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The (probably) majority view is the one most famously articulated by Richard Dawkins that selection acts on genes and that evolution can be said to occur when a particular gene becomes more prevalent in a population over time as a result of selection pressure. Pigliucci and Kaplan, amongst others, point out that selection most obviously happens at the level of individual organisms (it is the trait that is selected for directly) and that the phenotype (the set of physical characteristics) does not always map easily onto a particular gene. Pigliucci is also sympathetic to group selection theories where selection acts upon the fitness of populations rather than individuals or genes.
There is a certain, if limited, parallel here with religion. Practitioners of a particular religion will agree on the main premises; name of deity, lives of prophets, holy scriptures etc. but frequently display disagreement on finer points of theology and practice. Take the early Catholic Church’s struggle with the Trinity, or even the modern Anglican Church’s dilemma over the role of women in the hierarchy, both examples of a heterodoxy of opinion beneath the surface of a common orthodoxy.
The parallel breaks down however in the different ways science and religion deal with the issues. In the case of the Catholic Church, after convening a council of Bishops and establishing the Nicean Creed the Church then went on a mission to brand dissenters as heretics and literally kill off the opposition. The result over centuries was entrenchment of dogma and multiple schisms with, ultimately, many different sects following their own interpretations and although I don’t see the C of E branding anyone a heretic over women Bishops, I would not be surprised to see breakaway dioceses comprised of the disaffected.
Religion has no choice but to deal with dissent and disagreement in this way, either by enforcing a creed or disintegrating and factionalising. Why? Because there are no empirical facts to be discovered that can inform the arguments. Theological disputes have nothing to fall back on except their scriptures and their traditions both of which are open to interpretation without empirical data to support them
Science on the other hand does not have this problem. For sure, it develops its own orthodoxies and there are conservative elements that defend them and others that challenge them. True, arguments get heated and nasty and sometimes a faction forms and enmities emerge. But, ultimately all scientists know that at some point the argument will yield to hard facts and experimental data, knowledge and understanding will advance and paradigms may change
In the example about levels of selection above the ‘correct’ answer is not immediately clear. Evolution is a simple idea in principle but turns out to be very messy and difficult to quantify in practice, life being what it is and not easily reducible or predictable. My own intuition, for what it’s worth, is that no matter how complex the interaction between organisms and their environments proves to be the final answer will be found in the genome. Although this may be because I am a product of the W.D. Hamilton and Richard Dawkins generation of biologists who first expounded the gene-centric view of evolution. But Pigliucci, Kaplan and their ilk could easily be correct and as long as it isn’t completely intractable the truth will emerge in the observational and experimental data eventually.
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