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Can eagles have sharper eyes? Or cheetahs run even faster? Or must the evolution of any adapted trait in nature reach a limit? (continued)

Pat French
Longdon-upon-Tern, Shropshire, UK

Evolution isn’t the pursuit of some ultimate superpower; it tends towards the optimal.

A cheetah lives in balance with the prey population in its environment. Any development that increased speed would come with a cost. Its musculoskeletal system is a balance between mass and energy delivery. More muscle would require increased bone mass to support it, both developments requiring more food input, more hunts and more prey. This would require a bigger territory to support each animal, which would reduce the potential cheetah population in a given area.

An eagle could possibly develop finer eyesight, a spider could possibly develop a stronger web system. But until their environment exerts a pressure for change, why should they do so?

Mike Follows
Sutton Coldfield, West Midlands, UK

It would be unusual for a species to become overdesigned – for instance, by evolving visual acuity far exceeding what is required for survival and reproduction.

Evolution operates through trade-offs, not towards perfection. This is why organisms can appear to be optimally engineered when, in fact, their traits represent compromises shaped by competing selective pressures.

An individual born with a heritable variation that confers even a slight advantage will tend to pass it on to its offspring – unless chance intervenes. Yet the metabolic and developmental costs of an enhancement, such as a more sophisticated eye, may outweigh its benefits. The same energy might be better spent on something else – for example, more elastic ligaments that enable a cheetah to change direction rapidly without injury.

Bone tissue exemplifies such compromises. It is exceptionally strong under compression and tension, but relatively weak under torsion and shear. In practical terms, a twisting force is more likely to cause a fracture than a comparable compressive load. To resist torsion more effectively, bones would need to be thicker or differently structured, increasing their mass. Birds with such bones would be too heavy to fly efficiently, and land animals would sacrifice speed and agility – a clear disadvantage for both predator and prey.

Simon McLeish
Lechlade, Gloucestershire, UK

Wild animals don’t live in a vacuum: they are part of the environment, forming an ecosystem. At any moment, that ecosystem is a pattern of tensions around the abilities of the animals within it, which means changing one aspect may have an effect on the whole ecosystem.

So, looking at the cheetah, if it ran faster, it may become exhausted more quickly in the chase, be more prone to overheating or be less able to turn sharply to follow a fleeing animal as it dodges to get away.

Evolution is driven by chance mutations. Some may result in a slightly different muscle protein, or some other difference, but any increased pressure on the antelopes the cheetah eats would change the whole ecosystem. One of the antelope species in the area may have recessive genes that allow it to turn more sharply, say. Individuals with that trait may become the dominant type and, potentially, a new species will arise. This is why human intervention in the environment can be catastrophic for animals: the change is often so rapid that the ecosystem becomes unviable, and extinction is the result.

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