Tag: University of Michigan

The Theory of Evolution propounded by Charles Darwin,I have been arguing through my posts is one of conjectures and not conclusively proven.

I have posted a couple of blogs on this,

One of the pillars of the Theory of Evolution is Dollo’s Law,

” “An organism is unable to return, even partially, to a previous stage already realized in the ranks of itsancestors.”^[2] According to this hypothesis a structure or organ that has been lost or discarded through the process of evolution will not reappear in exactly the same form in that line of organisms.^[3][4] According to Richard Dawkins, the law is “really just a statement about the statistical improbability of following exactly the same evolutionary trajectory twice (or, indeed, any particular trajectory), in either direction.”^[5] Stephen Gould viewed the idea less strictly, suggesting that “irreversibility” forecloses certain evolutionary pathways once broad forms have emerged: “[For example], once you adopt the ordinary body plan of a reptile, hundreds of options are forever closed, and future possibilities must unfold within the limits of inherited design”

But a  Field Study in the field disproves this.

“In evolutionary biology, the notion of irreversibility is known as Dollo’s Law after the Belgian paleontologist that first hypothesized it in 1893. He stated that once a lineage had lost or modified organs or structures, that they couldn’t turn back the clock and un-evolve those changes. Or, as he put it, “an organism is unable to return, even partially, to a previous stage already realized in the ranks of its ancestors.”

While some animals seem to challenge Dollo’s Law, it has long been a deeply held belief in the field of parasitology. Parasitism is, in general, a process of reduction. Adjusting to survival on or in another animal is a severe evolutionary undertaking, and many parasites lose entire organs or even body systems, becoming entirely dependent on their hosts to perform biological tasks like breaking down food or locomotion. Parasitology textbooks often talk about the irreversibility of becoming a parasite in very finite terms. “Parasites as a whole are worthy examples of the inexorable march of evolution into blind alleys” says Noble & Noble’s 1976 Parasitology: the Biology of Animal Parasites. Robert Poulin is even more direct: “Once they are dependent on the host there is no going back. In other words, early specialisation for a parasitic life commits a lineage forever.”

Now, parasites are proving that not only can they evade immune systems, trick other animals, and use their hosts’ bodies in hundreds of nefarious ways, some can go back to living on their own. This is exactly what scientists now believed happened in the Pyroglyphidae — the dust mites.

Mites, as a whole, are a frighteningly successful if often overlooked group of organisms. More than 48,000 species have been described. These minuscule relatives of spiders can be found worldwide in just about every habitat you can imagine. Many are free-living, but there are also a number of parasitic species, including all-too-familiar pests like Sarcoptes scabiei, the mite which causes scabies. Exactly how the different groups of mites are related to each other, however, has been a hot topic of debate amongst mite biologists. Though the closest relatives of dust mites are the Psoroptidia, a large and diverse parasitic group of mites, many have argued that dust mites came from free-living ancestors — ‘living fossils’ of a sort, the only surviving line of ancestral free-living mites that later gave rise to parasites. In fact, Pavel Klimov and Barry O’Connor from the University of Michigan were able to find 62 different hypothesis as to how the free-living the dust mites fit into the mite family tree. Sixty-two, the team decided, was simply too many. So, they turned to the mites’ genes.

To test which of the hypotheses had the most merit, Klimov and O’Conner conscripted a team of 64 biologists in 19 countries to obtain over 700 mite specimens, which they then used to construct a mite family tree. They sequenced five nuclear genes from each species, then applied statistical analyses to construct a tree of relationships called a phylogeny. And that’s when they saw it: deeply nested inside a large group of parasites were our everyday, non-parasitic, allergy-causing dust mites.”While this isn’t the first time that Dollo’s Law has been questioned, it’s the first strong evidence that parasitism might not be the evolutionary “blind alley” we tend to describe it as. The more scientists use genetics to study the evolutionary relationships between organisms, the more they find that Dollo’s Law is less law-like than once thought, broadening our understanding of evolution as a whole and challenging our assumptions about how it works. Which is, really, the brilliance and beauty of science — like life on this Earth, our understanding of the universe is constantly adapting and evolving.

…

http://blogs.discovermagazine.com/science-sushi/?p=2641#.UULq_xeLCXd

Related articles

• House Dust Mite Study Shows Reverse Evolution Possible (natureworldnews.com)