Only the strong survive? Tell that to the dinosaurs. The rajasaurus pictured here lived at the very end of the Cretaceous period and despite its power, it and dozens of other carnivorous therapods were destined for extinction.
The idea that strength is the most prevalent survival trait is not even remotely based upon scientific observations, and draws primarily from people's beliefs about competition. But even accepting the rather limited view that competition is the sole aspect worth focusing upon (mistaking ubiquity for quintessence), strength is just one of many competitive advantages that can help a species survive (or indeed, an individual succeed).
The mythology behind the idea that “only the strong survive” relates not so much to biology, but rather to sociological metaphysics. The idea is associated with social Darwinism, which represents a range of different ideologies with very little in common beyond the belief in competition as the driving force in cultural evolution. The term is quite misleading, as it refers to many things which were formulated before Darwin published On the Origin of Species by Means of Natural Selection, including the ideas of the 18th century clergyman Thomas Malthus, as well as those of Darwin's cousin Francis Galton.
The trouble with social Darwinism is that it is entirely metaphysical – there is nothing testable in the idea of the primacy of competition, and it has lamentably been used to fuel all manner of abhorrent ideologies such as imperialism and racial supremacy. As we saw in the previous myth of evolution, luck has just as great a role in influencing biological evolution as strict competition, and the same is likely true in the social realm. Furthermore, it is readily apparent that even recognising numerous aspects of competition in society doesn't preclude a parallel recognition of the benefits of co-operation: if companies compete in the national marketplace, and nations compete in the international marketplace, it is important to remember that both the company and the nation represent examples of widespread co-operation. If this were not the case, all trade would be between individuals.
Returning to biology, and accepting the simplification briefly, we might say that the strongest (i.e. deadliest) species generally become top predator within a particular ecology – but survival for apex predators is extremely precarious. Animals in such a position depend upon the robustness of the entire food web they are embedded within for their survival. A fox may be stronger than a rabbit (in terms of the capacity to cause harm), but if something threatens the survival of the rabbit, the fox is equally threatened: predators (which we tend to think of as being “strongest”) inherit vulnerability from the species they prey upon when ecological equilibrium is lost. Rather than generating survival advantage, they actually suffer extreme disadvantages in survival during times of crisis, precisely because they are dependent upon the success of their prey species. Few predator species rack up more than a few tens of millions of years at the top before becoming extinct.
If you want to pick out in the abstract the trait most suited to long-term survival of a species (and even more so for a chain of successive species), it is not strength but adaptability. The bigger and stronger you are, the fossil record attests, the harder you fall. At the end of the reign of the dinosaurs, some 65 million years ago, it was the tiny yet adaptable mammals that gained the edge (roughly 10 of the 15 mammal families at the end of the Cretaceous survived), along with some of the smaller, more adaptable therapod dinosaurs, which diversified into modern birds. Being strong only gets you as far as the next cataclysm: being adaptable is a far safer long-term strategy.
Alternative myth: Survival of the Adaptable
Next Week: Myth #3: The Selfish Gene