Many theorists argued that communication with extraterrestrials would prove impossible, because human beings would have nothing in common with them. These thinkers pointed out that just as human bodies represented the outcome of many evolutionary events, so did human thought. Like our bodies, our ways of thinking could easily have turned out differently; there was nothing inevitable about how we looked at the universe.

Men already had trouble communicating with intelligent Earthly creatures such as dolphins, simply because dolphins lived in such a different environment and had such different sensory apparatus.

Yes men and dolphins might appear virtually identical when compared with the vast differences that separated us from an extraterrestrial creature--a creature who was the product of billions of years of divergent evolution in some other planetary environment. Such an extraterrestrial would be unlikely to see the world as we did. In fact, it might not see the world at all. It might be blind, and it might learn about the world through a highly developed sense of smell or temperature, or pressure. There might be no way to communicate with such a creature, no common ground at all. As one man put it, how would you explain Wordsworth's poem about daffodils to a blind watersnake?