We colonised Earth, in the reign of the great reptiles, who were dying when we came and whom we could not save. Your world was a tropical planet then, and we felt that it would make a fair home for our people. We were wrong. Though we were masters of space, we knew so little about climate, about evolution, about genetics...

For millions of summers--there were no winters in those ancient days--the colony flourished. Isolated though it had to be, in a universe where the journey from one star to the next takes years, it kept in touch with its parent civilisation. Three or four times in every century, starships would call and bring news of the galaxy.

But two million years ago, Earth began to change. For ages it had been a tropical paradise; then the temperature fell, and the ice began to creep down from the poles. As the climate altered, so did the colonists. We realise now that it was a natural adaptation to the end of the long summer, but those who had made Earth their home for so many generations believed that they had been attacked by a strange and repulsive disease. A disease that did not kill, that did no physical harm--but merely disfigured.

Yet some were immune; the change spared them and their children. And so, within a few thousand years, the colony had split into two separate groups--almost two separate species--suspicious and jealous of each other.

The division brought envy, discord, and, ultimately, conflict. As the colony disintegrated and the climate steadily worsened, those who could do so withdrew from Earth. The rest sank into barbarism.

We could have kept in touch, but there is so much to do in a universe of a hundred trillion stars. Until a few years ago, we did not know that any of you had survived. Then we picked up your first radio signals, learned your simple languages, and discovered that you had made the long climb back from savagery. We come to greet you, our long-lost relatives--and to help you.

We have discovered much in the eons since we abandoned Earth. If you wish us to bring back the eternal summer that ruled before the Ice Ages, we can do so. Above all, we have a simple remedy for the offensive yet harmless genetic plague that afflicted so many of the colonists.

Perhaps it has run its course--but if not, we have good news for you. People of Earth, you can rejoin the society of the universe without shame, without embarrassment.

If any of you are still white, we can cure you.