Carrie Arnold writes:

Thousands of miles from home in the steamy Amazon rainforest in the mid-1800s, the British naturalist Henry Walter Bates had a problem. More than one, really; there were thumb-size biting insects, the ever-present threat of malaria, venomous snakes, and mold and mildew that threatened to overtake his precious specimens before they could be shipped back to England. But the nagging scientific problem that bothered him involved butterflies.

Bates had noticed that some of the brightly colored Heliconius butterflies in the forest didn’t flit about like the rest; they moved more slowly. When he captured them and examined them under his makeshift microscope, he discovered that they weren’t really Heliconius at all, but astonishing look-alikes from unrelated families of butterflies.

By the time Bates’ discovery reached the scientific cognoscenti in England, Charles Darwin’s then-new proposal of natural selection could explain why this brilliant mimicry occurred. Birds and other predators avoid Heliconius butterflies because they are toxic to eat, with a bitter taste. The mimics were not toxic, but because they looked so much like the foul-tasting Heliconius, they were less likely to be eaten. The closer the resemblance, the more potent the protection.

What Bates and many later evolutionary biologists couldn’t explain was how this mimicry was possible. Getting the right shades of aquamarine and fiery orange in the right places on the wings required a constellation of precisely tuned genes. Those traits would have to be inherited with perfect fidelity, generation after generation, to preserve the Heliconius disguise. Maybe real Heliconius butterflies could afford to deviate a bit in coloration because their toxins could still teach predators to stay away in the future, but the mimics needed to be consistently flawless replicas. Yet the random reshuffling and remixing of traits in sexual reproduction should have quickly disrupted the essential coloring patterns. [Continue reading…]