Posted on 05/03/2005 2:12:35 AM PDT by Cincinatus' Wife
Not all mutations are beneficial, but an adaptation pretty much by definition would always be beneficial in the short term. Even then, there's such a thing as an evolutionary blind alley.
My point was that what you said is simply true per definition.
Evolution is descent with modification and therefore you get a treelike structure. So if you pick one subtree and assign it a label, like "bird" for instance, this particular subtree will remain the "bird" tree no matter how many new branches it sprouts.
But don't let this fool you. Just because a new species (after millions of generations) is "still" a bird doesn't mean it must look anything like an extant bird species. However, it should still be obvious that it descended from a present bird species even if it might look quite different.
I don't think evolution would ever lead me to a crisis of faith. However, if Genesis was proved beyond and to the exclusion of any reasonable doubt (criminal guilt standard), I would absolutely question what the point of the Bible was. If the Bible isn't true, then, of course, it is useless - no better than any other philosophical writings. As of now, I'm not worried, though - lol.
By the way, I found what I think is a good, relatively simple, dinosaur site. And you can ask scientists questions. I'm curious if we asked several respected scientists the same question, how similar or different their answers would be. If I have time, I will. Would be interesting. Of course, I understand much of science isn't exact and I would expect some differences of opinion.
http://www.madsci.org/posts/archives/jul99/933425416.Zo.r.html
Thanks again.
Do you think this man is stupid?
http://www.christiananswers.net/dinosaurs/bio-parker.html
Do you have any idea how many bright people with similar degrees disagree with him?
So did you read the post on the retrovirus insertions in Human and simian DNA and how it matches with the expected speciation dates in the past?
Then the similar results on many other DNA foibles?
Your only resort to such evidence is to claim that God placed these DNA markers in place merely to make us think evolution happend and thus question our faith.
Or, perhaps you just interpret Genesis wrong, and God created evolution first.
I'll bet the post I linked is longer, by far, than the whole creation story in Genesis. The Bible just doesn't have any detail on how God performed His creation. And I wouldn't expect it too anyway. Teaching you Biology isn't it's purpose.
I saw the thread when it started and just typed in a comment on the fly, never dreaming it would get to have 500+ posts, so I hadn't checked back in on it until I saw your comment here. (I get super busy on my database work!) Sorry for any perceived delay.
When I was at MIT, I majored in mathematics, (Course XVIII), and also computer science, back when it was a subset of Electrical Engineering (Course VI), just becoming its own major (1970). To illustrate how much it was originally electrical engineering, we took courses in transistor theory, circuit design and analysis, queuing theory, probability, and so forth. We never heard of spreadsheets and whatever else is under computer science these days.
I didn't even know anyone in biology, since I don't believe that MIT did health sciences and life sciences very much. About 90% of my classmates were in engineering, math, and computers.
Overall, my perspective on this fascinating subject is one of individualism and unwillingness to be expected to accept the majority opinion without what my mind acknowledges as proof. On campus, I was in a very small minority of political conservatives, and being openly Christian and faced with bemusement and/or hostility merely reinforced my independence of thought.
All the material I have ever read just seems to me to be mathematically suspicious (regarding probabilities of chance events working out so well), as well as being based on a presupposition that not only is evolution true, it is the most true thing there ever was, and one gets treated with scorn for resisting the obvious truth.
Does it become less exact on a larger scale than a smaller scale? Or less exact in more complex life forms or does that make a difference? Would you expect more variation in humans than say, fruit flys? I know - fruit flys have a lot of similar DNA to humans (or so I've heard). Thanks.
If you're asking about the "raw" mutation rate -- the rate at which changes occur within the genome -- it does vary among different species, but not in the way you presume.
In general (but with many exceptions), the more "complex" organisms have *lower* mutation rates, not higher. The reason is that with more complex cellular machinery, it opens the door for more complex, more varied, and more effective mutation prevention strategies, and more effective repair mechanisms.
Also, complex organisms had to evolve such "anti-mutation" protections for the simple fact that for a given mutation rate, a longer (i.e. "more complex") genome will suffer proportionally more total mutations than a shorter one (e.g. twice the genome length, twice the total mutations at a given mutation rate).
So as genomes grew in order to contain more genes, it became more important to find ways to lower the mutation rate (per basepair per year) in order to keep the total number of new mutations per generation from growing dangerously large. On the other hand, simple organisms (those with small genomes) with short generation times (and/or which produce large numbers of offspring) can tolerate much higher mutation rates and still have a good statistical chance of producing workable copies of themselves.
I wanted to include a table of the different mutation rates for various organisms, but it's actually rather hard to draw together information from various sources into one table in a way that they can be directly compared. The reason is that the mutation rate can be measured in several different ways, and the way in which a given study will choose to measure it for the organism being studied will vary depending upon what exactly the researchers were wanting to measure. For example, I've run across mutation rates measured in most of the following ways (each of which is useful for different purposes):
"Mutations per X per Y",This makes at least 16 different measures of mutation rate...Where X can be any of:
per basepairAnd Y can be any of:
per total genome
per effective genome (i.e. that portion of the genome which "matters")
per generationper year
per year since last common ancestor (measured as the number of silent mutations actually accumulated via genetic drift in a given lineage)
per replication (i.e. cell division)
per generation
To complicate matters, some particular types of mutations occur at a steady rate over chronological time (for example mutations induced by background radiation or chemical free radicals), whereas others occur as a result of DNA replication itself (for example copy errors), so each of the different ways of measuring "mutation rate" may not be comparable to the others, depending upon the generation time or number of cell replications for a given species (since the different measures will include differetn mixes of the "per time" and "per division" mutation types).
But with that caveat in mind, here are some various mutation rate measures:
Coronaviruses (a type of RNA-based virus, which includes the virus causing Hepatitis) have a high mutation rate, resulting in an average of three mutations per genome per generation.
The copy error rate (*only*) for E. coli is 1/10^8 basepairs per replication.
The human mutation rate is around (1 or 2)x10^-8 per basepair per generation. Given the human genome size, this means that each human contains around 100 novel mutations in their genome. However, it is unknown what portion of those occur in "junk DNA", result in silent basepair substitutions, homologous amino acid substitutions, etc. -- likely well over 90% of them are neutral in various ways.
The replication accuracy of HIV (the virus which causes AIDS) is so sloppy that even though the HIV genome is only 9000 basepairs long (compare to humans with a genome 3,000,000,000 basepairs long), its error-prone replication results in one or two new mutations every time it replicates, for a mutation rate of a whopping 1.7x10^-4 mutations per basepair per generation. This is actually the secret of HIV's success -- it mutates and evolves so rapidly that by the time an infected person's immunue system develops antibodies to the virus, many of the HIV viruses in their body have already changed enough that the antibodies don't recognize them. And by the time the body has produced antibodies to match the newer forms of the virus, the virus has changed yet again. In this way HIV stays one step ahead of the body's immune system, and maintains the infection for decades without being wiped out, as would have been the case for most ordinary viral infections. Eventually the body's overworked immune system collapses entirely, bringing on full-blown AIDS. Similarly, the HIV virus has proven adept at evolving defenses against the drug cocktails that have been formulated in an attempt to slow or halt its growth in the body. Like insect pests evolving immunities to commonly used pesticides, the HIV populations in even a single person's body rapidly evolves immunity to the drugs designed to block its growth, sometimes within mere weeks.
The rate of *accumulation* of neutral mutations in a population across generations in a lineage (i.e. the "molecular clock") is statistically constant for all tested mammal species at 2.2x10^-9 mutations per basepair per year. See Mutation rates in mammalian genomes. This paper also has some fascinating results concerning the times of divergence for various mammalian lineages. For example, humans and chimps last shared a common ancestor 5.5 million years ago.
One of the most cited papers on mutation rates is Rates of Spontaneous Mutation. It contains a wealth of information about how mutations occur in general, as well as specific data on actual mutation rates in various species. Also check out the links at the bottom for the dozens of papers it cites, and the dozens of papers which have cited this one -- many are available online.
This paper also contains specific information which can help answer one of the questions you ask: The mutation rate in fruit flies is 3.4 x 10^-10 mutations per basepair per replication (e.g. cell division), whereas the corresponding rate for humans is 5.0 x 10^-11 (see Table 5). So fruit flies have a mutation rate almost ten times that of humans. As I mentioned earlier, they can "afford" to thanks to their more rapid generation times and more prolific reproduction rates. Also note that while this means only 0.16 mutations on average per total genome per single human cell division, the process of developing an adult human from one original fertilized egg cell, and then producing the next generation of sperm/ovum, results in a chain of about 400 cell divisions (and 20 years of time on average) between each generation, genome-wise, so a rate of 0.16 mutations per genome per cell division corresponds to a rate of about 64 mutations per genome per human generation (as already mentioned above).
When discussing mutations, the natural follow-up question is, what proportion of mutations are likely to actually be harmful, neutral, or beneficial? Here's a paper which seeks to find hard numbers to answer that question: Direct Estimate of the Mutation Rate and the Distribution of Fitness Effects in the Yeast Saccharomyces cerevisiae . Yeast may seem a poor study subject in order to learn about mutations in humans and so forth, but despite their superficial similarity to other unicellular organisms like bacteria, yeast are actually eukaryotic organisms and have more in common, metabolically and genetically, with other eukaryotes (including humans) than they do with bacteria and other prokaryotes. This study found that in the Yeast being studied, the rate of *harmful* mutations was 1.1 x 10^-3 per genome per diploid cell division. Extrapolated to humans, the per generation rate of harmful mutations would be 0.92 (i.e. roughly one per human). The study also found that of the harmful mutations, 30-40% were lethal, whereas the other 60-70% were harmful in some way but did not completely prevent the cell which inherited it from developing or functioning.
Finally, although you ask about the mutation rate, and I've addressed that specific question, mutation rates alone are only one component of the rate of *evolution*, which might be what you're really asking about. Even with the same mutation rate, the rate of evolutionary change in various species depends heavily upon population sizes, survival pressures, reproductive rate, and a large number of other factors, and on the whole these factors make a much larger contribution towards rates of evolutionary change than does just the raw mutation rate.
"Tijuana Brass. Dey cost me cheaper"
[Thunderous applause!]
WOW! Thanks. Over my head but very interesting. I do appreciate you really smart people on here. It's like free college courses!
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