In
scientific circles, the word, “theory” has a technical meaning
(unless you're talking about the origin
of life, in which case “theory” means “wild guess”).
According to Wiki,
a scientific theory is, “a
well-substantiated explanation of some aspect of the natural world,
based on a body of knowledge that has been repeatedly confirmed
through observation and experimentation.”
I'm not going to quibble over the definition. Instead, I want to
highlight to word, “explanation.”
Technically, a theory starts with a hypothesis but, again, I'm more
interested in the explanatory aspect of theories so I'm going to use
the word theory a little more casually. In less formal words, a
theory is an attempt to explain what something is or why it is that
way. Sometimes, evolutionists chide creationists over the latter's
use of the word, “theory.” However, the common understanding
that theories are attempts to explain data, is the bottom line in the
understanding of both sides.
What
is a fossil? How old is it? Why are rocks laid down in layers?
What are stars? How far away are they? Why do bird wings resemble
reptile claws? These are the types of questions some people ask and
our theories are our attempts to answer them. When we come up with
our explanation, we want to consider every relevant piece of data.
Your theory should explain how all the available “evidence” fits
together. A good
theory should explain all the data well.
Evolutionists, of course,
think their theory is the best explanation of all the available
evidence. That's why they think their theory is the correct
explanation. A problem arises, though, when they start saying that
there is evidence “for” their theory. That implies that the
evidence is somehow exclusive to their theory. It's as though they
want to claim a monopoly on fossils, or rock layers, or the oceans,
or the stars, etc.... Once this happens, the theory of evolution
becomes barely more than a circular argument.
I've
used this example before but I think it illustrates this phenomenon
well. Suppose you and I were walking along on a beach and we find an
unusual looking rock. It's black with uniform, purple lines on it.
I propose a theory: “I think aliens painted these lines on this
rock.” You answer, “What evidence do you have for that?” I
answer, “Well, there's the rock and there are the lines. That's
certainly evidence for my theory!”
Can
you see how circular that is? Evolutionists do exactly the same
thing. How many times have you heard some evolutionist ask (or, if
you're an evolutionist, how many times have you asked), “What is
the evidence for creation?” Actually, they usually ask, “What is
the evidence for creationism?”
Anyway, such a question reeks of circularity. The evidence for
creation is the exact same evidence as the evidence for evolution.
We merely have different theories to explain the evidence.
FACT:
The bones in human arms/hands resemble the bones in chimp arms/hands.
THEORY
1: The bones are similar because chimps and humans share a common
ancestor and the modern limbs are modified adaptations of the
primitive limbs in the ancestor.
THEORY
2: The bones are similar because they were both designed by a common
Creator Who purposely made them that way because they perform similar
functions.
In
this example, what is the evidence for creation? It's that there is
similar design in unrelated creatures. However, evolutionists will
not consider it evidence “for” creation but will insist the
similarity is evidence “for” common descent. In other words, it
can't be evidence for creation because it's already evidence for
evolution. They do this every time. It's why they say there's no
evidence “for” creation. They assume their explanation is true so the evidence can only support their explanation.
Circular
arguments are notoriously self-fulfilling. Evolutionists have become
so convinced that their theory is the correct explanation that they
have become blind to any other possible explanation for the same
evidence. To them, everything in heaven and earth is now evidence
for evolution. It's as though the evidence is literally speaking to
them, telling them “evolution is true.” When they see the rocks
and trees, birds and bees, they see “evolution.” Their
explanation of their observations has flip-flopped into becoming
their observation of the explanation.
The bones in human arms and hands also resemble the bones in the wings of bats, the flippers of whales, the clawed digging forelimbs of moles, and the forelegs of elephants. There is a less obvious but still detailed resemblance to the wings of birds and to many other tetrapods. These varied forelimbs serve rather disparate functions, yet the detailed similarities -- humerus, radius, ulna, carpals, and phalanges -- are present in all.
ReplyDeleteFor that matter, consider the differences in the functions of the wings of condors, hummingbirds, ostriches, and penguins, yet the same detailed similarities that mark them all as bird wings are common to all. Common design for common function is inferior, as an explanation, to an explanation that also covers common design for disparate functions.
It has been complained (possibly by you; I don't remember) that evolutionists cite both similarities and differences as "evidence for evolution." Yet evolution is common descent (hence similarities due to inheritance from shared ancestors) with modification (hence differences, from modifications in those shared inheritances). It is relevant therefore both that we see similarities between the wings of crows (which fly) and emus (which don't), and a mixture of striking similarities and equally striking dissimilarities between the wings of brown bats and those of crows (they evolved the basic tetrapod forelimb from a common amniote ancestor, but that ancestor had no wings, which had to be separately "invented" by different sequences of mutations and selective pressures in bird and bat ancestors).
From your theory 2, we would expect bats and birds to have similar wings, since by and large they use them for similar purposes. We would likewise expect to see, on that theory, the same basic retinal design in dolphins (with the famous vertebrate "inverted retina") and in squids (with their "right way round" retina). Please note that this is not an "argument from bad design;" it is an "argument from different design where we would expect similar designs. But again, if box camera-type eyes evolved independently in cephalopods and vertebrates, we would expect some differences details due to different pathways to generally similar ends.
This is beside the point that the causes of evolution in evolutionary theory -- reproduction, inheritance, mutation, selection, genetic drift, and speciation -- demonstrably exist and do things. There are rather fewer peer-reviewed observations of new species being created directly from dirt (or extraterrestrial intelligences painting rocks, for that matter; positing an extraterrestrial agent to explain the purple-striped rock is an unnecessary and unjustified detail).
Steven J,
ReplyDeleteYou included only mammals in your list of creatures with homologous forelimbs. Did you intend to do that? Some amphibians and reptiles also have a humerus, radius, ulna, carpals, and phalanges. You mentioned that different bird species have wings similar to each other but you did not make clear the fact that they are also similar to mammalian forelimbs.
Your point that, “Common design for common function is inferior, as an explanation, to an explanation that also covers common design for disparate functions” is hardly persuasive. If you put your arms straight out to each side as though you were flying, you will see that you can rotate your palms a total range of about 270°. Most birds don't have quite that same range of movement but that same motion is necessary for a wing to create lift. The humerus/radius/ulna helps create that motion. It's a remarkable engineering feat that God used several times in different animals to accomplish “disparate functions.”
By the way, are you 100% certain that the genes that regulate these structures are the same in every creature that has them? Wouldn't that be a prediction of common descent?
You said, “we would expect bats and birds to have similar wings, since by and large they use them for similar purposes.” I would say that's absolutely not true. God had created wings in many different animals: besides birds and mammals, wings also appear among insects, reptiles (pterosaurs), fish (Exocoetidae), and even plants (maple seeds). The wings of insects are remarkably different than the wings of birds or the wings of bats, yet many insects are excellent flyers.
What we have then is a God who is able to take one design (humerus, radius, ulna) and adapt it to many different functions AND is also able to take one function (flying) and accomplish it with several different designs. Wow!!
Now, back to the point of my post. Many evolutionists say that the similarities and differences between certain animals' forelimbs are evidence for common descent. I say that the similarities and differences between certain animals' forelimbs are remarkable evidence of design. You're welcome to use your theory to explain the similarities; but don't then point to the similarities as evidence for your theory – at least not without acknowledging that I can use the same evidence for my theory.
Thanks for your comments! God bless!!
RKBentley
You included only mammals in your list of creatures with homologous forelimbs. Did you intend to do that?
ReplyDeleteI mentioned the "mixture of striking similarities and differences" in bird and bat wings. But yes, I noted the most striking and obvious cases of parahomology -- similar structures used for dissimilar functions -- first and deferred mention of subtler cases. Note that the pattern of "humerus, radius, ulna, carpals, phalanges" is found in the basal tetrapod tulerpeton as well as, less obviously, in earlier tetrapods like Tiktaalik; it's a very general feature of tetrapods that retain forelimbs.
I would say that's absolutely not true. God had created wings in many different animals: besides birds and mammals, wings also appear among insects, reptiles (pterosaurs), fish (Exocoetidae), and even plants (maple seeds). The wings of insects are remarkably different than the wings of birds or the wings of bats, yet many insects are excellent flyers.
But I was not denying that disparate, highly functional designs for basically the same function exist. I was pointing out that this is more compatible with your "theory 1" (common descent with modification) than your "theory 2" (common design for common function).
If you put your arms straight out to each side as though you were flying, you will see that you can rotate your palms a total range of about 270°. Most birds don't have quite that same range of movement but that same motion is necessary for a wing to create lift.
Yes. It would be very strange if wings had evolved even though the underlying limb structure couldn't be modified to make a functional wing. Indeed, as Darwin noted, his theory demanded that this be possible through incremental small modifications of the original structure, each by itself beneficial to the bearer. Special creation is under no such constraints, yet apparently, under "theory 2," the Creator acted as though He were.
By the way, are you 100% certain that the genes that regulate these structures are the same in every creature that has them? Wouldn't that be a prediction of common descent?
ReplyDeleteAbsolutely not, and I suspect not.
Obviously, given that biologists haven't even identified every gene in humans (never mind little brown bats or moles), and have only a vague idea of what many identified genes do, we can't be 100% certain that homologous structures in different species are made by homologous genes. Note, though, that many of the arguments on creationist sites that homologous structures are not formed by homologous genes are flawed.
For all that he was far more knowledgeable about biology and evolution than I am ever likely to be, Gavin de Beer's famous observation that, e.g. the gut forms from different parts of the embryo in different groups of vertebrates doesn't at all imply that different genes are involved: the same genes exist in every cell in the body (a few types of simplified cells like red blood cells excepted). Note that biologists have, by inserting an active version of the PAX-6 regulatory gene (from a mammal species!) into cells in the wing of a fruit fly have caused fruit fly eyes to grow on the wings (the PAX-6 gene is not normally active outside the head, even though it's present).
Jonathan Sarfati, in one of his books, has illustrations drawn from two different introductory biology texts, showing different developmental sequences for the development of frog limbs and human limbs (which on evolutionary terms are of course homologous). But these are simplified accounts; the detailed developmental stages are more similar and many of the same genes are involved in shaping both limbs (again, obviously, not all genes involved are known, nor their functions fully understood).
In principle, genes can "hand off" functions to new genes: a mutation can produce a novel allele that can perform the function of an existing allele, so that a later mutation that disables or alters the function of the older gene will not be selected against. Take sex selection: the underlying hormonal triggers seem to be the same across the bilaterians (vertebrates, arthropods, earthworms, molluscs, etc.). But the triggers that activate these hormones differ widely: the XY chromosome system has evolved separately several times, as has the alternate WZ chromosome system (used in birds and monitor lizards, but not in crocodiles, where sex is determined by temperature of the developing egg). There is one known species of mole in which both males and females have two X chromosomes, and the Y chromosome has vanished; apparently some new gene on some other chromosome now functions for sex determination (in which case, these moles may be on the verge of evolving new sex chromosomes).
Steven J,
ReplyDeleteYou said, “It would be very strange if wings had evolved even though the underlying limb structure couldn't be modified to make a functional wing. Indeed, as Darwin noted, his theory demanded that this be possible through incremental small modifications of the original structure, each by itself beneficial to the bearer. Special creation is under no such constraints, yet apparently, under "theory 2," the Creator acted as though He were.”
I'm sure you read my post because you quoted part of it. Yet you seem to have glossed over some key points. First, the humerus, radius, ulna combination is a remarkably simple, yet effective, way to allow rotation of the forelimbs. There is no requirement that God had to “reinvent the wheel” in every different creature He created. He used this clever engineering solution multiple times. However, He certainly is not constrained to that single solution. God has also invented other structures that can accomplish similar functions yet with an entirely different design. Birds fly and have a humerus, radius, and ulna. Beetles fly and do not. Penguins swim and have a humerus, radius, and ulna. Squids swim and do not.
Thanks again for your comments. God bless!!
RKBentley