Here’s an interesting food for thought in regards to the origin & evolution of plants and how they became so diverse.
One of the common arguments evolutionists use to support the claim that evolution can create new novelty/new genetic information is polyploidy. Polyploidy, also known as genome doubling, is the process where a living organism acquires one or more additional set of chromosomes.
Conceived from the early 1900s down to the present, polyploidy has been viewed as one of the major forces that contributed to the evolution of new species, new genera, etc. However, polyploidy is considered to be rare among animals in general, but very common among the plant kingdom. Due to the extreme rarity of polyploid from animals in general, evolutionists believe that the major diversification and macro-evolutionary changes of plants have been mostly associated with genomic doubling/chromosome duplication.
As the pro-evolution site, Talk Origins, states in their +29 Evidences For Macroevolution:
Special paradiumerous plants, both angiosperms and ferns (such as hemp nettle, primrose, radish and cabbage, and various fern species) has been seen via hybridization and polyploidization since the early 20th century.
Yet, one of the greatest and influential botanist and geneticist evolutionary figures, G. Ledyard Stebbins, has created harsh scientific criticism against the assumption that polyploidy is able to create novelty or large-scale morphological features, as required by the neo-Darwinian paradigm. Here are some of his arguments:
The classical paradigm of Polyploidy:
Polyploids as “dead-ends”: Limited importance in diversification
“Stebbins (1950 , 1971 ), as well as another highly influential plant biologist of the 1900s, W. “Herb” Wagner, argued that while polyploids were frequent in plants, they had limited long-term evolutionary potential. This traditional view that both strongly promoted maintained that polyploids were “evolutionary noise” ( Wagner, 1970 , p. 146) unimportant to the main processes of evolution (e.g., Stebbins, 1950 ; Wagner, 1970 ). For Stebbins and other students of polyploidy from that time period, the evolutionary action was at the diploid, not the polyploid, level. For example, Stebbins (1950 , p. 358) stated, “Polyploidy, therefore, may be looked upon as a process which is most effective as a means of enabling species groups which have reached a certain stage of depletion of their biotypes…to adapt themselves to new environmental conditions which arrive relatively suddenly. It is much less important in stable environments and in diploid species which are still widespread and rich in ecotypic differentiation.” Stebbins (1950 , p. 359) further noted, “The long-continued evolution needed to differentiate genera, families and orders, and phyla appears to have taken place chiefly on the diploid level…” Stebbins (1950 , p. 366) later states “… polyploidy has appeared as a complicating force producing innumerable variations on old themes but not originating any major new departures.”
To rephrase it seems that polyploidy, the doubling or duplication of chromosomes which is believed by evolutionists to be a major driving evolutionary force of novelty or new morphological features, has serious limitations. The most gravest problem with polyploidy according to Stebbins is that it is essentially an evolutionary dead-end, as it does not lead to the evolution of new genera, families, nor orders. The best polyploid can acheive is simply produce new species with innumerable variations of already pre-existing traits, but nevertheless lacks the ability to produce new major morphological innovation/macro-evolutionary changes.
Furthermore, the creation of lower to higher taxa (i.e. from genera to orders/families) have been found to be present only at the diploid level, meaning that they were derived from species with normal chromosome counting obtained by their parents as opposed to the addition of new chromosomes.
In addition to the limitation:
“Recent reanalyses of data for ferns and angiosperms revived the concept of polyploids as evolutionary dead-ends, indeed using this very word ( Mayrose et al., 2011 ; see also Arrigo and Barker, 2012 ). Mayrose et al. (2011) argued that polyploids have higher extinction rates than diploids and are therefore often “dead-ends” that do not leave a legacy.”
It seems that species that undergo polyploidy, the addition of new chromosomes, are often associated with higher mortality rates: including deadly genetic diseases, infertility, etc. Essentially, polyploidy is for evolution an evolutionary dead-end, as it leads to the route of extinction rather than survival.
but wait, there’s more:
“A question of great interest is: Can populations of independent origin interbreed, or do they represent reproductively isolated lineages? Experimental demonstration of such interbreeding among polyploid lineages of separate origin is still rare. Recent work on Mimulus indicates that polyploid populations of separate origin are interfertile ( Sweigart et al., 2008 ). A mixture of results is apparent for populations of Tragopogon polyploids of separate origin; some populations appear to be interfertile, whereas some combinations are sterile”
According to Stebbins and thinkers like him, not only are polyploid speciation events associated with just evolutionary dead-ends, but they are also found to be so commonly infertile that successful reproduction would be considered a rarity among polyploid living organisms.
Summing everything up: it seems that polyploidy can no longer can be conceived as a major evolutionary force for the creation of new genera, families, & orders. The addition of new chromosomes is rather a counter-productive route for the modern synthesis of evolution, as it leads to the route of extinction and infertility. This brings biologists back to square one, where do all the new biological novelties come from if polyploid is not the mechanism?
Evolutionists to the rescue:
Despite the harsh criticism used against the neo-Darwinian model of polyploidy able to generate novelty or macro-evolutionary changes, some evolutionists wanted to put up a fight, something which they named the revolution and new paradigm of polyploidy.
The paper, published in the American Journal of Botany:
The polyploidy revolution then…and now: Stebbins revisited”
Here Soltis, an evolutionist in favor of the neo-Darwinian synthesis, has argued that polyploidy is not an evolutionary dead-end and that it is able to cause macro-evolutionary events. This was clearly going against what classics like Stebbins stated about polyploidy.
What was his line of defense?
The identification of ancient WGD events at many points in angiosperm phylogeny provides the opportunity to assess the correspondence between inferred genome duplication events and major diversifications—the role of polyploidy in “macrodiversification.” Many ancient WGDs are associated with key diversification events in angiosperm evolution, such as the origins of angiosperms, eudicots, and monocots. Examination of polyploidy events in Brassicaceae, Poaceae, and Solanaceae suggests that ancient WGD was followed by a burst in species richness, typically a few nodes after the WGD (Soltis et al., 2009).
The reasoning behind the logic goes like this:
“We think we see an ancient polyploidy event in this genome, therefore its novel traits must be due to the polyploidy mechanism.”
To rephrase,
“since we can’t find any evidence of novelty or macro-evolutionary changes occurring in present polyploids, we can go back looking to the past and point out that ancient polyploid/whole genome duplication events were the cause of such large-scale morphological and novel changes.”
So what evidence do they present to defend polyploidy? Ancient polyploidy/WGD events. Rather than demonstrating macro-evolution in the present and in action, they presumed that it must have been the case in ancient whole genome duplication events that occurred many million years ago.
The problem with this logic though is that it commits the fallacy of Post hoc ergo propter hoc (after this, therefore because of this)
The logic relies on the presumption that ancient polyploidy/whole genome duplication events were the cause of such novel body-plans. However, that reasoning itself is insufficient and fallacious, given that correlation is not evidence for causality.
Soltis matter is nothing more but mere speculation and wishful thinking. The idea that ancient polyploidy/whole genome duplication events have shaped the biodiversity observed in plants is also not free of problems. Quite the contrary, the whole ancient WGD hypothesis is brought with controversy in the scientific community rather than remain as a scientific consensus:
As stated in this 2014 paper:
Here researchers examined a recent whole gene duplication event named the salmonid-specific 4th WGD; otherwise abbreviated as Ss4R that has been dated 25 to 100 mya, Due to the recent Ss4R arrival, researchers had the opportunity to better understand the early steps of gene fractionation. They performed an analysis on the whole-genome sequence of the rainbow trout.
By examining the Ss4R regions, they discovered that most of the duplicated regions have revealed a surprising discovery: they found that nearly all of the duplicated regions have remained highly conserved and hardly diverged for 100 million years after the Ss4R event. Furthermore, they found that despite 100 million years of evolution after the Ss4r whole genome duplication event, they found that the ancestral gene and gene copies of it have extreme stability, emphasizing that the duplicated regions have remained remarkably well conserved in sequence identity and gene order on chromosomes. Which demonstrates interesting crucial points against the whole genome duplication hypothesis.
Problem with Ancient Whole Genome Duplication Hypothesis:
1) WGD does not involve many genomic rearrangements such as inversions or translocations that would otherwise modify the order of genes in the genome
2) It hardly involves deletions and neo-functionalizations
&
3) Pseudogenization is more common than producing functional genes. Even among pseudogenes caused by failed gene duplications, they remained highly strongly conserved across the entire genome
This is quite contrary to what the scientists in the paper argued, that body-plan morphogensis can be explained by whole genome duplication given that they involve large-scale genomic rearrangements, deleterious mutations, and neo-functionalization.
Rather, what this study reveals is that the rate of deletion, rearrangments, inactivation etc. is extremely tiny. It is in fact so slow that even after 100 million years after the Ss4R WGD event, there hardly ever remains any evidence of significant divergence in the entire genome. Given that Whole Genome Duplication involves more failures rather than success, this brings Soltis claim that ancient polyploid/WGD events drive the evolution of new body-plans into question.
As the researchers from the paper conclude:
“Here we show that after 100 million years of evolution the two ancestral subgenomes have remained extremely collinear, despite the loss of half of the duplicated protein-coding genes, mostly through pseudogenization. In striking contrast is the fate of miRNA genes that have almost all been retained as duplicated copies. The slow and stepwise rediploidization process characterized here CHALLENGES the current hypothesis that WGD is followed by massive and rapid genomic reorganizations and gene deletions.”
It seems that even after a considerable amount of time for whole genome duplicaiton to occur, there still hardly remains any evidence of divergence in the genome. This says a lot, since it shows that novelty by genome duplication is extremely rare, even in a 100 million year time scale.
Ironically, Soltis and his colleagues admit that:
Despite great progress in documenting the genomic and transcriptomic changes in polyploids relative to their diploid parents, we know little about the impact of WGD on the proteome (e.g., Albertin et al., 2006, 2007;Gancel et al., 2006; Carpentier et al., 2011;Hu et al., 2011, 2013; Kong et al., 2011;Koh et al., 2012; Ng et al., 2012). Given that the functional states of proteins in a proteome directly affect molecular and biochemical events in cells that determine phenotype, investigating how changes in gene expression profiles and AS events relate to protein-level changes is essential for understanding the molecular and evolutionary consequences of polyploidy, including molecular, biochemical, and physiological mechanisms that ultimately result in evolutionary change. Despite only a handful of proteomic studies of polyploids and their parents, some have revealed that the proteome of the polyploid does not always match the results predicted from the transcriptome alone; furthermore, novel proteins not found in either parent may be produced.
Judging by their overall conclusion, it seems like they admit that their understanding of what WGD events can achieve is very unclear, as they do not know for certain whether such can generate novel complexities. To them, there only remains the expression of hope and dreams that one day with enough research they will finally be able to find the smoking gun mechanism involving novel/macro-evolutionary changes.
Perhaps the reason why biologists can’t find any such mechanism that leads to macro-evolutionary changes is because probably there was never such thing. Instead, all the biodiversity present could be explained that perhaps biological life was seeded rather than evolved from one form to the other.
They have yet to provide a feasible mechanism that can explain how life became so diversified from one different taxonomy to the other.
Nevertheless, that has yet to be seen.
angeldiaz. 