Selection for Survival

“ Darwin’s grand idea of evolution by natural selection is relatively simple but often misunderstood. Since the environment can’t support unlimited population growth, not all individuals get to reproduce to their full potential.”

—Isabelle

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Selection For Survival

By: Isabelle Torres Santos

_____Isabelle_____

Natural selection is one of the basic mechanisms of evolution, along with mutation, migration, and genetic drift. Darwin's grand idea of evolution by natural selection is relatively simple but often misunderstood. Since the environment can't support unlimited population growth, not all individuals get to reproduce to their full potential. In this example, green beetles tend to get eaten by birds and survive to reproduce less often than brown beetles do. End result: The more advantageous trait, brown coloration, which allows the beetle to have more offspring, becomes more common in the population.

Charles Darwin and Alfred Wallace are the two co-discoverers of natural selection (Darwin & Wallace 1858), though, between the two, Darwin is the principal theorist of the notion whose most famous work on the topic is On the Origin of Species (Darwin 1859). Much like breeders choose which of their animals will reproduce and thereby create the various breeds of domesticated dogs, pigeons, and cattle, nature effectively “selects” which animals will breed and creates evolutionary change just as breeders do. To use one of Darwin’s own examples, wolves with especially long legs that allow them to run more quickly will be more likely to catch prey and thereby avoid starvation and so produce offspring that have especially long legs that allow them, in turn, to breed and produce still more long-legged descendants, and so on. Multiple bouts of Darwin’s process involving different traits, acting sequentially or in concert, may then explain both how speciation and the evolution of complex adaptations occur through the gradual evolution (change over time) of natural populations. Darwin aimed to convince his audience that even such structures as the vertebrate eye, which at first seem explicable only as the product of design, could instead be explained by incremental, directional evolution, a complex but still naturalistic process (Darwin 1859: ch.

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_____Isabelle_____

One usage, the “focused” one, aims to capture only a single element of one iteration of Darwin’s process under the rubric “natural selection”, while the other, the “capacious” usage, aims to capture a full cycle under the same rubric. Okasha interprets the covariance of offspring number and offspring phenotype as quantifying the causal influence of selection (Okasha 2006: 28) Clearly, these uses of “natural selection” are meant to capture only an element of Darwin’s process; As discussed further below, controversies over the focused notion of selection have to do with whether the focused notion of selection can be distinguished from that of drift (section 3), and whether selection, in the focused sense, should be counted as a cause (section 5). Because Darwin’s process is cyclical, specifying what is sufficient for a single cycle of it, a single instance of, say, replication of genes for long legs caused by long-legged wolves making narrow captures, is sufficient to specify a process that may explain adaptation and speciation. The capacious notion, capturing a cycle of Darwin’s process, is used by Lewontin and later authors working in the same vein, who put forward conditions for evolution by natural selection: these include variation, inheritance, and reproduction. While falling within the scope of “natural selection” in the capacious sense used by Lewontin, these elements of Darwin’s process are treated as distinct from natural selection when that notion is used in its focused sense.

Sources: "Mechanisms: Natural selection - Understanding Evolution." https://evolution.berkeley.edu/evolibrary/article/evo_25​. Accessed 25 May. 2020. "Natural Selection (Stanford Encyclopedia of Philosophy)." 25 Sep. 2019, https://plato.stanford.edu/entries/natural-selection/​. Accessed 25 May. 2020.

"Darwin, evolution, & natural selection (article) | Khan Academy." https://www.khanacademy.org/science/biology/her/evolution-and-natural-selection/a/darwin-evolution-nat ural-selection​. Accessed 25 May. 2020.

"10.36 Natural Selection and Populations Advanced - cK-12." 11 Dec. 2015, https://www.ck12.org/book/ck-12-biology-advanced-concepts/section/10.36/​. Accessed 25 May. 2020.

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