NOTE: 'Free will' in this question describes an ability to have chosen otherwise, given the same circumstances.
According to American Scientist, Darwin came to a belief that we had no free will 30 years prior to his publishing The Variation of Animals and Plants Under Domestication (roughly 20 years prior to Origin of the Species). He stated:
"The general delusion of free will is obvious because man has power of action, & he can seldom analyse his motives (originally mostly INSTINCTIVE, & therefore now great effort of reason to discover them…)".
Anthony Cashmore, Doctor of Biology, Pennsylvania State University, explains his exploration of the notion of a genetic basis for consciousness and the associated belief in free will. Free Will is an Illusion, Biologist Says.
Consciousness has an evolutionary selective advantage: it provides us with the illusion of responsibility, which is beneficial for society, if not for individuals as well. In this sense, consciousness is our "preview function" that comforts us into thinking that we are in control of what we will (or at least may) do ahead of time. As Cashmore notes, the irony is that the very existence of these "free will genes" is predicated on their ability to con us into believing in free will and responsibility. However, in reality, all behavioural decisions are nothing more than a reflection of our genetic and environmental history.
"Whereas the impressions are that we are making 'free' conscious decisions, the reality is that consciousness is simply a state of awareness that reflects the input signals, and these are an unavoidable consequence of GES [genes, environment, and stochasticism]," Cashmore explained.
To summarize, Cashmore's argument is that free will is an illusion derived from consciousness, but consciousness has an evolutionary advantage of conferring the illusion of responsibility.
In The Atlantic, Philosopher Bruce Waller, Philosopher Professor at Youngstown, presents a different, compatibilistic view.
For Waller, it simply doesn’t matter that these processes are underpinned by a causal chain of firing neurons. In his view, free will and determinism are not the opposites they are often taken to be; they simply describe our behaviour at different levels.
Waller believes his account fits with a scientific understanding of how we evolved: Foraging animals—humans, but also mice, or bears, or crows—need to be able to generate options for themselves and make decisions in a complex and changing environment. Humans, with our massive brains, are much better at thinking up and weighing options than other animals are. Our range of options is much wider, and we are, in a meaningful way, freer as a result.
Bjorn Brembs, Professor at Universität Regensburg in Germany, (perhaps ambitiously) claims that with his article, "Towards a scientific concept of free will as a biological trait: spontaneous actions and decision-making in invertebrates" he has, "...argued successfully that we would not exist if our brains were not able to make a different choice even in the face of identical circumstances and history".
The explanatory power of evolutionary biology is considerable, but - ignoring other disciplines as much as possible for the moment - which of its principles and/or concepts might be employed in an attempt to discern whether the free will with which it has imbued us is illusory or accurate?
NOTE: This post may be deemed to insufficiently straddle the realms of science and philosophy; that it may be best asked in a separate stack. I have posted it here in the hope it contributes to a local accumulation of material relevant to the question of free will, and that whilst it focuses upon scientific enquiry, it poses a question which does not - according to a cursory review - appear to be adequately/conclusively answered by the literature. I hope it provokes a speculative discussion of biological principles which might fairly be considered "philosophy of biology". The Internet Encyclopedia of Philosophy defines 'philosophy of biology' as:
"Philosophy of biology is the branch of philosophy of science that deals with biological knowledge. It can be practiced not only by philosophers, but also by scientists who reflect on their own work.