Thursday, March 04 2010: Separation
"The closeness with which Hox genes regulate one another is illustrated - startlingly - by the fact that Hox genes frome one species can regulate corresponding Hox genes in another, totally different species. A Hox gene called 'deformed', for example, is involved in shaping the back of the head in flies. In addition to the DNA sequence that encodes a regulatory protein, the 'deformed' gene contains a regulatory element akin to the operator sequence that Jacob and monod found in the 'lac' operon [a group of 3 genes that work together to oversee the breakdown of lactose in E. coli]. This element is essential for the 'deformed' gene to do its job properly. Mammals, such as mice and humans, also contain a gene very like 'deformed' which is involved in the development of the back of the head, specifically part of the hindbrain. It is reasonable to suppose that the mammalian and fly versions of 'deformed' are homologues - that they share a common evolutionary descent from a gene which shaped the backs of the heads of the long-extinct common ancestor of flies and mammals some 600 million years ago. Given that all other traces of this common ancestor vanished more than half a billion years ago, it is remarkable that genes from flies and mammals can stand in for each other. In 1992, Alexander Awgulewitsch and Donna Jacobs of the Medical University of South Carolina took the 'deformed' regulator element from flies and showed that it regulated the activity of the mouse version of 'deformed', in the mouse hindbrain. To show that this was no fluke, William McGinnis of Yale University and colleagues did a converse experiment, showing how regulatory elements associated with the version of 'deformed' found in humans could substitute for the 'deformed' regulatory element in embryonic flies. These amazing results show that Hox genes have been as vital to the evolution of animal form as they are to the creation of every new animal embryo - whether fly maggot or human baby." -- "Jacob's Ladder", Henry Gee, p 179
"I believe both the existence of broad algal fronds and Eophyllophyton hints at something rather important; they suggest that marine and terrestrial plants evolved the capacity to make flattened organs long before the idea took off. We should be cautious, however, in supposing from evidence of this sort that all land plants had the genetic capability of producing leaves whenever in their evolutionary history it suited them. To reach beyond speculation of this sort, we need to turn to molecular developmental genetics, the study of genetic pathways used and reused to build organisms. Making a leaf, and much else besides, requires homeobox gene networks (also present in animals) t organize growth and development by ensuring cells take on the right form and function depending on where they are on the plant. In plants, the so-called knotted homeobox gene (KNOX) family plays a critical role in leaf formation and is present in some green algae, mosses, ferns, conifers, and flowering plants. It functions in a similar manner in different plant groups: when KNOX genes of a fern are put into a flowering plant and vice versa, they still work. In other words, plants with diverse evolutionary histories posses them and their function is highly conserved, exactly as we would expect if the genes are very old." -- "The Emerald Planet", David Beerling, pp 19-20
I'm left wondering where the evidence is for the wall of separation that evolution deniers hypothesize exists between species. They are fond of admitting (because the plain facts of reality require them to, not because it is a natural conclusion of their hypothesis) that "microevolution" (that is to say, adaptation or variation) occurs, but are equally fond of proclaiming that "macroevolution" (that is to say, speciation) never occurs. The reason speciation doesn't occur is because species represent separate kinds of god's special creation and the kinds must remain distinct. Besides, it's still "just a mosquito/horse/ape/bacterium" anyway.
Ok, so if that is the case, then why are species so goddamned similar on a molecular level?
"I believe both the existence of broad algal fronds and Eophyllophyton hints at something rather important; they suggest that marine and terrestrial plants evolved the capacity to make flattened organs long before the idea took off. We should be cautious, however, in supposing from evidence of this sort that all land plants had the genetic capability of producing leaves whenever in their evolutionary history it suited them. To reach beyond speculation of this sort, we need to turn to molecular developmental genetics, the study of genetic pathways used and reused to build organisms. Making a leaf, and much else besides, requires homeobox gene networks (also present in animals) t organize growth and development by ensuring cells take on the right form and function depending on where they are on the plant. In plants, the so-called knotted homeobox gene (KNOX) family plays a critical role in leaf formation and is present in some green algae, mosses, ferns, conifers, and flowering plants. It functions in a similar manner in different plant groups: when KNOX genes of a fern are put into a flowering plant and vice versa, they still work. In other words, plants with diverse evolutionary histories posses them and their function is highly conserved, exactly as we would expect if the genes are very old." -- "The Emerald Planet", David Beerling, pp 19-20
I'm left wondering where the evidence is for the wall of separation that evolution deniers hypothesize exists between species. They are fond of admitting (because the plain facts of reality require them to, not because it is a natural conclusion of their hypothesis) that "microevolution" (that is to say, adaptation or variation) occurs, but are equally fond of proclaiming that "macroevolution" (that is to say, speciation) never occurs. The reason speciation doesn't occur is because species represent separate kinds of god's special creation and the kinds must remain distinct. Besides, it's still "just a mosquito/horse/ape/bacterium" anyway.
Ok, so if that is the case, then why are species so goddamned similar on a molecular level?
