He did not believe that there was any biological form, however strange, which he could not accept in time and, perhaps, even find beautiful. The mind, not the body, was all that mattered. (3.9)
The quote ties in the themes of appearance and morality. As we said in our discussion of morality elsewhere in this section, the basis of morals in Childhood's End is reason. And reason says appearance is not important, but rather how a person, alien, or whatever, thinks.
It would probably be true in your case, but you must remember that most of the world is still uneducated by any reasonable standards, and is riddled with prejudices and superstitions that may take decades to eradicate. (4.59)
But that whole education thing takes time; it's not something that happens over night. Although given the history of humanity and racism—or is that speciesism?—we'd say fifty years is a generous timeline.
"[…]: the men of that age will be more stable than their grandfathers. We will always have been part of their lives, and when they meet us we will not seem so—strange—as we would do to you." (4.129)
The novel suggests that learning to look past appearances is really just making knowledge about appearances commonplace. The more you're around something, the less odd it feels.
There was no mistake. The leathery wings, the little horns, the barbed tail—all were there. The most terrible of all legends had come to life, out of the unknown past. Yet now it stood smiling, in ebon majesty, with the sunlight gleaming upon its tremendous body, and with a human child resting trustfully on either arm. (5.18)
The appearance of the Overlords directly ties into the many symbols and images of religion, especially Christianity. Hop over to our "Symbols" section for a whole discussion on how that fits into the story.
In the Middle Ages, people believed in the Devil and feared him. But this was the twenty-first century: could it be that, after all, there was such a thing as racial memory? (6.12)
The novel is posing a question to the reader, and while the story takes a few stabs at answering this question, it ultimately leaves the answer open for you to answer yourself. Is our fear of things, creatures, and even other people who do not look like us genetic? Can our mind overcome our genes?
Jan Rodricks, though he seldom appreciated his luck, would have been even more discontented in an earlier age. A century before, his color would have been a tremendous, perhaps an overwhelming, handicap. Today, it meant nothing. (8.2)
The Civil Rights movement had yet to get in full swing in the early 1950s when the novel was written. So the idea that a person of African descent could live in equality with someone of European descent—anywhere in the world—was definitely the stuff of the future (ugh to the 1950s).
They would never know how lucky they had been. For a lifetime, mankind had achieved as much happiness as any race can ever know. It had been the Golden Age. But gold was also the color of sunset, of autumn: and only Karellen's ears could catch the first wailings of the winter storms.
And only Karellen knew with what inexorable swiftness the Golden Age was rushing to its close. (14.38-39)
For this to be considered a Golden Age, it needed the detail that it was one for "any race." After all, if you look at so-called utopian ideals in the past, the Golden Age really only works for the race running the show.
[Thanthalteresco] might himself be putting on a superb act, following the performance by logic alone and with his own strange emotions completely untouched, as an anthropologist might take part in some primitive rite. (17.39)
The Overlords never truly integrate with humanity in a way that, say, American culture integrated so many different cultures to create something truly new. Instead, the Overlords are always on the outside of humanity looking in, like the anthropologist imagery above suggests.
To all outward appearances, [Jennifer] was still a baby, but round her now was a sense of latent power so terrifying that Jean could no longer bear to enter the nursery. (19.4)
Appearances can be deceiving. That may be a cliché thing to say, but it holds true for Childhood's End—the Overlords look like devils, but they are scientific, not spiritual, creatures; Jennifer may look like a human baby, but she is anything but human.
"Everything we ever achieved has gone up there into the stars. Perhaps that's what the old religions were trying to say. But they got it all wrong: they thought mankind was so important, yet we're only one race in—do you know how many? Yet now we've become something that you could never be." (24.51)
Humanity is unique in the universe in that there is no other species like it elsewhere. Then again, you can say that about the Overlords, too. In fact, is there any species you couldn't say that about? Probably not. And in Childhood's End, alien races symbolize other cultures and races of Earth.