Different species of hummingbirds have bills that vary in length and shape, matching the structure of the flowers on which they feed. Which of the following evolutionary scenarios best explains this diversity of hummingbird bill morphology?

W) Coevolution of flowers and hummingbirds, leading to specialization of hummingbirds on particular flowers

X) Random mutation of plants to develop varying flower shapes, and subsequent evolution of hummingbird bills to match these shapes

Y) Evolutionary race between flowers and hummingbirds, in which flowers become more extreme in shape to prevent nectar feeding

Z) Evolution of various bill shapes, since all hummingbirds opportunistically feed on many different species of flower, regardless of shape
W) COEVOLUTION OF FLOWERS AND HUMINGBIRDS, LEADING TO SPECIALIZATION OF HUMINGBIRDS ON PARTICULAR FLOWERS