arin finished the thought for him. "The mice weren't here when we got here. They were born of the squirrel-size omnivore."
Hafner nodded. "And the rats?"
"Born of the next larger size. After all, we're environment, too—perhaps the harshest the beasts have yet faced."
Hafner was a practical man, trained to administer a colony. Concepts were not his familiar ground. "Mutations, then? But I thought—"
The biologist smiled. It was thin and cracked at the edges of his mouth. "On Earth, it would be mutation. Here it is merely normal evolutionary adaptation." He shook his head. "I never told you, but omnivores, though they could be mistaken for an animal from Earth, have no genes or chromosomes. Obviously they do have heredity, but how it is passed down, I don't know. However it functions, it responds to external conditions far faster than anything we've ever encountered."
Hafner nodded to himself. "Then we'll never be free from pests." He clasped and unclasped his hands. "Unless, of course, we rid the planet of all animal life."
"Radioactive dust?" asked the biologist. "They have survived worse."
The exec considered alternatives. "Maybe we should leave the planet and leave it to the animals."
"Too late," said the biologist. "They'll be on Earth, too, and all the planets we've settled on."
Hafner looked at him. The same pictures formed in his mind that Marin had thought of. Three ships had been sent to colonize Glade. One had remained with the colonists, survival insurance in case anything unforeseen happened. Two had gone back to Earth to carry the report that all was well and that more supplies were needed. They had also carried specimens from the planet.