I see that the question of the truth-status of the theory of evolution of all forms of life by natural selection is coming around again; as it does every few years and will continue to do until the matter is properly understood.
Because there is an answer, and it is quite straightforward: the theory that all forms of life on earth (all 'species') evolved exclusively by natural selection is a metaphysical assumption; not a scientific theory.
This is the plain truth of the matter - although to appreciate the fact requires that you understand the distinction (which is perfectly objective) between a metaphysical assumption and a scientific theory.
It also requires that you understand the distinction between the observable fact that humans (as well as other species) have 'traits' that evolve by natural selection (such as height, personality, strength); and the metaphysical assumption that this mechanism is the sole factor responsible for the many different forms of life on earth (past, present and future).
I have written on this subject in the past - and published an online mini-book (10,000 words) for the interested 'lay' reader called The Christian Evolutionist some five years ago. A deeper consideration was published in 2016 as a 10,000 word essay aimed at professional biologists.
Note: Anyone seriously wanting to engage with either or both of these pieces, is recommended to print-out paper copies - especially of the academic essay; because they are too long and complex to read on screen.
I don't think any scientifically literate person would venture to say that natural selection is the SOLE factor in evolution, just that it is the most important one and should therefore be the default assumption when it comes to explaining any particular biological phenomenon.
@William - In practice, the only allowable directional factor is natural selection; random, undirected factors - like genetic drift, or natural disasters, are allowed but do not lead to adaptation.
What other mechanism were you thinking of?
I was thinking of genetic drift and such. There's also artificial selection and sexual selection, but those can probably be considered special cases of natural selection. Artificial mutation (genetic engineering) is also a possibility in theory, but of course it is ignored in practice.
@William - The main debate in the time I was active (from about 1994-2016) was related to the balance between natural selection (including sexual selection) which increase fitness; and 'random' causes such as those you mention which are not linked to fitness.
A small sideshow related to the strength and significance (and definition) of group selection - which I talked about in the 'metaphysics' essay.
The real weirdness of natural-selection-as-metaphysics starts when one tries to take the next logical step and use it as theology e.g. extracting practical moral lessons, reinterpreting primary desires as evolutionary imperatives, asking "what would Gnon do" etc.
@Seijio - Indeed.
In practice any ideology based on Natural Selection is just a variant within the spectrum of mainstream Leftist utilitarianism...
Just with a different group whose utility is supposedly being optimised (i.e. 'my' extended family/ 'my' reproductive fitness), and a different definition of utility (i.e. the assertion that that genetic fitness - and not this-worldly, organism-derived pleasure/ absence of suffering - is the *real* utility).
I'm just now reading your essay, The Christian Evolutionist, which, by synchronicity, has come across my path at exactly the moment when I happen to be somewhat prepared to appreciate it. While reading it I had the following thought:
Regarding Macro-evolution vs. Micro-evolution
Could it be that macro is possible at a “low” level but not at “higher” ones? That a simple organism – a prokaryote, say – is capable of morphing in various directions but once more complex morphologies are established its phenotype will tend to become increasingly “stove-piped.” Macro would then be only possible up to a fairly early point after which all variation will increasingly be micro, focused on honing existing body plans.
This assumes that any evolution at all can happen only within the constraints allowed by pre-biotic chemistry or other more fundamental structures.
@Avro - Somewhat-against that is the 'standard view' I absorbed which was that the single most difficult steps in the history of life on earth were the earliest - the evolution of prokaryotic, then eukaryotic cells - particularly the step from p to e which seemed to take longer than any other stpe (once complex cells with choloroplasts, centrioles, mitochondria etc were available, it was just a matter of various modifications and combinations).
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