tag:blogger.com,1999:blog-6030110973061875792.post2268219353994054560..comments2024-03-16T21:32:23.088-04:00Comments on A Sure Word: 10 Evidences for Biblical Creation: Part 3RKBentleyhttp://www.blogger.com/profile/00566375018731000081noreply@blogger.comBlogger3125tag:blogger.com,1999:blog-6030110973061875792.post-63713086840817057382016-01-31T19:07:16.684-05:002016-01-31T19:07:16.684-05:00Richard Owen, contemporary and opponent of Charles...Richard Owen, contemporary and opponent of Charles Darwin, defined "homology" as "the same organ in different animals under every variety of form and function." This is often illustrated by comparing, e.g. the forelimb bones (humerus, radius, ulna, carpals, metacarpals, phalanges) in, e.g. a whale's flipper, a dog's foreleg, a human arm, a bat's wing, etc. These don't serve the same function, yet clearly corresponding parts are in the same places. To paraphrase Owen, these are cases of detailed similarity in structure that are not required by similarity in function.<br /><br />Before evolution was posited as an explanation for homology (and incorporated into common definitions of "homology"), and indeed before "homology" was named as such, such detailed, seemingly unnecessary similarities were used by (creationist) Linnaeus to classify organisms into the same genera, orders, and classes. Similar structures serving similar ends can be explained by either common design or common descent, but similar structures serving dissimilar ends ("parahomology"), even while in other cases dissimilar structures serve similar ends (e.g. the inverted retinas in vertebrate eyes and the "right-way-round" retinas in cephalopod eyes), argues for common descent with opportunistic, uncoordinated modification in different lineages. It is these detailed similarities, existing even where it is demonstrable that other possibilities exist (because one can point to animals that have them), that are identified as "homologies" and cited as signs of common ancestry.<br /><br />Note that the same structure can be homologous in one respect and analogous in another. The wings of birds, bats, and pterosaurs all feature the basic structure of the tetrapod forelimb, but modified in quite different ways to form wings. In birds, this similarity is retained in the vestigial wings of flightless birds. They are homologous as forelimbs, and analogous as wings. Note that, within marsupial and placental moles (or several other pairs of similarly-adapted marsupial and placental species), analogous adaptions are built up from homologous structures inherited from a Jurassic-period common mammalian ancestor; they end up looking more alike than, e.g. wings in bats and birds modified from mammal and reptile precursors respectively.<br /><br />One other note: "uselessness" is not really part of the definition of "vestige." Darwin argued that a structure could lose its main more most conspicuous function while remaining perfectly functional for some lesser function; Weidersheim went so far as to include cases where a structure had lost one function in order to gain a different one (so that, e.g. a seagull's wing is a "vestigial" grasping arm). Most evolutionists are content to call that, as noted, "parahomology" rather than a "vestigial organ." And, analogously on a small scale to the convergence between marsupial and placental moles, an extension (caecum) to the large intestine might have evolved multiple times to help digest leaves, and then independently become vestigial in multiple lineages: analogy heaped atop and built out of underlying homology.Steven J.https://www.blogger.com/profile/15638850493907393069noreply@blogger.comtag:blogger.com,1999:blog-6030110973061875792.post-79152289357452595532016-01-31T18:42:29.829-05:002016-01-31T18:42:29.829-05:00Regarding plover-crocodile symbiosis, I would supp...Regarding plover-crocodile symbiosis, I would suppose that crocodiles aren't always hungry. Even warm-blooded animals that size aren't always hungry, and crocodiles are cold-blooded. It might refrain from eating a bird that approached it and picked the crocodile's teeth while the croc was relaxing after a meal. Over time, selection would favor both bolder plovers and more cooperative crocodiles. Occasional, very cautious behavior becomes common, bolder behavior, becomes habitual, casual behavior -- or tolerating a bird because one isn't hungry gradually becomes tolerating it all the time (because ancestors who refrained from eating the bird had better dental health and ended up feeding better on things other than plovers).Steven J.https://www.blogger.com/profile/15638850493907393069noreply@blogger.comtag:blogger.com,1999:blog-6030110973061875792.post-10643268285061922122016-01-31T18:33:21.841-05:002016-01-31T18:33:21.841-05:00Mathematical models of natural selection typically...Mathematical models of natural selection typically posit a "fitter" variant giving its bearer something like a one percent better chance of passing on its genes to the next generation, compared to its contemporary conspecifics. Suppose there is a predator species X, a prey species Y, and a (poisonous or otherwise dangerous) non-prey species Z. Some members of Y bear a slight, partial resemblance to Z. If an X gets a good look at a Y, that slight resemblance won't fool or deter it for a moment -- but on occasion, X will get only a glimpse of a slightly Z-like Y and mistake it for a real Z -- and go seek other prey. So in each generation, these slightly Z-like Ys will be a little bit more likely to pass on their genes -- including the ones for a vague resemblance to Z, which will spread through the population.<br /><br />Now, members of Y compete not only -- or even mainly -- against predators like X or against their own prey, but against each other. When nearly every Y is vaguely Z-like, the advantage of that slight, partial, resemblance shrinks. Now, individuals who are a little more like Z (what Z is like now, not like what it was many generations ago or will be like many generations from now) will have the advantage -- the advantage of being just a little bit less likely to be eaten before they reproduce. It's more or less the same principle as a casino's edge on a roulette wheel -- the advantage is small, but over time and many incidents it really adds up. And the resemblance accumulates, step by step and mutation by mutation, until it is very close indeed.<br /><br /><i>Mutatis mutandis</i> (no pun intended) this works for other sorts of camouflage: looking very slightly more like a leaf or twig may save you (quite possibly at the expense of a very slightly less camouflaged conspecific), if a predator is faced with bad lighting, or seeing you from a distance, etc. Again, each tiny incremental improvement gives your descendants their own small edge -- you hid a bit better from predators than do other members of your species, or sneak up on prey better, or both.<br /><br />Why is it more reasonable to suppose that the Creator made the two species look alike, or made some animals look like plant parts, etc.? Why does the Creator make predators -- and then make their prey harder to find (especially since, as noted, the advantage is over other prey, that gets eaten instead of the well-camouflaged individual)? This is design working at opposite purposes simultaneously.<br /><br />In another forum, some years back, it was pointed out that intelligent design proponents don't get to use the "just-so" story objection. Evolutionists can use it against other evolutionists, since [a] there might in fact be some unknown reason (not just gut feeling) why the posited selective regime wouldn't work, or [b] there might be multiple other possible selective regimes that would work as well. Note that "b" doesn't help you a bit and, from your point of view, "a" is just wishful thinking unsupported by evidence.Steven J.https://www.blogger.com/profile/15638850493907393069noreply@blogger.com