#7: Mimicry & Symbiosis: I just recently wrote a post about mimicry in nature. This is where one species supposedly has evolved to look like another species. An insect might look like a plant. A fly might look like a bee. A moth might look like a bird.
Looking like something else might camouflage the mimic, allowing it to hide from predators or sneak up on prey, or it might fool predators into thinking the mimic is too dangerous to eat. In many cases, the resemblance is uncanny; it's far too similar to be an accident.
According to evolution, the mimic would have had to evolve the similarity gradually. One generation is only slightly like the model, a later generation is a little more like the model, a later generation even more similar, et cetera. The problem with this theory is that evolution is not a directed process. Natural selection did not know the mimic should later look like the model.
The other problem is that the model is also believed to have evolved so over the millions of years that the mimic was evolving to look like the model, the model was also evolving: model changes – mimic changes – model changes – mimic changes. That something like mimicry could ever happen by undirected processes is incredible. To believe it has happened the numerous times we find in nature is laughable. It is much more reasonable to believe the creatures were designed to look similar.
There are thousands, maybe millions, of instances of mimicry and symbiosis found in nature. Two, unrelated species strongly resembling each other is hard to explain with evolution. Believing that it happens time after time after time after time by sheer chance is impossible. To be sure, evolutionists have offered explanations. I find them to be more like “what if” stories than real science. Believing that similarities or symbiosis among different species is the result of design is far more reasonable.
#6: Homoplasy: According to evolutionary theory, some animals share similar features because they have a common ancestor. However, some creatures have features in common even though they aren't closely related in an evolutionary sense. Homoplasy, also called convergent evolution, is the term used to describe similar features in species of different lineages.
It's easy to understand why two (supposedly) closely related species would resemble each other. It's harder to understand why two, distantly related species would resemble each other. This isn't mimicry, as described above, but the problem for evolution is very similar. For example, placental and marsupial mammals are believed to have diverged some 160 million years ago; why would marsupial moles and placental moles resemble each other since they're not closely related?
The usual evolutionary response is that “form follows function” and two animals can have similar features because they've evolved to live in similar environments. The problem I see in this explanation is that if similarities are not necessarily the result of common ancestry, how can they ever be considered evidence of common ancestry?
Humans and chimps, for example, both have an appendix. Most evolutionists will claim this is the result of us having a common ancestor. However, possums (another marsupial) also have an appendix. Humans are not considered by evolutionists to be closely related to possums so the appendix would have had to evolve independently in each creature. Yet the appendix is considered vestigial in humans – a useless evolutionary left over. It may have once had some function but apparently not such an important function that we can't live without it. Why would such an allegedly non-critical organ evolve independently in different species?
Evolution doesn't occur at all, of course, but I can at least understand in theory how analogous structures might evolve in distantly related species. However, the existence of similar vestigial organs in different species is much more difficult to swallow. Evolution is a very weak explanation of homoplasy. It's not hard at all to see how different creatures could have been created with similarities. Creation is the better explanation of the evidence.
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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.
ReplyDeleteNow, 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.
Mutatis mutandis (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.
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.
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.
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).
ReplyDeleteRichard 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.
ReplyDeleteBefore 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.
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.
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.