One might quibble whether it is correct to describe essentialism as a scientific idea, but then again it's something you can still find kicking its way through popular cultural artefacts and continues informing ostensible scientific study. Dawkins takes essentialism to task as a fundamental category error, of confusing the concept that describes and object with the object itself. Hence in his example, all rabbits have a certain "rabbitness" inscribed into their furry, hoppy natures. Each individual rabbit embodies the essence of rabbit as described by the concept 'rabbit'. In such conceptual terms it is at best supremely difficult and distorting, and at worse completely useless to think about the evolution of species in this way. When did rabbits become rabbits? At what point in the fossil record did evolution convey on them the essentialness of rabbitry? As Dawkins rightly notes, the question is as dumb as it is pointless.
Of course, in sociology and politics we've had our own battles with essentialism. In social science and philosophy, with the odd exception, essentialism has long been routed from theoretical discourse. The coincident impacts of feminism, anti-racism/post-colonialism, queer theory, Althusserian Marxism condensed with the rise of postmodernism and the deconstructive impulse of post-structuralist philosophy has dropkicked Plato's legacy out of the ring. For the first time since August Comte penned his Course in Positivist Philosophy there is an unspoken consensus in social theory at large. There are still fierce disputes between rival perspectives that will never go away, but there is a core acceptance in post-postmodern social science around a very broad definition of history founded on the materiality of social dynamics/processes. Unconsciously Marxist is stretching it a bit, but the acceptance of the contradictory interconnectedness of things has sneaked into the default common sense. The economist Joan Robinson once observed you couldn't read Capital without Hegel's nose popping out. Likewise, you open a work of social theory today and you'll find a few unremarked upon wisps of Marx's beard.
Dawkins has from time-to-time embroiled himself in controversy over careless remarks. One might almost call it trolling. For example, this spot of controversy came about after tweeting comments that are a little bit essentialist and shade into the Islamophoic. And, of course, you don't need me to remind you that there are plenty about who read the behaviour of Muslims off from the more problematic passages of the Qu'ran. Always it's particularly pernicious understandings of the category 'Islam' each and every Muslim is held to be an appendage of. Alongside his unguarded stereotyping, I noted here yonks ago his atheism, and that promulgated by the so-called "new atheism" is, philosophically speaking, idealist. This is what was said then:
On the one level Dawkins accepts Wittgenstein’s famous dictum that “the world is all that is the case” but for him this remains a contemplative position. This might be enough to see him through his studies of genetics but an abstract nod to a godless world is unsuited for understanding the sensuous and active world in which we live. We cannot grasp the pull of religious ideas without simultaneously being aware of the real, historical existence of the people who adhere to them. It is not enough to suggest religion speaks to universal human concerns. That cannot begin to explain why, for example, the Palestinian militant is more likely to adopt fundamentalist Islam than the Orthodox Judaism of the Israeli settler. But also mundane everyday life is, for the overwhelming majority, profoundly alienating. Those who sell their labour power for a wage or a salary give themselves over to a power outside themselves for a set period of time, which shoe-horns them into a circumscribed role, directs their pace of work and then denies them access to the full fruits of their labour. When society is subordinated to the demands of a blind alien power, when people are atomised, individuated and powerless, the belief we are but feathers buffeted by a divine wind can make more sense than salvation lying in our own self-activity as beings capable of consciously making history.In other words, the critique of religion - if one is interested in such things - has to be approached as a social phenomena, as what good old Durkheim called a social fact. Unfortunately though Dawkins' contemplative position sets up an opposition, a rigid distinction between believers of whatever creed, and the godless. Being unbelieving is a matter of personal growth, of intellectual and mental maturity, of possessing reasonable and rational-critical faculties. One might observe that this idealist position lapses into essentialist thinking. It's not that all religious people are unintelligent, but clearly on some level they're all stupid, or so the assumption goes.
Regardless of what one thinks of Dawkins, whether one hangs on his every dot and comma or takes a more critical stance, his choice to dump essentialism is an interesting one as binning it means breaking with a component of his own philosophical atheism. Hopefully some fresh, more interesting thinking through of religion and atheism is just around the corner.