Over long periods of time, many cave-dwelling organisms have lost their eyes. tapeworms have lost their digestive systems. whales have lost their hind limbs. how can natural selection account for these losses?3

Under particular circumstances that persisted for long periods, each of these structures presented greater costs than benefits. This is the reason why many cave-dwelling organisms have lost their eyes, tapeworms have lost their digestive systems and whales have lost their hind limbs. When the structures they had wer no more benefitial they slowly became other form.