Suppose that this evening a spaceship from somewhere outside the solar system landed unnoticed in your neighborhood. Suppose you saw three beings from that ship walk down the road in front of your house at dusk. Would you run screaming to the telephone to call the police? No, the chances are that you wouldnt even give them a second look.

　　We can be almost certain that our visitors from space will not have three eyes, webbed feet, or television antennae growing out of their foreheads. Instead, scientists theorize, they will probably bear a strong resemblance to the man next door.

　　The reason we can make this assumption is that science has shown that the shape of a living body is not accidental.

　　There are rules of biological construction that help us picture presumed visitors before they actually step out of their spaceship.

　　In applying the rules, we have to make just two assumptions. The first is that the bodies of spacemen consist of protoplasm like ours. The second is that they are intelligent, which is an inescapable fact once we accept the idea that they are capable of building a spaceship.

　　With those assumptions in mind, we can paint this portrait of the man from Planet X. :

　　He breathes air. Water breathers might develop some intelligence, but they could not smelt metals under water. This means that any development above the level of our own Stone Age is the accomplishment of air breathers.

　　He eats both plants and meat. A strict plant-eater spends too much time stuffing himself with food to build the kind of civilization which is necessary to produce a spaceship. Animals which can digest meat only would not be likely to survive the occasional adverse periods which very likely occur on all planets and wipe out the less adaptable forms of life.

　　Hes probably not much larger than the largest human being. The limiting factor here is something called the spare-cube law. If you double the height of a, person without changing his proportions, you have a being with weight times the weight. This means that a person 12 feet tall, for example, must be clumsy and cannot perform precision work. And precision work will be essential, of course, in building the spaceship.

　　He weighs at least 40 pounds, and probably more. A brain of a certain size and complexity would be required for the building of a spaceship. The brain of our spacemen would weigh at least 2 pounds.

　　Suppose that this evening a spaceship from somewhere outside the solar system landed unnoticed in your neighborhood. Suppose you saw three beings from that ship walk down the road in front of your house at dusk. Would you run screaming to the telephone to call the police? No, the chances are that you wouldnt even give them a second look.

　　We can be almost certain that our visitors from space will not have three eyes, webbed feet, or television antennae growing out of their foreheads. Instead, scientists theorize, they will probably bear a strong resemblance to the man next door.

　　The reason we can make this assumption is that science has shown that the shape of a living body is not accidental.

　　There are rules of biological construction that help us picture presumed visitors before they actually step out of their spaceship.

　　In applying the rules, we have to make just two assumptions. The first is that the bodies of spacemen consist of protoplasm like ours. The second is that they are intelligent, which is an inescapable fact once we accept the idea that they are capable of building a spaceship.

　　With those assumptions in mind, we can paint this portrait of the man from Planet X. :

　　He breathes air. Water breathers might develop some intelligence, but they could not smelt metals under water. This means that any development above the level of our own Stone Age is the accomplishment of air breathers.

　　He eats both plants and meat. A strict plant-eater spends too much time stuffing himself with food to build the kind of civilization which is necessary to produce a spaceship. Animals which can digest meat only would not be likely to survive the occasional adverse periods which very likely occur on all planets and wipe out the less adaptable forms of life.

　　Hes probably not much larger than the largest human being. The limiting factor here is something called the spare-cube law. If you double the height of a, person without changing his proportions, you have a being with weight times the weight. This means that a person 12 feet tall, for example, must be clumsy and cannot perform precision work. And precision work will be essential, of course, in building the spaceship.

　　He weighs at least 40 pounds, and probably more. A brain of a certain size and complexity would be required for the building of a spaceship. The brain of our spacemen would weigh at least 2 pounds.