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Cathe
Join Date: Sep 2007
Location: Oregon
Posts: 1,016
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Quote:
Originally Posted by owen06
Hemoglobin type "S" is the type of hemoglobin associated with the development of sickle cell anemia. In people with only one copy of the gene, when they get infected with malaria, hemoglobin type S is basically activated to the point that the cells become deformed, and are then killed. This prevents the parasite from spreading throughout your body. The problems occur when people have two copies of the gene. People rarely have two copies.
Maps plotting the malaria endemic parts of the world, coinside with maps plotting prevelence of the sickle cell gene. So sickle cell is actually a positive trait but adaptation isn't perfect and sometimes you end up with two copies of the S gene. People who had two copies didn't usually live for long (this has changed due to medical advances). The adaptive advantage of having one copy of the S gene is balanced by the negative effect of having two copies. Thus, people in high malaria areas were naturally selected to have one copy of the type S gene (which is positive) and people with two copies were selected out.
I would also like to point out that modern science doesn't actually use the traditional evolutionary tree, however, with advances in technology, science has been able to analyse protiens that make up every living thing. Because we know the rate that these proteins change, we can plot the divergence of the various species on earth. We can actually show that mammals and insects both divereged from the same common ancestor as plants, at the same time. I'm not discounting that adaptation occurs (i.e. Darwin's finches).
With regards to adaptation in one generation, are you referring to definitive, structural changes or modifications in gene expression? I disagree with the former but agree with the later. If there are two populations of the same species, each having to adapt to different environments, over time, the sum of those adaptations could make it so that those two populations could no longer successfully reproduce with one another and they would now have evolved into different species. Therefore, adaptation is the process by which evolution occurs.  |
Sickle cell anemia reduces the fittness of the population even in some of those with the trait, or recessive gene and there for is not a positive overall trait. The fact that a virus may not be able to live in this particular environment does not even constitute an argument for adaptation and results in an over all loss of genetic information which is not evolution or even macroevolution.
"Many individuals will have decreased ability to concentrate their urine. There may be an increased incidence of urinary tract infection during pregnancy. Painless hematurea does occur in 1 to 4 % of individuals with sickle cell trait . This complication is usually not a significant problem, however, a minority of individuals may have significant problems with recurrent hematurea requiring medical intervention, transfusion, and iron therapy. Complications such as splenic infarction, pain episodes, and sudden death may be induced by severe hypoxia, severe dehydration, and exertion at the limits of human endurance."
"If there are two populations of the same species, each having to adapt to different environments, over time, the sum of those adaptations could make it so that those two populations could no longer successfully reproduce with one another and they would now have evolved into different species. "
Any ornithologist will tell you that a species is an artificial designation defined by those whoever is needing the funding at that time. Consider the Bard owl and the Spotted Owl, with out mans help eventually the Bard owl will win out. But they are still both owls.As the Bible says, they reproduce after their KIND. There is no evidence of evolution between kinds. Only adaptation, which some scientists prefer to label MICROevolution. A donkey plus a horse equals a mule. Clasified as an entirely different species. It is still equine and NOT fertile. As for genetic similarity: read the following from ICR on the subject:
Many secular scientists have used this information in a variety of ways to support evolutionary hypotheses about human origins and the origin of all life forms. At ICR, we have also begun to investigate the field of genomics to provide scientific evidence supporting the Biblical position that man was created distinctly different from the animals, and that each "kind" of animal was created distinctly different from other "kinds."
One area of research currently being conducted at ICR is a comparison of the human and chimpanzee (Pan troglodytes) genomes. The Biblical teaching that man was a special creation (Genesis 1:27), different from any other created "kind," is contrary to the evolutionary paradigm that man evolved from a primitive ape. Following the evolutionary line of reasoning, evolutionists have proposed that the chimpanzee is the nearest relative of modern man--both have evolved from a common hypothetical ancestor. Evolutionists are using certain fossils and the general similarity of man and chimpanzee as proof of their common ancestry. As molecular data (including amino acid sequences in proteins) have accumulated over the past thirty years, this evolutionary link has supposedly been confirmed. Many protein-coding sequences in the genome have been reported to have a 98.5% sequence homology (the percent of DNA that matches between two organisms) for humans and chimpanzees. However, such sequence similarity was based only on a fraction of the total genome of man and chimpanzees, and reflects only the physiological similarities of humans and chimpanzees based on their cellular protein content, not the overall genomic content. The homology frequently reported for the human/chimpanzee genomes excluded "indels," which are areas with zero sequence homology. In a recent analysis by Britten et al., inclusion of "indels" in human and chimpanzee sequences reduced the human/chimpanzee homology to 95%.3 However, preliminary research at ICR using genomic databases and the current literature indicates that the sequence homology between humans and chimpanzees may be less than 90%, as more genomic regions, such as heterochromatin (regions of condensed noncoding DNA) and unresolved alignment gaps are included in homology studies.
Major differences between the human and chimpanzee genomes are increasingly being documented in scientific journals. An example of this was reported in an article in Genome Research identifying chromosome rearrangements between human chromosome 21 and the homologous chimpanzee chromosome 22.4 Using many long-range human PCR primers (primers used to sequence 10,000 bases at a time) that spanned 32.4 Mb (1Mb = 1 million bases) of human chromosome 21, approximately 27 Mb of chimpanzee chromosome 22 were successfully sequenced. This left 5.4 Mb of corresponding human sequences undetectable in chimpanzee chromosome 22. Assuming the 5.4 Mb of DNA that was unable to be sequenced in the chimpanzee genome was 70% homologous to the corresponding human sequence (very generous for sequences that are not alignable!) and combining this with the 27 Mb of sequenced chimpanzee DNA (assuming this region is 95% homologous, see above) would give a homology of 90% for human chromosome 21 and chimpanzee chromosome 22. If the unalignable region is less than 70%, the homology of human chromosome 21 and chimpanzee chromosome 22 will be even less than 90%. Considering all the elements that determine sequence homology, when an entire sequence comparison is finally made between the human and chimpanzee genomes, the actual amount of DNA sequence homology is almost certainly going to be less than 90%.
What is the significance of 98.5% versus 90% homology? If the human and chimpanzee genomes are 10% different, it rules out the possibility that humans and chimpanzees evolved from a common ancestor. If the difference between the two genomes is 10% then the total number of differences in the DNA sequence would be approximately 300 million nucleotide bases (10% of 3 billion nucleotides present in humans or chimpanzees), meaning that 150 million bases in both the human and chimpanzee have mutated and been fixed in the population since the last common ancestor. If the hypothetical divergence of humans and chimpanzees occurred about 5 million years ago and given that a human generation is about 20 years (and a chimp slightly less), then 250,000 generations have passed from the time humans and chimpanzees diverged from a common ancestor. To get 150 million nucleotide changes in 250,000 generations, the two lines of descent would require 600 beneficial mutations fixed in each population of ancestral humans and chimpanzee per generation. However, nearly all mutations are neutral, having no effect and therefore are not selectable, or are slightly deleterious, causing genetic deterioration in a population of organisms. A few beneficial mutations have been observed, such as mutations that confer antibiotic resistance in bacteria and sickle cell trait in humans. But even these mutations are deleterious when the individual is returned to optimal conditions for survival and forced to compete with other individuals lacking the mutation. Recognizing the high genetic cost of fixing any mutation in a population, J.B.S. Haldane, an evolutionist, determined mathematically that it would take 6 million years to fix just 1,000 beneficial mutations in humans through natural selection.5 If only 1,000 of the mutations are beneficial, then nearly all of the 150 million mutations in the human lineage would be slightly deleterious or neutral. Deleterious mutations would lead to degeneration of the genome resulting in extinction, and the neutral mutations would cause no change. This does not lead to some "great leap forward" to a more adapted creature. Because there is no feasible evolutionary solution to this problem, this whole situation has been termed "Haldane's dilemma." Even if the difference in homology of humans and chimpanzees is just 98.5% there still would be 250,000 beneficial mutations to be fixed in both populations in the last 5 million years, far too many than are feasible by Haldane's calculations.
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