“Survival of the fittest”. With this lapidary phrase, the theory of evolution by natural selection presented by Charles Darwin and Alfred Russell Wallace in the Linnaean Society of London in 1858 has been summarized for more than a century and a half. A scientific theory that led to the writing, the following year , from the famous book The Origin of Species.
However, the English naturalist never wrote anything about evolution being equated with survival of the fittest . He doesn’t even mention it to reject the idea. There is a quote falsely attributed to Charles Darwin, which says “it is not the strongest species that survives, nor the most intelligent. It is the one most adaptable to change. That statement actually paraphrases a quote from Leon C. Megginson of Louisiana State University.
According to Darwin’s “The Origin of Species”, it is not the most intellectual species that survives; it is not the strongest that survives; rather, the species that survives is the one that can best adapt and adjust to the changing environment in which it finds itself.
Leon C. Megginson, 1963
However, the content of the quote is correct. Interpreting the theory of evolution as survival of the fittest is a wrong conclusion resulting from a misunderstanding of what the theory of evolution teaches us.
That it is the fittest individuals that are most likely to survive seems like a truism, but sometimes it is not easy to deduce which creature is fittest or why . The greater or lesser fitness of a living being depends on its intrinsic characteristics, but also on the environment in which it finds itself, and sometimes several different traits can provide similar levels of fitness.
The multiple traits that grant aptitude
As an example, you can think of a group of foxes in a forest. A glaciation makes the forest disappear and the landscape is dominated by ice, snow and cold. A fox cub that is born with the longest and densest fur, or with a greater predisposition to accumulate subcutaneous fat, will have a better coat and be more fit than one that lacks those traits. But also the one with the white fur or the smallest ears —since it will lose less heat.
Therefore, we speak of the survival of the hairiest or the whitest, but not necessarily the strongest . In other cases, it could be survival of the quickest, the most cunning, the darkest, or the one with the best sense of smell.
Throughout the history of evolution, life has been increasingly complex and sophisticated thanks to the accumulation of these skills , strength is just one more trait among the many possible traits. But if the range of traits that accumulate increasing the complexity of organisms is so wide, can being simpler be a determining trait?
survival of the simplest
It is true that it is common for living beings to evolve from simple forms to more complex ones, but it does not always happen. It may happen that the environment does not favorably select the most complex organism , but rather the opposite. That generates a negative selective pressure on any feature that confers complexity and benefits the simplest organisms.
If that happens, we are in a scenario where any mutations that add new traits will not be favored, while mutations that remove traits will be. That is the case of some crustaceans called pentastomids. They are internal parasites of reptiles, birds and mammals, which lodge in the respiratory tract. Thanks to genetic analyses, today we know that they are part of the group known as maxillopods —which includes, among others, barnacles, sea acorns and copepods—; however, for more than a century and a half, since their discovery in 1836, they were classified as a separate group of animals.
Crustaceans have a strong exoskeleton of chitin, two pairs of antennae, and a variable number of pairs of legs; a complex ganglia-based nervous system; a digestive system with an esophagus, stomach, and intestine; and a respiratory system based on gills.
However, the pentastomids, due to their condition as internal parasites, have been shaped by evolution towards maximum simplicity.
Far from presenting the complexities of a barnacle or copepod body, that of a pentastomid has been reduced to the shape of a flattened worm. It has no legs, no antennae, no eyes; only two pairs of sensory papillae around the mouth, with small chitinous hooks with which it clings to its host. Their bodies are still covered in chitin, but it is a very thin layer and remains highly flexible . Its nervous system is similar to that of other crustaceans, although also simplified, with ganglia dedicated almost exclusively to the buccal region, the papillae and the reproductive system. The digestive system has also been simplified to a simple straight tube that empties into the anus. As for the respiratory apparatus , the pentastomids have reached the maximum degree of simplicity: they do not have it.
In that parasitic life that characterizes the pentastomids, the survival of the strongest, the most intelligent, the fastest and the most cunning did not apply. Under these conditions, the fewer unnecessary organs you have, the less energy is invested in forming them. It is a scenario where the survival of the simplest is applied.
REFERENCES:
Christoffersen, ML, & de Assis, JE 2015. Pentastomida. Ibero Accessible Entomological Diversity, 98A, 1-10.
Darwin, C. 1859. On the origin of species by means of natural selection, or, The preservation of favoured races in the struggle for life /. John Murray, Albemarle Street,. DOI: 10.5962/bhl.title.82303
Megginson, L. C. 1963. Lessons from Europe for American Business. The Southwestern Social Science Quarterly, 44(1), 3-13.
