Jane Harris Zsovan posts on a blog called Design of Life. I don't read her blog on a regular basis but Denyse O'Leary recently linked to a post on how speciation doesn't agree with evolutionary theory [Hybridization One Key to Survival].Jane Harris Zsovan is intrigued by hybrids that appear to be more fit than either of their parents. She thinks this conflicts with Darwinian Theory. Here's an example of how she thinks evolution should work.
Hybrids With Genetic Advantages A Problem for Darwinian TheoryThere are many different ways for two isolated populations to evolve into separate species. In many (most?) cases the two lineages diverge by random genetic drift and not just natural selection. The exact mutations leading to genetic incompatibility are most likely to arise by accident and become fixed in one of the lineages by drift.
Darwin's theory of natural selection requires offspring to diverge from a common ancestor to create new species. It requires genetic differences to increase as descendants adapt to their environmental niches.
It is this 'natural selection' and 'adaptation' that creates species. And, as the newly created species continue to adapt, they should become more different over time. Following this line of thought, hybrids should be less viable than their parents.
Evolutionary theory does not require that two separated lineages diverge by natural selection. Speciation does not depend on adaptation. This hasn't been a requirement of speciation for over thirty years [Speciation].
Typically a new population will be founded by a small number of individuals. As the new isolated population grows it will lack much of the genetic variation of the parent population and, consequently, it may be far less fit in it's new environment than a random selection of individuals from the parent population might be. An infusion of new alleles from the parent population by hybridization might lead to individuals that are more fit.
There is nothing in evolutionary theory that says hybrids can't be more fit than either parent. The flaw in Jane Harris Zsovan's logic is entirely due to the obsession creationist have with Darwin and natural selection. They have convinced themselves that everything in evolution must be explained by "Darwinism." This fits with their political agenda. That's why they try so hard to associate evolution with a man who died over one hundred years ago.
The irony comes when they start believing their own false caricature of evolution. That's what happened here, and Denyse O'Leary falls for it hook line and sinker [ More evidence that Darwin's theory of natural selection as the origin of new species is wrong]. The title of Denyse's post is very revealing. Of course, it's wrong to attribute everything to natural selection. Denyse has been told this time and time again and so, I presume, has Jane Harris Zsovan. They are very slow learners. They look like IDiots.
"They are very slow learners."
ReplyDeleteIt's far too kind to describe ID-creationists who actively refuse to being taught as slow learners. One can not characterize the few occasions ID-creationists seem to have accepted reasonable arguments (like Behe with common descent) as learning because these are just tactical moves that are directly followed by building the next strawman.
This is a rather silly comment:
ReplyDeleteIn the case of the Darwin's finches, even the 'purebred' finch populations show little tendency to sustain changes in size or shape of their beaks over the long term. This scenario is exactly what Darwinian theory doesn't predict.
As Grant notes and she quotes, ""the population, selected to natural selection, is oscillating back and forth". The traits are oscilating with environmental changes. When it is wet, you get more variation, when it is dry, larger beaks are favoured. In other words, natural selection is operating! Which is precisely what "Darwinian theory" predicts. It doesn't predict that beak size should remain large in the absence of the selective pressure to do so.
Zsovan is also apparently not keeping in touch with the literature. Presumably because she gets most of her information from Icons of Evolution which is a) quite a few years old and b) a load of crap. In their 2006 paper, the Grants present further evidence for selection in action, as a result of the arrival of a competitor for G. fortis (which results in smaller beak sizes). If she is even aware of this research, she probably has avoided mentioning it because as the Grants note, "this is the strongest evolutionary change seen in the 33 years of the study."
Grant, P.R. and Grant, B.R. (2006) Evolution of Character Displacement in Darwin's Finches. Science, 313, 224-226.
I think what really bothers Zsovan is that biology is messy. Things are rarely neat and simple to package (and sell to your supporters). The real world tends to be rather more complex and I think this disturbs her. The Grants, of course, are aware of this and provide a neat summary of the complexity of the situation:
The barrier to gene exchange in sympatry is not completely effective, however: species hybridize rarely, and under some circumstances the hybrids are surprisingly fit. These results challenge some current notions of species. For example, the ground finch species Geospiza scandens Gould and G. fortis Gould on the island of Daphne Major have lost morphological diagnosability, as a result of introgressive hybridization, while retaining vocal diagnosability. Speciation is a process of divergence, and therefore these two populations are currently despeciating. With a change in climatic conditions they are expected to respeciate. Such merge-and-diverge dynamics may occur frequently in hybrid zones and in relatively Young radiations in habitats subject to strong environmental fluctuations.
Grant, P.R. and Grant, B.R. (2006) Species before speciation is complete. Annals of the Missouri Botanical Garden, 93, 94-102.
The Grants have a paper that looks in some detail about hybridization. For some reason she doesn't mention the results of this research. I'll pick out a couple of quotes that may well illustrate why:
Our study is most relevant to speciation and the potential for new directions of evolution (Grant and Grant 1994). For example, G. fortis and G. scandens have different allometries, and when introgressive hybridization occurs the allometries are genetically altered through a reduction in strength of genetic correlations between traits. With enhanced genetic variation but reduced genetic constraints, the two populations have the potential to evolve in new directions more easily than in the absence of introgression (Grant and Grant 1994).
and
introgressive hybridization results in novel gene combinations being formed (Stebbins 1959; Sva¨rdson 1970; Mecham 1975), and these create the potential for niche, habitat, or range expansion if environmental circumstances are favorable (Lewontin and Birch 1966; Chiba 1993; Pierotti and Annett 1993; Grant and Grant 1994; Arnold 1997; Rieseberg et al. 2003a,b; Smith et al. 2003). This is a possible route to speciation (Sva¨rdson 1970; Salzburger et al. 2002; Rieseberg et al. 2003b).
Grant, P.R. et al. (2004) Convergent evolution of Darwin's finches caused by introgressive hybridization and selection. Evolution, 58, 1588-1599.
Finally, as a further illustration of her non-existent logic, Zsovan waffles about hybrids, ending up with this statement by arguing that hybrids should be less viable than their parents and provides a few examples of where they are more fit. This, somehow, argues against "Darwinian theory". However, given that there are loads of examples where hybrids are less fit. I therefore assume that in the near future we will be seeing Zsovan write these up as stunningly examples of the success of Darwinian predictions.
One related thing I recently wondered about is how the larger speciation mutations (like duplication of whole chromosomes like with donkeys vs horses and that lead to sterility when mating with the "original" genome) do actually happen originally.
ReplyDeleteWouldn't they require that at least two individuals have the same mutation independently and that they
mate?
Hmmm, my final paragraph is stunningly badly written. Hopefully the point still comes across.
ReplyDeleteAll very plausible and as an evolutionist I'm inclined to believe it. Excuse my ignorance, but inspite of the assured, assertive and authoritative tone I would like to know what observations in the fossil record and the genes actually support this view? Or is it just a theoretically sound construction that seems to work?
ReplyDeleteWhen I'm over on Uncommon descent, they won't buy it if I just say, "Well, Larry said so!"
Re the question from anonymous:
ReplyDeleteTwo animals with the same genetic change aren't required to mate for speciation to take place. Do more reading on topics like genetic drift, neutral theory, and biogeography (an IMO wonderful book on this last topic for a general readership is David Quammen's "Song of the Dodo").
Even if one looks exclusively at natural selection, think about phenotype (morphological expression) vs. genotype (genetic makeup). There's no requirement that both parents share a genetic trait in order for it to show up in the phenotype of the offspring (which, more generally speaking, ISTM shows this whole "hybrids are less fit" line of argument for the nonsense it is).
When I'm over on Uncommon descent, they won't buy it if I just say, "Well, Larry said so!"
ReplyDeleteYeah, only the most rigorous standards of evidence are sufficient to convince them!
Larry, there is some debate in the literature about the role of natural selection in speciation. In speciation with some gene flow (sympatric or parapatric), there most likely needs to be selection to drive speciation between two demes. However, when it comes to allopatric speciation, the role of selection isn't quite as clear. Coyne and Orr argue in their book (the best collection of information on speciation in sexually reproducing taxa) that natural selection is required for the evolution of reproductive isolation between allopatric demes. This is based on laboratory experiments in which reproductive isolation is evolved through selection for two different habitats. In allopatry, selection isn't for reproductive isolation, per se, but it is often a byproduct of different selection regimes in different habitats. I don't doubt that reproductive isolation will eventually evolve in allopatry, however I think divergent selection in the two demes accelerates the process.
ReplyDeleteOne related thing I recently wondered about is how the larger speciation mutations (like duplication of whole chromosomes like with donkeys vs horses and that lead to sterility when mating with the "original" genome) do actually happen originally.
ReplyDeleteThe topic of karyotypic speciation is quite interesting, but I think you have your facts wrong. Horses and donkeys don't differ by a duplicated chromosome. If they have different karyotypes, it's the result of a chromosomal fusion or fission resulting in different numbers of chromosomes (similar to what happened after humans and chimps diverged).
While these gross karyotypic changes may incur fitness costs in the form of reproductive barriers with other individuals (or decreased survivability of the individual harboring the genomic rearrangement), they are often only mildly deleterious or neutral. Individuals with slightly different karyotypes from the same population can often mate perfectly fine with each other. There are some data (both empirical and theoretical) that suggests that the chromosomal rearrangements harbor alleles that act as reproductive barriers between karyotypes, rather than the rearrangements being barriers themselves. These reproductive isolating genes are preferentially located in chromosomal rearrangements because suppressed recombination between karyotypes prevents their introgression from one chromosomal arrangement to another.
P.S. Sorry for the jargon. If any of the terms are unfamiliar, it's a good learning experience to look them up.
Larry,
ReplyDeleteAs you know this post has irritated me since it was posted. As you know, Denyse and I belonged to the same writers' organizations and she offered me work when I needed it. However, I thought you might be interested in reading what I have say in this post on my own blog."Listening (for a change)to the other side."If your readers want to know who I am and what I write, I suggest they go to my blogs or check out my Writers' Union of Canada and Writers' Guild of Alberta bios, Cheers, Jane Harris-Zsovan, Author, Eugenics and the Firewall: Canada's Nasty Little Secret (J. Gordon Shillingford, 2010) and Stars Appearing: the Galts' Vision of Canada (2006): http://visionofcanada.blogspot.com/