Because in the embryos of more complex organisms you always first see the same design. This is Ernst Haeckel's theory which he calls "biogenetic law," (and he IS partially wrong: it cannot be considered as a "law") so if I don't explain it enough, research it on google using those terms, as I will not be able to reply until next weekend. The basic embryo of a fish with gill slits appears in all initial embryos of amphibians, reptiles, birds, and all mammals: evolution in action. This is also true of the notochord and a tail, which in a fish is just an elongation of its hind fin: the tail of amphibians, reptiles, and mammals gradually decreases until humans have no tail at all. But in humans and other taxa embryos, the tail is the most dominant projecting structural part of the initial embryo. Why does it disappear? The gill slits though are the most basic example of how evolved species retain ancestrial traits in their embryos. In fish, first they served to take up oxygen in the water for respiration. But then the frontal gill slits evolved into jaws - jaw fishes - but in the initial embryo you can't tell any difference. Then in amphibians these gill slits form what is called a "buccal cavity" in adults that allows "fresh air" into the correspondingly evolved lungs. The same identical gills slits are still there in the embryo of reptiles, birds, and mammals, but the end result differs. In vertebrates these gill slits in the embryo no longer evolve into ANY role in respiration. Some of the gill slits form the jaw, others just close up entirely, while others evolve into parts of the pharynx and the tongue bar. So basically, Haeckel's theory, "biogenetic law," is not entirely incorrect. Each evolved species still contains ancestrial remnants of what came before it - but maybe not all. In my opinion I think that this is why dolphins and whales were able to easily and quickly (in terms of geological time periods) re-evolve fins to readapt to life in oceans without going extinct. These remnants of ancestrial traits constantly pop up as "abnormalities" in other animals as well. For example, horses original had four or five digits, just like humans and other tetrapods, but they gradually evolved into a single-toed horse: a single hoof. Yet occasionally horses are still born with extra toes sticking out from the sides. These are ancestrial remnants carried over from their original genetic makeup still present in their initial embryos today.
No. I meant accumulation of a given allel in a population. Evolution has a genetic basis, not a phenotypical one. A single base exchange can lead to the same amino acid and thus apparently not lead to a phenotype. But for instance lacking the given t-RNA can lead to further downstream consequences. Again: evolution is basically defined as the change of allel frequency. Evolution doesn't happen to individuals, but to populations. Furthermore, evolution can lead to a change in phenotypes, but doesn't necessarily do so.
Does your DNA change in the course of a lifetime? I have heard different accounts, and I have heard that we just don't know yet.
I don't think we have a difference here. We are both saying that the genotype basis first originates as an "accumulatative" allele mutatation at a loci within a population (and I use the term loci rather than locus because almost all most phenotype traits are changed and are due to more than one locus).
One raven Just in order to clarify things (and pardon me if it is somewhat trivial, but better safe than sorry): allels are variants of a given gene on a given position on the chromosome (locus). Usually by mutation (e.g. an error during duplication) or recombination events (e.g. during meiosis) the base sequence of the allel can be changed, thus leading to a change in the allel. The variations can in theory be as small as a single base exchange. Depending on whether there is an amino acid exchange in the resulting protein there can be a change in the activity of the protein and possibly leading to certain phenotypes (although even a "neutral" mutation could have effects but let's leave it aside for now). So given these mechanisms, there is always a certain variation in the gene-pool of a given population on which natural selection can work as you pointed out correctly in you post. Now to why lamarckism does not work. As evolution is a change in allel distribution, it has to be inherited to the next generation. Now the activities of a given during its lifetime organism does not permeate to it's gametes, and thus it cannot be a factor in evolution.
Basically yes. Mostly due to random mutations and of course not globally but always only i a limited amount of cells. Only changes that occur in your gametes are inherited to the next generation. Valich: There is not need for the accumulation of mutations. And as I said, phenotypes are not a factor (although naturally selection of course only does act against them).
Meaning what? That changes that happen elsewhere are not inherited, rather you inherit what was originally there before the changes?
I am not too sure what you mean. Basically only the genetic information that are in your gametes (that is, either sperm cells or ova) are inherited to the next generation. That is the mutations are only inherited if cells involved in the production of these gametes (or the cells themselves) are mutated.
I see. So, DNA mutations happen on the single cellular level? Or is it that if one sperm cell has this particular mutation, they all will?
No, every mutation only affects a single cell (unless the cell doubles, then its daughter cell keeps the mutation too). So, a mutation in a cell of your hand will have no effect on your sperm cells. If a single sperm cell mutates, only that cell will be affected. However if the cells involved in sperm production are affected, all cells derived from them will also harbour mutations.
Near the 3rd standard deviation!? LOL! That's about an IQ of 70-80, according to classic psychometry.
Wrong! Wrong! Wrong! again. When it comes to Natural Selection, the phenotype enables the organism to better survive and is the ONLY ultimate factor that enables it to survive better than the others in the population. At this point in evolution the genotype means diddly-shit.
Valich, in case you are not able to read the topic (or follow the conversation for that matter): we are talking about evolution. not natural selection, which, I have to add, as you are obviously not getting it, is only one of the shaping forces of evolution, but not evolution itself. Really, you are likely the first one getting on my ignore list. Ever. You neither understand what others post, nor obviously your own posts. One_rave might have a slightly incorrect view of how evolution works, but at least he tries or at least gives a good impression Please Register or Log in to view the hidden image! of trying to understand. You on the other hand celebrate your ignorance. You to confuse others with random posts which include quotes that have no relavance on the matter (which is ok with me), but you also post your own terribly wrong conclusions and try to sell them as truth (which is not ok with me). For everyone with only a peripheral education it is painfully obvious that you don't comprehend what you post. While I have no problems with people not understanding things or having misconceptions (otherwise I wouldn't be able to teach students.....) I can't stand people that are actively spreading misinformation. You may remain ignorant, that's your choice. But there is no need to involve others. Didn't you ask yourself why especially the forum members that are professionals on this area (either PhDs or PhD students, from what I gather) turn against you? While I can't speak for all I do think that it is at least partly because we scientists have generally a very low tolerance against again deliberate misinformation and fraud.
OK. I'm almost there. Please Register or Log in to view the hidden image! Thanks for being patient. Now... "cells involved in sperm production"... Meaning the testes, or does it go further than that? There is something I would like you to clear up for me, if you would, or point me in the right direction. Stem cells. They have the capability to become any cell in the body, but that does not mean that every cell in the body was once a stem cell, correct? For example, sperm cells are produced in the testes, right, so are they produced "from scratch" there? Were they once stem cells? How does that work? Also, are stem cells produced your whole life? For what, specifically? And finally, to tie it all togethaer, and maybe give you an idea of my thought process, does the brain stem use a "blueprint" of some srt to create stem cells, and how (if it is possible) would that "blueprint" cause a mutation in ll the stem cells that are produced from then on? Is there anything that can happen to cause a shift in production like that to make a "permanent" mutation in the cells produced by the body? I am sure it is clear from my "description" that I do not understand stem cells and the process that produces them at all, but I hope you can understand my series of questions, regardless. What I am looking for, is a mutation that would not just mutate a cell, but would mutate the stem cell production process (asimilar to the scenario you pointed out with the sperm cell production process). I know I asked a lot above, and if you don't want to go through the work of explaining it all to a layman, maybe you could point me in the direction of a good source (web or book)? Thanks for whatever you can do.
Specialised cells in the testes that undergo differentiation into sperm cells (called spermatogonia, I think.. am not sure, though). Nope. I suppose you are talking about embryonic stem cells of the blastocysts. Later on most of the stem cells are lost (or rather they differentiate into specialised cells). There are few remaining somatic (or adult) stem cells, but their origin is not quite clear (at least as far as I know, I am not expert on this field). So the bulk of cells in an adult organism are not directly derived from stem cells, but rather by cell division of differentiated cells. I think this answers also most of the further questions you have, as it is clear that stem cells in adults are few (like in bone marrow) and they appear to be a bit more specialised than embryonic stem cells (that is their ability to differentiate to different cells appears to be more limited). Due to their underrepresentation a mutation in a stem cell won't result in drastic changes (as single mutations in other single cells). Regarding production of cells, basically any cell is derived from cell division. So there is not master system producing a lot of different cells like a cell factory, if that's what you are thinking of. For more info try this: link
Again, resorting to whether you or not anyone else has a BA or PhD is totally irrelevant. So why do you even mention it???You assume I don't have a PhD? I have consistenty argued against solely on the theory ogf Natural Slection by inroducing numerous examles of human "Artificial Selection." But it seems that everyone else has a "peripheral education" on this subject.Futrther, no one out there seems to understand how thermodynsmics applies to biological evolution???
