Darwin’s theory of natural selection can be summarized as a claim about three facts and their consequences.
The facts:
1) Organisms vary in nearly everything that can be measured about them.
2) These differences often make a difference in terms of survival and reproduction (fitness).
3) Offspring tend to resemble their parents.
The consequences: When these facts pertain, populations of organisms tend to change their properties over time, as more fit traits tend to increase in frequency and less fit traits tend to decline.
These facts and their consequences are so obvious, if only in retrospect, that they must be true. History abounds with “Aha!” stories of revelations: Darwin remembering the exact spot on the road when it struck him. Wallace and his malarial fever. Huxley exclaiming “How stupid of me not to have thought of that!”
Notice that mathematics is not necessary to appreciate these facts and their consequences, any more than for the statement “if you kick a ball, it tends to move forward”. Math is important for discerning the consequences of assumptions in more complex cases and in more detail (such as the exact rate of change), but not for a simple case like this and to a rough approximation. The import of Darwin’s theory was recognized and explored decades before mathematical models began to be employed.
Notice also that the three facts admit exceptions, signified by the words “nearly”, “often”, and “tend”. Exceptions to the rule do not detract from the generality and explanatory scope of the theory.
These observations about the theory of natural selection are standard fare and it would be difficult to find an evolutionary scientist who does not agree with them. Rehearsing them, however, enables us to make a point about Multilevel Selection (MLS), which is far less settled as a theory. Let’s begin with Darwin’s famous speculation about the evolution of human morality.
It must not be forgotten that although a high standard of morality gives but a slight or no advantage to each individual man and his children over the other men of the same tribe, yet that an increase in the number of well-endowed men and the advancement in the standard of morality will certainly give an immense advantage to one tribe over another. There can be no doubt that a tribe including many members who, from possessing in a high degree the spirit of patriotism, fidelity, obedience, courage, and sympathy, were always ready to aid one another, and to sacrifice themselves for the common good, would be victorious over most other tribes; and this would be natural selection. At all times throughout the world tribes have supplanted other tribes; and as morality is one important element in their success, the standard of morality and the number of well-endowed men will thus everywhere tend to rise and increase.1
We need to overlook Darwin’s sexism as a creature of the Victorian age. Also, he is curiously silent on the glaring fact that morality within a group can result in harmful interactions between groups. Leaving these aside for the moment, Darwin is adding a small list of facts and their consequences to the three facts of natural selection listed above.
More facts:
4) Social interactions nearly always take place in groups (what Darwin called “tribes” in the passage listed above) that are small compared to the total evolving population.
5) Prosocial behaviors, which benefit others or one’s group as a whole, typically do not maximize the relative fitness of the prosocial individual within its group.
6) Groups whose members behave prosocially toward each other robustly have a relative fitness advantage, compared with groups whose members do not cohere.
The consequences: Prosocial behaviors can evolve when selection among groups in the total population outweighs selection among individuals within groups.
These facts and their consequences have the same simplicity as the three facts about natural selection. Math isn’t necessary and it doesn’t matter that the facts admit exceptions to the rule, denoted by the words “nearly” and “typically”.
Careful evolutionary thinkers have repeatedly affirmed the validity of Darwin’s reasoning for the evolution of prosocial behaviors. Here is Sewall Wright, one of the first to construct mathematical models of evolution, writing in 1945:
It is indeed difficult to see how socially advantageous mutations can be fixed without some form of intergroup selection.2
Here is George C. Williams, famous for critiquing sloppy thinking about evolution, writing in 1966:
It is universally conceded by those who have concerned themselves with this problem that…group-related adaptations must be attributed to the natural selection of groups of individuals and that the natural selection of alternative alleles within populations will be opposed to this development. I am in entire agreement with the reasoning behind this conclusion. Only by a theory of between-group selection could we achieve a scientific explanation of group-related adaptations.3
And here is how one of us (DSW) summarized the simple logic of MLS theory in a 2007 review article with Edward O. Wilson:
Selfishness beats altruism within groups. Altruistic groups beat selfish groups. Everything else is commentary.4
Given the certitude of these statements and the simple facts on which they are based, you might think that higher-level selection would be widely accepted as a requirement for the evolution of higher-level adaptations. Yet, that is far from being the case, as anyone familiar with the subject knows. Group-level selection was actually rejected as an important evolutionary force in the mid-20th century and today it coexists with an array of other theories of prosocial evolution, whose merits are debated in heavily mathematical terms. Outside the Ivory Tower, most people have never heard of MLS theory or have views about it that are sadly outdated.
Why is it important to recognize the simplicity and generality of MLS theory? Because it shows beyond doubt that the lower-level pursuit of self-interest often disrupts rather than benefitting the common good. In economic terms, this means that the metaphor of the invisible hand is profoundly untrue. All cooperative endeavors are vulnerable to what the ecologist Garrett Hardin dubbed “the tragedy of the commons” for the overexploitation of natural resources.
MLS theory tells us that we can evolve systems that function for the common good, but only by selecting at the scale of the whole system and suppressing the potential for disruptive lower-level selection within the system. Those three simple facts and their consequences can inform nearly every positive change effort, from small groups to the entire planet.
Other articles in this series will explore the turbulent history of MLS theory. The purpose of this article is to restore its simplicity and generality. The whole world needs to know that MLS theory is an extension of the theory of natural selection (not a bizarre deviation from it) that is required to explain the evolution of prosociality in all its forms.
Literature Cited
(1) Darwin, C. (1871). The descent of man and selection in relation to sex: Vol. 2 vol. John Murray (p 166).
(2) Wright, S. (1945). Tempo and mode in evolution: A critical review. Ecology, 26, 415–419 (p. 419).
(3) Williams, G. C. (1966). Adaptation and Natural Selection: A critique of some current evolutionary thought. Princeton University Press (p 91-92).
(4) Wilson, D. S., & Wilson, E. O. (2007). Rethinking the theoretical foundation of sociobiology. Quarterly Review of Biology, 82, 327–348 (p 345).
Related books and articles
Sober, E. (2024). The Philosophy of Evolutionary Theory: Concepts, Inferences, and Probabilities. Cambridge University Press. https://doi.org/10.1017/9781009376037
Sober, E., & Wilson, D. S. (1998). Unto Others: The Evolution and Psychology of Unselfish Behavior. Harvard University Press.
Wilson, D. S. (2024). Williams’ Rule and Its Relevance for Positive Change Efforts. This View of Life (peer reviewed) https://doi.org/10.5281/ZENODO.10826558
Header Image: Rembrandt van Rijn, "The Storm on the Sea of Galilee," via Wikimedia Commons
