Chapter 7 unveils aConvergent evolution counterintuitive source of natural diversityNatural diversity: divergent evolutionDivergent evolution occurring hand in glove with classical convergent evolutionConvergent evolution. Contradictory phenomenaPhenomenon account for even greater diversityDiversity in natureNature. For example, if we change the shapeShape of a ductDucts to decrease fluid frictionFriction (to reduce pumping powerPumping power, desirable) we also diminish the thermal contact required for effective heatHeat transfer from the ductDucts wall to the flowFlow (undesirable, costly). This disadvantage is known as the ‘analogy’ between heatHeat transfer and fluid frictionFriction. Surprisingly, in warm-blooded animalAnimal designDesign the analogy is an advantage: body modifications have two desirable effects, reduced frictionFriction (reduced powerPower use) and reduced body heat lossBody heat loss. It is as if natureNature discovered how to convert the disadvantage (the analogy) into an advantage.