Alan doesn’t believe that there are any other proposed explanations to rival ‘evolutionary theory’. At least none that so effectively account for the facts.
It is often said that there is no single theory of evolution, there are a group of mutually consistent theories. Be that as it may, I think we all understand the point Alan is making.
Evolution is a process whereby life has somehow emerged from a lifeless physical world and there is no overall teleology involved in its diversification. The reproductive processes produce a natural variety of forms which can take advantage of previously unoccupied niches. The basic sequence of events from primal to present are: lifeless minerals, water systems and gaseous atmosphere, followed by the arrival of simple prokaryote life forms, followed by multicellular organisms. Life is solely the product of physical and chemical processes acting on lifeless matter.
In this view life is nothing special, it just occurred because physical matter chanced to arrange itself in a particular way. And consciousness is just a by product of life.
But I suggest that there is an alternative way in which life as we perceive it could have come about.
Arthur Zajonc in the book Catching the Light: The Entwined History of Light and Mind
Goethe was right. Try though we may to split light into fundamental atomic pieces, it remains whole to the end. Our very notion of what it means to be elementary is challenged. Until now we have equated smallest with most fundamental. Perhaps for light, at least, the most fundamental feature is not to be found in smallness, but rather in wholeness, its incorrigible capacity to be one and many, particle and wave, a single thing with the universe inside.
In the same way that in the above quote light is understood in its wholeness, so can life be understood as a whole. The variety of earthly life forms that have existed through time and space are individual expressions of an ever present archetypical whole. Life is one and many.
Holistic science attempts to get closer to the mystery of the dynamical emergence of the diversity of living forms within the unity of the continuously manifesting whole.
An arithmetical analogy between orthodox accounts of evolution and evolution as the unfolding expression of archetypal forms could be that the former is akin to addition while the latter is akin to division. Novel forms are an extra addition to what came before or novel forms are divided off from what already existed in potential. From the parts to the whole or from the whole to the parts. Which is it? Sense perception points to the former while the mind’s eye, perceiving with the mind, points to the latter. And Goethe was an expert at perceiving with the mind.
Instead of life emerging out of matter in an extended version of the spontaneous generation of mice from mud, it could at least be regarded as a possibility that physical organic life is a condensation or hardening of form out of a more subtle general condition which contained all physical forms in potential. This is analogous to crystals emerging out of solution. The perception of salt in sea water is dependent on the senses of the perceiver. Some forms of life have not descended as completely as others and thus retained more plasticity and because of this they are more adaptable to changes in their surroundings.
Life is and always was everywhere but it is only when it coalesces into gross material forms that it is perceptible to our everyday senses.
Convergent evolution is explicable not just by occupation of similar niches but by similar forms coalescing.