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.
Someone ( I think it was Schizophora) posted before about six-winged insects in the Carboniferous. Maybe that was the ancestral form; a pair of wings and legs on each thoracic segment.
ETA
Looks like a fairly distant relative of fruit flies to me. More like a cross between a dragon fly and a mayfly.
But a very interesting specimen none the less.
It was a joke; a bit of wry levity, adopting the gamete’s eye view of proceedings.
Those are rather loaded terms you are using there. Could we stick to recombination and mutation, please? Also, “speculating” is not the most accurate description of how scientists work.
To answer your question: mutation introduces novel variants at a given genomic locus, whereas recombination in general does not. Since most lineages have diverged at many loci, without having exhausted their standing variation, it follows that this process is fueled by mutation, not recombination.
Divergence of lineages by recombination only is pretty hard to achieve. You need strong selection to get divergent phenotypes and the resultant lineages will be highly inbred since you need to fix the novel allele combinations in place. The whole thing wouldn’t get very far without mutation refueling the standing variation.
Ancestral?
I remembered this bit of trivia from my time as a drosophilist, but I verified on Flybase that there indeed exist spontaneous mutants of Ubx, e.g. this one. I believe it was Calvin Bridges that described the first bithorax mutant. The crumbs of this history can be seen in the text you quoted: “[…] in the early years when the mutant transformations were quite incomplete […]”. It is true that these early mutants did not look like the pretty “dragonflies” in the pictures you posted, but they did have enlarged flattened halteres bearing the characteristic wing margin bristles. That was enough to make these early investigators realize that the halteres had developed as wing-like structures.
Unfortunately, nobody but you seems to be able to do so.
Perhaps you should prefer the definition that other people are using. It helps communication.
From my point of view you are constantly making stuff up.
Have mercy, Charlie. Please try to see things our way a bit.
Alan is right: You are recognizing the ancestral characters. Mayflies have preserved the tails and dragon flies kept the double pairs of large wings. Both have preserved the inability to fold their wings flat.
When dealing with the evolutionary past, sometimes speculation is all they have.
That does not answer the question I asked. The appearance of novel forms during evolution is assumed to be achieved in large part by accidental changes to the genome, accidental mutations. The causal direction is always assumed to be from the part to the whole, or from an external source.
A causal direction from the whole to the parts allows for purposeful changes in form. And if you believe that nothing like that exists in nature, then look at human activities. To take an extreme example, if a person commits suicide it is not their genome or any individual cells that are telling them to do it, it is the person, the whole being that decides on its own organisational fate. A less extreme example would be Alan shaving his beard off. The change in form was instigated from ‘above’ not ‘below’.
Yes, but what I mean is that I can see mayflies or dragonflies being the direct descendants of this organism, but not fruit flies.
I know that nature produces abnormal fruit flies, and so I was asking if there are any instances of four-winged flies spontaneously appearing. Fly with wings like those produced by Edward Lewis. As far as I know he had to combine three mutations to achieve this result.
Yes there are various fruit fly mutants in existence. But as far as I know there are none that just happen to produce anything like an extra pair of functional wings.
To stress a point about plants, Goethe said, “all is leaf”, meaning that stem, sepals, petals, stigmas and the rest can be thought of as transformed leaves. In agreement with Goethe I will say that in the fruit fly all is wing. Through the working of polarity and a series of expansions and contractions a wing can be transformed into a haltere and a haltere into a wing. They are the same thing expressed in an individual way.
And can you speak for every single person that studies these things?
All very good but it still avoids the question as to whether there exists any spontaneously mutated, viable, four-winged fruit flies like you implied.
Just one or two examples of convergent evolution from an endless supply:
Primates – Convergence in primate dentition:
Afradapis and Darwinius and human dentition are very similar but these primates are thought to be ancestors of lemurs and lorises. This dental similarity has been attributed to convergent evolution.
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Echolocation – convergence in bats and cetaceans and even between bat species.
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Cats – One convergent detail is that the fossa has retractable claws as do cats in general.
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Mammals – Obvious example convergences between various placentals and marsupials.
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Toads – Eyes with vertical-slit pupils have evolved separately in two families of fossorial toads, the rhinophrynid burrowing toads and the spadefoot toads. Not to mention this feature in animals that are far more distantly related.
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Roses – A comparison of roses with strawberries, show that these two members of the rosaceae family have evolved different enzymes to produce linalool {a fragrance chemical}.
The biosynthesis of phenylpropenies which participate in plant aromas. Rose stamens emit eugenol. The production of eugenol involves distinct pathways in different plants.
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I could go on indefinitely but I’ve run out of time. I was going to add something on Batesian mimicry. The striking resemblance between some butterfly species is proving difficult to explain in terms of Batesian mimicry. Maybe another time.
CharlieM,
I do not have opportunity to respond your comments, and will be gone for a while. See you in a week or so.
Hope you’re able to enjoy your break 🙂