tag:blogger.com,1999:blog-6030110973061875792.post6984702099873568852..comments2024-03-16T21:32:23.088-04:00Comments on A Sure Word: 1, 2, skip a few, 99, 100!!RKBentleyhttp://www.blogger.com/profile/00566375018731000081noreply@blogger.comBlogger2125tag:blogger.com,1999:blog-6030110973061875792.post-82225459114966721382016-01-15T02:08:09.101-05:002016-01-15T02:08:09.101-05:00It's hard to imagine a scenario where a limb t...<b>It's hard to imagine a scenario where a limb that is not quite an arm but not yet a wing will be selected over a functioning arm.</b><br /><br />Take a look at <i>Archaeopteryx</i>. Beneath those flight feathers is the (lengthened, but otherwise entirely typical) forelimb of a maniraptoran theropod: fingered claws apparently quite capable of grasping. At least in birds, wings clearly remained functional as arms even after they became at least borderline functional as wings. As for other winged vertebrates, I recall that the same issue of <i>National Geographic</i> that carried a retraction of carried an article on gliding vertebrates of Madagascar: quiet a few of them survive despite having "half-formed wings" that have to do double duty as limbs and gliding wings. Actual specimens make up for the difficulty of imagination.<br /><br /><b>Oh, and by the way, we only have a handful of fossils alleged to be transitional between a forelimb and wing. The thousands of in between forms that must have existed apparently left no fossil evidence showing the change.</b><br /><br />There are extinct species known from a single, perhaps fragmentary, fossil specimen. Presumably these individuals had parents, and probably siblings, and possibly offspring of their own that existed without leaving fossils -- at least none that we have found. And, regarding fragmentary fossils, it has been quipped (hyperbolically but not without reason) that mammalian paleontology of the Mesozoic consists of the study of teeth that apparently copulated with other teeth and produced baby teeth. Presumably in life those teeth were embedded in jaws and attached to limbs, spines, etc. but for many species, these have never been found. A lot of things that existed have left shockingly sparse fossil evidence -- but one doesn't assume that something didn't exist merely because one has only a few fossils of it.<br /><br />I note in passing that the evolution of bird wings is harder to trace because few fossils retain any trace of skin covering (scales, hair, down, etc.). There are theropod fossils earlier than <i>Archaeopteryx</i>, for example, whose forelimbs can be rotated in the pattern of flapping flight (though their limbs are too short for this -- this is a case of having a feature, presumably for one function, that can be adapted to a new function with the addition of other traits, such as longer limbs). But their fossils show no trace of feathers (or anything else -- there's no particular reason to assume they <i>didn't</i> have some sort of feathers).Steven J.https://www.blogger.com/profile/15638850493907393069noreply@blogger.comtag:blogger.com,1999:blog-6030110973061875792.post-63386582317764874782016-01-15T02:07:47.277-05:002016-01-15T02:07:47.277-05:00The steps in between AARDVARK and BASEBALL are jus...<b>The steps in between AARDVARK and BASEBALL are just groups of letters that don't even make words.</b><br /><br />But the genome isn't an English (or Japanese, or Amharic) text. If you change one amino acid in a protein, you still have a protein. The change may have effects ranging from drastic (and very probably harmful) to non-existent, but it's still a protein. Your analogy imposes a constraint that doesn't exist in the process it's analogous to.<br /><br /><b>The second problem is that evolution is not a directed process.</b><br /><br />That cuts against your argument as well as for it. So what if you can't make the transition between "AARDVARK" and "BASEBALL?" Evolutionists are quite content that some evolutionary transitions are virtually impossible, perhaps absolutely so. We see some part of what was actually possible; evolution has no goals that it might fail to reach. An analogy with a fixed goal (and no alternate goals accepted) is unrealistic in that respect.<br /><br /><b>In the real word, mutations are far more likely to be neutral or harmful than they are to be beneficial.</b><br /><br />Hence the importance of noting that evolution happens to populations; it is a process of massive testing in parallel. The same offspring doesn't have to experience every single mutation, and harmful mutations tend not to be inherited, at least not beyond a few generations. <br /><br />Of course, this assumes that deleterious mutations are sufficiently harmful to significantly reduce an individual's chances of passing on his genes; your next argument deals with individuals that inherit a mix of beneficial and nearly neutral but slightly deleterious variants that started as mutations.<br /><br /><b>Over time, the ratio of </b>[very slightly]<b> harmful mutations to good mutations should become unbearable and </b>[Kondrashov]<b> says, “This paradox cannot be resolved by invoking beneficial mutations or environmental fluctuations.”</b><br /><br />The summary of the article notes that it might be resolvable by "soft selection" (i.e. if natural selection, in effect, grades on a curve rather than eliminating every genome that falls below some fixed level of genetic quality) or by "synergistic epistasis" (genes having effects in combination different from their effects separately, or genes blocking the expression of other genes). In addition, since Kondrashov states that the effect depends on the size of the genome relative to the effective size (the number of individuals who actually reproduce, which is fewer than the actual number of individuals), the paradox might be ameliorated if the genome is smaller (as I recall, a widespread estimate at the time was that we had ca. 100,000 genes; the current estimate is roughly a fourth of that).Steven J.https://www.blogger.com/profile/15638850493907393069noreply@blogger.com