Posted on 11/27/2005 7:11:52 AM PST by Pharmboy
Species evolve at very different rates, and the evolutionary line that produced humans seems to be among the slowest. The result, according to a new study by scientists at the European Molecular Biology Laboratory [EMBL], is that our species has retained characteristics of a very ancient ancestor that have been lost in more quickly-evolving animals. This overturns a commonly-held view of the nature of genes in the first animals. The work appears in the current issue of the journal Science.
Detlev Arendt (left), Florian Raible and Peer Bork.
(Photo Credit: Marietta Schupp, Photolab, EMBL
Heidelberg)
Genes hold the recipes for proteins. The genes of animals usually contain extra bits of DNA sequence, called introns information which has to be removed as cells create new molecules. The number of introns in genes, however, varies greatly among animals. While humans have many introns in their genes, common animal models such as flies have fewer. From an evolutionary perspective, it was long assumed that the simpler fly genes would be more ancient. The current study reveals the opposite: early animals already had a lot of introns, and quickly-evolving species like insects have lost most of them.
To discover what early animals were like, scientists usually compare their descendents. This is difficult when comparing distantly-related animals such as humans and flies. In these cases, it helps to look at living organisms that have preserved many features of their ancestors. Detlev Arendt's group is doing this with a small marine worm called Platynereis dumerlii. "Similar animals are already found in the earliest fossils from the Cambrium, about 600 million years ago," Arendt explains, "arguing that Platynereis could be something like a 'living fossil'." This makes it an ideal model for evolutionary comparisons to find out what the common ancestors of humans, flies and worms were like."
Until quite recently, such comparisons could only be made by looking at physical characteristics such as the structure of bones, teeth, or tissues. But DNA sequencing now permits scientists to make comparisons of the genetic code and read evolutionary history from it. An international consortium involving researchers from EMBL, the UK, France and the United States has now sequenced a part of the Platynereis genome. "The fraction of Platynereis genes we have been able to look at tells a very clear story," says researcher Florian Raible, who performed most of the computer analyses. "The worms genes are very similar to human genes. That's a much different picture than we've seen from the quickly-evolving species that have been studied so far."
Raible is member of both Arendt's group and a second EMBL lab, that of Peer Bork, whose specialty is analyzing genomes by computer. "Human genes are typically more complex than those of flies," explains Bork. "Classicallystudied species like flies have far fewer introns, so many scientists have believed that genes have become more complex over the course of evolution. There have already been speculations that this may not be true, but proof was missing. Now we have direct evidence that genes were already quite complex in the first animals, and many invertebrates have reduced part of this complexity."
Not only are the introns there the team also discovered that their positions within genes have been preserved over the last half a billion years." This gives us two independent measurements that tell the same story," Raible explains. "Most introns are very old, and they haven't changed very much in slowly-evolving branches of life, such as vertebrates or annelid worms. This makes vertebrates into something like 'living fossils' in their own right."
The discovery that Platynereis also represents a slowlyevolving branch of animal life has important implications for the study of humans. "We've already learned an incredible amount about humans from studies of the fly," Arendt says. "The marine worm might well give us an even better look at important conserved processes. Another thing that this has shown us is that evolution is not always about gain; the loss of complexity can equally be an important player in evolution."
Source article: Vertebrate-type intron-rich genes in the marine annelid Platynereis dumerilii F. Raible, K. Tessmar-Raible, K. Osoegawa, P. Wincker, C. Jubin, G. Balavoine, D. Ferrier, V. Benes, P. de Jong, J. Weissenbach, P. Bork and D. Arendt. Science, 25 November 2005
If the major physiological difference between two species is that one has a shorter gastrointestinal tract resulting in a lower digestibility of foods, thus requiring slightly different dietary needs, would these critters be different 'kinds'?
Not a difference in kind. That could be microevolution as usual or one designer copying another, but they have the same body parts and the same basic sort of plan. A better example would be ducks and penguins, again same basic body parts and actually the same basic plan for life if you view what the penguin does as "flying" through water.
Please can you supply the biological definition of a "kind".
Please can you supply the details of the physical mechanism that prevents a large number of tiny changes accumulating into the evolution of a different "kind".
RODHOCETUS BALOCHISTANENSIS, a newly discovered species of ancient whale, is reconstructed here. Discovered in 47-million-year-old deposits in Pakistan, this beast had well-developed limbs that would have enabled sea-lion-like locomotion on land.
Source: Whence Whales?
Not a difference in kind.
Yet frogs are vastly different to toads. Far more different than say chimpanzees and gorillas. Do you think that chimps and gorillas are the same kind? What about chimps, gorillas, baboons, gibbons, and orangutans?
I've alrady done that above.
>Please can you supply the details of the physical mechanism that prevents a large number of tiny changes accumulating into the evolution of a different "kind".
It's called "natural selection", and that is precisely what it does.
Yet they who evolved the slowest, evolved the most, while they who evolved the fastest evolved the least....that seems a tad illogical
What significant difference between dogs, wolves, and cats (and BTW when you say cats are you distinguishing between lions, tigers, pumas, lynx, panthers, cougars, wildcats, domestic cats, cheetahs, leopards) would prevent what you would term cumulative microevolution from bridging the gap between them, in the same way for example that finches can develop different beaks?
Stasis only results from natural selection when there is no change in the organism's environment or relationship with other organisms. Your link brings up evolution of the flagellum which, while interesting, is another subject entirely.
You concede that frogs and toads might have a common ancestor, which places "kind" at the family level. As pointed out, though, frogs and toads have a lot of key differences. How is it that frogs and toads (both members of the order Anura) can all have a common ancestor but not cats and dogs (both members of the order Carnivora)? The level of difference is comparable.
Also is it possible that frogs/toads (order Anura) and salamanders (order Caudata) are the same "kind"? Transitional fossils (like the one I posted earlier) and the existence of Ascaphidae (frogs with vestigial tails) seem to conribute evidence to this. If they're not the same "kind", where does the inability of one "kind" to evolve to another begin here? If they are the same "kind", this pushes the category of "kind" back to the level of biological Order.
This "kind" thing is very confusing. I vote we scrap it.
That bothered me a bit also. It seems our species has come a VERY long way from the ape-like creatures in 5 mm years. Hard to reconcile--PH, any thoughts?
Someone else has already given one of the obvious rejoinders to the "stasis" element of your link. So I'll address the "of what use is 2% of xxx?" element. The answer is actually a great deal. For example an eye that is 1% as effective as the modern vertebrate eye would give its possessor a literally killing advantage over completely blind opposition. Likewise a fin that was 1% of the way towards being a leg would allow a fish that lived in shallow water marshes massive advantage over its competitors, particularly at a time when the land lacked all animal competition. The "of what use is x%" argument is essentially an argument from incredulity, and points to a failure in the imagination of those posing it.
It's an in kind development grant for the scientifically illiterate.
You are soooo kind.
That's "kind" of the whole point here, and why taxonomists don't use it a a classification scheme.
I think it's sloppy writing. Perhaps the intent was to say that because our species appeared so recently -- less than a million years ago (give or take) -- then our evolution took a long time, thus we were "slow" to arrive. Nothing else makes any sense.
Basically the whole "kind" thing comes from people whose level of biological knowledge appears to be at "The Big Picture Book of Animals" that we all loved when we were 5 years old. In books like that frogs and toads get lumped together (if toads even get a mention) and the entire insect kingdom gets one page and three species if you are lucky. No wonder that some people find Noah's Ark possible.
Well, I'm glad I was not alone in being confused. Your explanation could be correct--and if that's it, some very sloppy writing on their part. Thanks.
Funny, statisticians have no problem with the concept.
So are you saying A rat is a pig is a dog is a boy.
Doubtless that is some kind of brilliant rejoinder that means something to you, but you'll have to run it by me in smaller stages so I can get what you are saying.
Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.