The economics of evolution: Henry Ford and the Model T

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For the past 30 years evolutionary biologists have used a fictional tale about engineer and businessman Henry Ford to help illustrate the undesirability of over-design. Thus, on discovering that kingpins were rarely damaged in scrapped Model T automobiles, Henry Ford is alleged to have concluded that the kingpins were unnecessarily durable and asked that they be built to a cheaper specification. The general lesson that has been drawn from this tale is that natural selection will act to equalize the mortality risks accruing from damage to each part of the organism's body. Yet it is well known, at least as far as humans are concerned, that death is more likely to be attributed to a failure of some organs compared to others. To understand why this might be so, we use some graphical and mathematical models to show that even if all body organs were equally important to survivorship, then the optimal investment solution that maximizes whole-organism longevity will typically not be the solution that equalizes the fail-times of the individual organs. As with natural organisms, the key to any optimal investment policy in multi-component systems is understanding what ‘bang you can get for your buck’. Moreover, we use a specific model to show that, even following selection to ameliorate the effects of damage, those body parts that receive more damage are still more likely to be the ultimate cause of death – that is, there is ‘under-compensation’. Therefore, the decision to make the kingpins more cheaply should not have been based only on the fact they rarely cause car failure compared to other car components. Such arguments wrongly assume that if one car part (or body part) is less durable than the others, then it will always be the reason for any future breakdown (or death).