by David L. Duffy
Mayo’s book is a meditation on/updating of Ferdinand Brunetière’s (1894) The morality of evolutionary theory.  Like Christian de Duve’s Genetics of original sin and the future of life, Brunetière reckons Original Sin is explained by natural selection.  Mayo, however, prefers the Humean line on is-ought.
This is an “outsider” book on ethics, in the antiquarian v. historian sense. That is, it is written by a biometrical geneticist (whom I know slightly) with a keen interest in the history and philosophy of science. It comprises four short chapters and the author’s translation of Ferdinand Brunetière’s La Moralité de la Doctrine Évolutive (1896).  The first chapter starts:
The writing of this book was inspired or at least initiated by the reading of a short book by Ferdinand Brunetière, Writing in 1894, Brunetière considered the arguments about the direction of human evolution. He noted that biologists such as T.H. Huxley had established that progress was not a necessary consequence of change occasioned by natural selection, and that, indeed, regression was possible…[Unlike] Darwin [who] appears always to have held the view…that ‘all corporeal and mental endowments will tend to progress towards perfection’,…[i]t was clear to Brunetière that Man has fallen…Brunetière wrote ‘science enquires only into the “how” of things, never into the “why”’, but this a ‘disastrous error’.
[M]y goal is to see whether evolution…guides us or perhaps forces us to particular ethical positions…This question has two components. First, can anything in biology have ethical implications: is biology relevant to ethics? Secondly, if the answer to the first question is yes, what evolutionary facts, processes or theories…? I also begin by accepting the reality of the ‘naturalistic fallacy’.
The key genetic concepts introduced in this chapter are heritability and additive genetic variance, estimates of which Mayo uses as evidence that particular human behavioural traits exhibit between-individual differences due to genetic variation, and as such will respond to natural selection. He also includes a long section from R.A. Fisher’s The evolution of the conscience in civilised communities: In special relation to sexual vices, that diagnoses the large changes in Roman moral sentiments about infanticide and rape by 300 AD as entirely due to social factors.  This is contrasted with the Thornhill and Palmer evolutionary psychological analysis of rape in Chapter 2, which Mayo finds unimpressive. 
Chapter 2 introduces basic concepts that Mayo thinks he can wield to address his questions: consciousness, belief, discrimination (i.e. perception), naturalization and axiomatization of ethics, natural selection and how it can be invoked in the case of utility, values and their optimization, and what kinds of inference might legitimately be made from history and scientific models. In the latter case, he reviews one of his earlier papers on Feldman and Eshel’s model for the genetics of “altruism”; that a minimal model is constrained by biology to involve two linked genes. Each of these topics is huge, and the coverage brief.
Chapter 3 summarizes evidence that behaviors under the purview of ethics, such as the seven deadly sins, suicide, cooperation, cheating and altruism, are heritable in nature and as such are evolvable. These are mixed up with more abstract considerations, such as the evolution of language, Dollo’s Law (that the exact path of evolution is irreversible), and extinction. In the section on size, he quotes J.B.S. Haldane on the right size society: “To the biologist the problem of socialism appears largely as a problem of size. The extreme socialists desire to run every country as a single business concern. I do not suppose that Henry Ford would find much difficulty running Andorra or Luxembourg…” Mayo then goes on to argue that insect and animal societies are not very useful model systems for working out an optimal human community size.
Chapter 4 is called “Lessons.” Since Mayo does not explicitly review all of Brunetière’s essay, it is useful to read this through in parallel. The first section is “The Fall,” which Mayo succinctly states as a naturalistic hypothesis halfway through as “The corruption of Man’s Heart i.e. the imperfection of humans is [simply due] to…natural selection, which works on the available material.” Brunetière is sarcastic about the idea of a basically nice human nature as exemplified by Diderot’s “If you propose to be a tyrant over men…civilize yourself; drive yourself mad from an improvement of a morality contrary to nature…” That human short-termism usually trumps acting on the long view is an evolved bug, according to Brunetière, not a feature.
Brunetière is equally scathing about the Social Darwinists and other “strange moralists” like Guyau, who thought he could derive a morality “without obligation or sanctions” from Darwinism.  The “development of all our powers” and “expansion of all our potential” that Guyau sees as the evolutionary telos reduces in practice to “the law of the strongest or most skilled…what is natural…but precisely what is not human.” Later Brunetière quotes Spinoza:
Fish are required by their nature to swim, and the big ones are required to eat the small ones. That is why water belongs to fish, and the large eat the small by natural right. It follows that each being has a sovereign right over all that it can…And we admit in this regard no difference between men and other beings. 
Brunetière offers a naturalistic group evolutionary counterargument that “this has no more than the appearance of logic and or truth to be found in the hypothesis of the absolute fixity of species. Species vary? And in varying they sometimes perfect themselves?…Obstinacy of the individual will slow down the evolution of society [and thus perfection of the species]…. And, interruption of social evolution blocks the development of the individual. I suspect Mayo does not hold with group level selection. He doesn’t spend time directly on it in this section, even though he does mention in his conclusion that an ecosphere-directed ethics might avoid human extinction. He comments (as have many others) that extinction is common and perfectly natural, and does not see any “evolutionary ethical injunction” against humans sending themselves extinct.
As to “Why” and “How,” Brunetière is interested in teleological approaches to biology, citing Claude Bernard with gusto: “in every living embryo, there is a creative idea which develops and manifest itself through organisation,” he writes. “The physicists and chemists can omit any ideas of final causes in the facts they observe, while the physiologist is forced to admit an harmonious and pre-existing finality in the organism.”
The key sentences in Mayo’s summing up are: “As I hope I have made it clear, we cannot erect a theory of ethics from natural selection as we now understand it. Brunetière would not have been concerned by this conclusion.” The rest of that section run over the ideas including some like those of Savulescu and others regarding biological re-engineering for the creation of a more ethical human. For example:
Thirdly, rewire the brain. It is not clear if the tools are available, even if, as in the case of eugenics, we knew what to do…: general improvement in one trait will have correlated responses, and we do not in general know how, say, a general decrease in envy will influence behaviour in the large.
Brunetière finishes by saying:
[T]he morality that one can draw from evolutionary theory will never be more than a kind of ‘refracted’ morality, of which we always have to seek elsewhere the origin or source of illumination. Our animal descent…would not create real ‘duties’, and the consequences our deeds can have for the future of the species will never be a real ‘sanction’. But is it not something to have been forced by the theory of evolution into a fresh examination of the problem of morality?… Finally, if we have shown that outside of moral progress, all ‘progress’ is no more than an illusion or a chimaera, and that this is the teaching of evolutionary theory, would we not have been rewarded enough..? [T]hat man, as a man, is certainly placed in nature ‘like an empire within an empire’, that would not be a result so despicable as to have wrung the confession out of science as out of nature.
I’ll make a few general comments of my own. Heritability has its most concrete realization as the predicted size of the response to artificial selection, which underlies modern farming of both plants and animals. That is, we know it is a meaningful concept in that setting. If heritability is non-zero, there are relevant genetic differences between individuals that can be used to select “high genetic merit” population members to breed from. Some traits are heritable but also plastic, so we can imagine that both genetic change in the population over time – or a permanent change in the environment – could lead to exactly the same shift in the population average trait. More complex setups are also known to occur, where phenotype changes in response to environmental change, and genetic changes subsequently make that new phenotype level physiologically easy to maintain. So the seven deadly sins could have been selected for or against in the past or right now, but do not seem conspicuously absent in the modern world.
Theofanopoulou et al report an interesting comparison of genomic changes in “self-domesticated” species including humans, and flag a number of genes that have undergone positive selection, and so might underlie pro-sociality.  If these have become fixed in anatomically modern humans (that is, no between-individual variation at these sites), then an absence of variation means there is no heritability due to these loci. This leads to a common remark about human behavioral genetic studies where heritability of most traits (including those discussed by Mayo) is around 50%, namely that these traits can’t be very important. In studies of other animals, heritabilities are often lower. Note that genetic variants may undergo a “soft” or partial sweep, so that both “anti-social” and “pro-social” versions could be seen in different individuals from the same population. In the case of the rs23313128 polymorphism in the dog, the A allele increases sociability with humans and is at a frequency of 50% in dogs, and 0% in wolves.  All of this really depends on the nature, strength and directionality of selection pressure over time and place. The strong human genomic selection signatures that point to the nature of the selecting agent are for phenotypes like skin color (UV exposure, Vitamin D), disease resistance, dietary deficiencies (e.g. iron), Neanderthality. Individual genetic variant effects on personality traits such as gluttony are small in magnitude  compared to the genes affecting the life and death type phenotypes. In passing, very roughly, evolutionary psychology assumes the traits they are looking at went to fixation “in the Pleistocene”, and so will be species stereotypic, while behavior geneticists are interested in present and past genetic variation and individual difference.
I see the modern scientific models in this area (moral psychological, game theoretic, population genetic) as something like “the human package of trust, cooperation and morality maximizes persistence of a society on average.” It doesn’t say anything more than these particular behavioral codes are functional, not that they are necessarily genetic or cultural, right, good, lead to perfection of the individual or the species in the future. It is loosely Darwinian in form of argument, but doesn’t have to be evolutionary genetic in nature.
 Mayo O. (2018). Evolution by Natural Selection and Ethics: What in evolution has ethical implications? Borntrager, Stuttgart 2018. http://www.bontraeger-cramer.com/9783443500405.
 Brunetière F (1896). La Moralité de la Doctrine Évolutive.
 De Duve C, Patterson N (2010). Genetics of original sin: the impact of natural selection on the future of humanity. New Haven, CT: Yale University Press.
 Fisher R.A. (1923) The Eugenics Review 14: 190-193.
 Incidentally, not Christianity – “the progressive change of moral opinion among Pagan writers from Plato to the jurist Julius Paulus…cannot be easily ascribed to the state of Christian feeling upon the subject”.
 Thornhill R, Palmer CT (2000). A natural history of rape. Cambridge, MA: MIT Press
 Guyau JM (1885). Esquisse d’une morale sans obligation ni sanction. Ancienne Librairie Germer Bailliere.
 Spinoza B (1670). Tractatus theologico-politicus. Ch 16.
 Theofanopoulou C, Gastaldon S, O’Rourke T, Samuels BD, Messner A, Martins PT, et al. (2017). “Self-domestication in Homo sapiens: Insights from comparative genomics.” PLoS ONE 12(10): e0185306. https://doi.org/10.1371/journal.pone.0185306
 Persson ME, Sundman AS, Halldén LL, Trottier AJ, Jensen P. “Sociality genes are associated with human-directed social behaviour in golden and Labrador retriever dogs.” PeerJ. 2018 Nov 6;6:e5889. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6225837/
 For example, the FTO allele that increases body weight diminishes energy intake by 6 kcal per day, that is 1/4 teaspoon of sugar). See Qi Q, Kilpeläinen TO, Downer MK et al (2014). “FTO genetic variants, dietary intake and body mass index: insights from 177,330 individuals.” Hum Mol Genet. 23:6961-72.