphise it.

If we replace intelligence with consciousness then we are inundated. It is even possible that plants have consciousness.

When I look at a human being I see this strange evolution reflected in their morphology. We are modified fish.

But what if RNA had never interacted with protein? Is it possible for some other form of life to have developed? Does it have to be based around carbon?

I have seen theories of other elements but carbon is very useful.

Even if life developed in a similar way does it have to have a four-base DNA code? Could it be six?

When it reached the multicellular stage did it have to develop into a fish? Could it have gone down another route?

If it was a fish did that have to evolve into a quadruped and then a biped?

Evolution is a blind process – which is why our bodies are stuck with so many faults. Those faults – things like our one airway, our fragile necks and exposed brain, our digestive tract confused with our airway at one end and reproductive organs at the other – all could have evolved differently to create more efficient bodies. They didn’t. But perhaps elsewhere in the universe, they did.

Perhaps aliens do not have their brains stuck out on a fragile neck? Perhaps they are not based on the pentadactyl limb – formed from fins? Perhaps their reproductive system is separate from their excretory system and they have multiple airways?

I do not believe that ‘real’ alien life would be found in amorphous clouds of particles or slime. I think it would have a body and organs. But as to whether that body would resemble human beings? That I doubt very much.

It makes it fun to design an intelligent animal that evolved in a totally different way. That allows the imagination to work on what it might look like.