Saturday, July 28, 2007

A creationism vs. evolution discussion,. Part 7

Unintelligent design

I am going to group the next four questions together, as they all cover the same topic- imperfect design.

Question 12:
We humans have lower back pain, varicose veins, and childbirth difficulties- what do these have to do with evolution?
They are shared with chimpanzees
They cannot have evolved because they are harmful
They are examples of inferior design
The correct answer is They are examples of inferior design.
One would expect that if humans were created by a perfect creator , in his image, as the pinnacle of his creation, that they would be examples of perfection in design. Alas, it isn't so. We, along with all other living things, have plenty of 'jury-rigged' and non-optimal designs that do the job, but lack elegance. Our aching backs and varicose veins are legacies of our four-footed ancestors. Humans are relatively recent bipods, and our structure is still very much like a four-legged animal. We lack the necessary musculature to strengthen our backs, and our veins are not well-designed for the pressures that an upright stance puts on them. Female pelvises are not optimally designed for the passage of large-headed infants, as the human species has only recently undergone a tremendous spurt in brain growth.

Marcsana’s response:
2. Our aching backs have nothing to do with four-legged ancestors! I would recommend researching a bit into what all is involved with walking. Bipeds and quadripeds [sic] have vastly different structures; There is no way to compare the two with any accuracy. We are created in the image of God. You do quote that correctly. But something happened in the Genesis accounts that accounts for defects. That is called sin. The curse fell on all creation which is why everything has a propensity toward death. Our DNA code was spoiled giving us our problems which have been getting progressively worse since the fall. Vericose [sic] veins are formed because the valves don't operate the way they should.

My response:
I thought we were having a discussion of science here. Do you have a non-supernatural explanation for any of this? Otherwise, it is just unanswerable speculation. If you are to take this line of defense, you might as well simply adopt the saying I have seen on bumper stickers- “God said it, I believe it, and that settles it”- it would certainly cut down on your writing load!
I am not sure what research (other than on creationist websites) you have done into the biomechanics of human locomotion.
One of the best reviews of this problem is AG Fuller’s “Emergence and optimization of upright. posture among hominiform hominoids. and the evolutionary pathophysiology of. back pain”
In this article, he postulates that the muscle stresses that lead to back pain are a result of transformation of the vertebrae. As we became upright, the transverse spinal process, to which muscles that stabilize the back attach, moved from the front of the vertebrae, where it is found in monkeys and most other primates, towards the back of the spine. While this transformation helped us carry our babies on our backs, it also led to stress on our backs. As he explains,

The human lumbar anatomy differs from the anatomy
in cercopithecoid monkeys in three major ways: 1) dorsal
repositioning of the lumbar transverse processes that oblit-
erates osseoligamentous mechanisms of spinal support; 2)
conversion of the iliocostalis lumborum muscle to a high-
leverage lateral flexor muscle; and 3) conversion of the
longissimus lumborum muscle to a high-leverage extensor
muscle. The first of these changes is shared with all the
hominiform hominoids, the second is shared with the
great apes, and the third is a feature mostly in members of
the genus Homo.
The effects of these three major types of transformation
is an increase in the degree of dynamic, muscularly driven
compressive forces on lumbar disks and a greater risk for
strains and tears in the muscles of the lumbar region be-
cause of their increased leverage. These features are evo-
lutionary innovations that suit the human body plan as
well as the evolutionary path and lifestyle of the human
lineage. They have supported an upright bipedal species
capable of carrying heavy objects and the young across
great distances, whether walking or running. In this fash-
ion they have helped our species to more or less conquer
the world. Nonetheless, these changes seem to be the prin-
cipal suspects for any relative increase in the susceptibili-
ty to back pain that humans may exhibit relative to the
other mammalian species.

You actually hit one statement right on the money- varicose veins are indeed “formed because the valves don't operate the way they should.” And why don’t they? Because these valves evolved in four-legged animals, where the trip up to the heart put less pressure on them. The purpose of our leg valves is to prevent blood flowing backwards on this trip. Because we are upright, the pressure on these valves is much greater than it was in our four-legged forebears and the valves cannot handle the increased pressure very well.

Question 13:
Which of the following animals has the most ideally-engineered eye-i.e., from an engineering standpoint, the eye that makes the most "sense" in the arrangement of its structures?
The correct answer is Squid.
The eyes of mammals, including humans, have retinas that are are inside-out. The nerves and blood vessels come out through the light-sensitive area of the retina, producing a blind spot. They then spread over the light-sensitive area of the retina, providing a barrier to light entering the eye. An ideal design would be to have these nerves and capillaries behind the retina. Human eyes aren't designed this way- but squid eyes are. Once again, why should the pinnacle of creation have an imperfect design?

Marcsana’s response:
13. This design in the eye actually protects us from damaging effects of light.

My response:
Really? Then why is the same design present in all nocturnal mammals and birds? They certainly do not need the shielding. And many squids are diurnal shallow-water or surface feeders. Why don’t they have the same protection?
In addition, even if there were some protection against excess light conferred by this design there are still significant disadvantages. Our blind spot is due to this design, as is susceptibility to blindness caused by retinal problems (not just in humans, but in other animals as well- progressive retinal atrophy, for example, is the most common cause of blindness in dogs)
As for Marcsana’s claim that “this design in the eye actually protects us from damaging effects of light,” I must presume that his argument is derived from claims made on creationist websites such as “Is Our ‘Inverted’ Retina Really ‘Bad Design’?” This page claims that the choroid (the net of blood vessels over the retina) acts as a “heat sink” dissipating away heat generated by light striking the retina, at the same time that it brings nutrients to the energy-demanding retinal cells.. It references several papers (most published over 40 years ago) on this issue- but, as is usual for creationist articles, provides no direct links to the articles cited. Actual articles on the choroid, such as this one paint a different story. While the choroid does dissipate heat, much of the heat it dissipates is from the choroid itself. The choroid is pigmented, and this pigment absorbs the light that does not reach the photoreceptors. It is excess heat, not light itself, that is damaging to the retina. In fact, the choroid’s blood flow doesn’t increase in response to light alone.
The role of the choroid in providing energy is important. However, octopus retinal cells are also energy-hungry, and their nutrition is provided quite adequately by blood vessels located behind, not over, the retina.
And here’s an interesting little tidbit on eye evolution. Modern-day vertebrates have one type of photoreceptor cell, insects have a different one. Scientists decided to look at the animal that is the modern-day descendant of the last common ancestor of vertebrates and insects, a marine annelid worm called a ragworm. And what did the scientists find? That the ragworm contains both types of photoreceptors…

Question 14
What one characteristic below do all mammals share?
Five digits per limb- either complete or vestigial
Give birth to live young
Hair at all stages of development
Well-developed sense of sight

The correct answer is Five digits per limb- either complete or vestigial.
Yes, that includes whales that have five digits per flipper, bats that have five digits per wing, horses and antelopes that have vestigial remains of five digits, etc. Five digits isn't the most effective design for many of these creatures- so why should all show the remnants that are easily explained by theorizing that they all descended from a five-toed ancestor? The answer is not "Give birth to live young" because the monotreme mammals, the platypus and echidna, lay eggs.

Marcsana’s response:

5. Evolutionists frequently hop on the poor-design bandwagon before all the facts are in. It is only supposed that these creatures have a weaker design.

My response:
So what are the facts, Marcsana? Note I didn’t state that the design is weaker- but it is suboptimal. Fish don’t have any bones in their flippers; why do whales have five? Goats end up with two usable hooves, horses with one, tapirs with three- why do they all have five digits? Even though some aren’t used? Pandas have five digits, but they need a “thumb” to strip bamboo- why do they have a “thumb” that’s really a radial sesamoid bone and not a true digit? While it makes perfect sense for all mammals to have five digits if a common ancestor did, it doesn’t make any sense at all to create them that way. It certainly doesn’t confer any design advantages.

Question 16:
Why do men and other male mammals have nipples?
Some male mammals give milk
As embryos, all mammals start out phenotypically female
Males need them to produce hormones
There is no reason, they were just created that way
The correct answer is As embryos, all mammals start out phenotypically female.
Only later in development, after the nipples have formed, does a hormonal surge form male sexual structures. This would be an odd thing for a perfect creator to explain, as male nipples are not only useless, they can be dangerous (males can get breast cancer!)

Marcsana’s response:
16. Nipples serve as a sexual stimuli. They have a purpose on men. Furthermore, cancer came after the fall not before.

My response:
Well, there’s a reason for the old saying “as useless as tits on a boar.” Are you seriously stating that nipples on a boar or an elephant or a mouse serve to generate sexual pleasure? Even in men, studies have shown that only about half of males are aroused by nipple stimulation.

If anyone would like more information on the fascinating topic of suboptimal structures, please see my quiz Evidence for Evolution- Unintelligent Design.
There, you'll find many more examples, such as my favorite...humans can't produce vitamin C because the gene needed to do so is broken (most mammals can produce their own vitamin C. ) Well...the gene is broken in the great apes as well- in exactly the same way. So now you know the answer to at least one of the questions on that quiz! :>)

No comments: