@BlueSkyKing Why? I don't know. I can't assume that we could even tell the difference. What we think would be the hard way may not be. I don't think anything is obvious about it. Of course I don't even know what the hell we are talking about. If you look at the laryngeal nerve you may draw different conclusions than a creationist would. So why do you think that laryngeal nerve is evidence for evolution? Briefly, the basics. In your own words.
BlueSkyKing [quote]One of my favorite evidences for not intelligent design is the recurrent laryngeal nerve[/quote]
SemmelweisReflex [quote]Why?[/quote]
The recurrent laryngeal nerve (RLN) originates near the top of the brain and connects to the muscles of the larynx (voice box). This nerve allows us to speak and to swallow.
To connect the brain to the larynx, the nerve needs to be 30 centimetres long (at most). In reality, the RLN is more than 90 centimetres long. The RLN travels down the spinal cord all the way to the upper chest. From there, the RLN exits the spinal cord a little below the shoulder blade. The RLN then loops under the aorta (your body’s main artery) and travels back up to the neck, where it finally reaches the larynx (because the RLN intertwines like that with the large heart vessels, surgeons must be very careful not to damage it when they are operating on the heart).
So why is the RLN so messed up?? As always, the answer lies in our evolutionary history. The nerve originated in ancient fish, so all modern vertebrates have it. In fish, the nerve connects the brain to the gills, which were the ancestors of the larynx. However, fish don’t really have necks, their brains are tiny, they don’t have lungs, and their hearts are more like muscular hoses than pumps like ours. Consequently, a fish’s central circulatory system, located mostly in the space behind its gills, is quite different to ours.
In fish, the nerve makes the short trip from the spinal cord to the gills in a predictable and efficient route. Along the way, however, it weaves through some of the major vessels that exit the fish heart, the equivalent of the branching aortas of mammals. This weaving works fine for fish anatomy and allows for a compact and simple arrangement of nerves and vessels in a very tight space. Unfortunately, this paved the way for an anatomical absurdity that would begin to develop as fish evolved into the tetrapods that would eventually give rise to humans.
During the course of vertebrate evolution, the heart began to move farther back as body forms took on a distinct chest and neck. From fish to amphibians to reptiles to mammals, the heart inched farther and farther away from the brain. But the gills did not. The RLN should not have been affected by the changing position of the heart—except that it was intertwined with the vessels. In the slow and gradual evolution from the biology of a fish to the biology of mammal, there was no way for the nerve to magically jump from one side of the aortic arch to the other The RLN got stuck and was forced to grow into a large loop structure in order to travel from the brain to the neck.
(Giraffes, with their long necks, have it even worse that us. Their RLN is 480 centimetres longer than it needs to be!)
@AkioTsukino The nerve starts at the brain, takes a trip around the aorta, and goes back up to the larynx. Does the same thing with giraffes. Smart design.
@AkioTsukino All vertebrates have discs of cartilage that lubricate the joints between the vertebrae in the spinal column. These discs are compressible to absorb shock and strain. They have the consistency of firm rubber and allow the spine to be flexible while remaining strong. In humans, though, these discs can “slip” because they are not inserted in a way that makes sense given our species’ upright posture.
In all vertebrates [i]except humans[/i] the spinal discs are positioned in line with the normal posture of that animal. For example, the spinal columns of fish endure completely different kinds of strain than the spinal columns of mammals. The fish uses its backbone to stiffen its body and then pulls against it in a side-to-side motion in order to swim. But fish don’t have to worry much about gravity and shock absorption since they are suspended in water.
Mammals, however, must use limbs to hold their body weight, and those limbs must attach to the spinal column. Different mammals have different postures and so require different strategies for weight distribution via the spine. In almost all of the tremendously diverse spinal columns found in nature, the spinal discs have adapted to the posture and gait of the animal. But not in ours.
As our ancestors evolved into a more upright posture, the lumbar (lower) area of the vertebral column became sharply curved. It’s that curve in our lower backs that allows us to walk upright, and to move faster than when we walked on a fours. Unfortunately, that rearrangement of our bones wasn’t accompanied by alterations to the spinal discs. Consequently we’re left with a lower back that is kind of, sort of, might be, could be adequate, but definitely not ‘perfect’ (whatever that would be).
Human vertebral discs are in an arrangement that is optimal for knuckle-walkers, not upright walkers. They still do a decent job of lubricating and supporting the spine, but they are much more prone to being pushed out of position than the vertebral discs of other animals. They are structured to resist gravity by pulling the vertebral joints toward the chest, as if humans were on all fours. With our upright posture, however, gravity often pulls them backward or downward, not toward the chest. Over time, this uneven pressure creates protuberances in the cartilage. This is known as a spinal disc herniation or, more commonly, a “slipped disc.”
Spinal disc herniation is unheard of in any primate species except humans.
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In regard to thus evidence, feel free, at any time, to offer a complete, coherent, and consistent explanation that [i]isn’t[/i] the Theory of Evolution by Natural Selection
@AkioTsukino [quote]the best way for it to be?[/quote]
When you inhale through your nostrils, the flow of air branches into four pairs of large chambers tucked in the bones of your face… the nasal sinuses, which are cavities inside our heads. The air comes into contact with mucous membranes… wet and sticky tissue that catches dust and other particles, including bacteria and viruses, so that they don’t reach your lungs.
The mucous membranes produce a slow and steady flow of sticky mucus. This mucus is swept away by tiny, pulsating, hairlike structures called cilia. The mucus drains into several spots and is ultimately swallowed and sent to the stomach (where the acid destroys it).
Sometimes the system gets gummed up, and that can lead to a sinus infection. Bacteria can establish an infection that may spread throughout the sinuses and beyond. Mucus, normally thin and mostly clear, becomes thick, viscous, and dark green when you have an infection.
Have you ever noticed that dogs, cats, and other animals don’t seem to have head colds nearly as often as humans do? Most humans suffer between two and five head colds (also called upper respiratory infections) per year, and these are often accompanied by full-blown sinus infections. For dogs it’s different. Dogs can get sinus infections, which show up as a runny nose, but it’s rare for them. Most dogs will go their whole lives with no major episodes of infection in their nasal sinuses.
In fact, sinus infections are possible but rare in all non-human animals, although they are a little more common in other primates. Why is it so bad for us?
The reason is that our mucous drainage system is a mess. Specifically, the most important drainage-collection pipes are installed near the top of the largest pair of cavities, the maxillary sinuses, located underneath the upper cheeks. Having the drainage-collection point high within these sinuses is a problem because of gravity. While the sinuses behind the forehead and around the eyes can drain downward, the largest and lowest two cavities must drain upward.
Because the mucous collection duct is located at the top of the chamber, gravity cannot help with drainage. This is the reason why sinus infections are so common in humans but unheard of in other animals.
This is why some people with colds and sinus infections can briefly find relief by lying down and tilting their head back. However, the relief is only temporary. Once a bacterial infection takes hold, drainage alone can no longer combat it, and the bacteria must be defeated by the immune system.
What kind of plumber would put a drainpipe anywhere but at the bottom of a basin? Why is the drainage system at the top of the maxillary sinuses instead of below?
The evolutionary history of the human face holds the answer. As primates evolved from earlier mammals, the nasal features underwent a radical change in structure and function. In many mammals, smell is the single most important sense, and the structure of the entire snout optimises the sense of smell. This is why most mammals have elongated snouts... to accommodate huge air-filled cavities full of odour receptors. As our primate ancestors evolved, however, there was less reliance on smell and more reliance on vision, touch, and cognitive abilities. Accordingly, the snout regressed, and the nasal cavities were squashed into a more compact face.
Nowhere are there more differences between humans and nonhuman primates than in the facial bones and skull. Humans have much smaller brows, smaller dental ridges, and flatter, more compact faces. In addition, our sinus cavities are smaller and disconnected from one another, and the drainage ducts are much skinnier… a side effect of making room for our big brains.
This rearrangement produced a suboptimal result that has left us more susceptible to painful sinus infections than any other animal.
@AkioTsukino [quote]the best way for it to be?[/quote]
Unlike other primates, humans walk on two legs (bipedalism). Gorillas, chimps, bonobos and orang-utans amble about using their feet and their knuckles (quadrupedalism). However, moving around on four limbs can be inefficient. On open ground, bipedalism bestows an evolutionary advantage by allowing humans to move much faster than other primates, but that comes at a cost (with evolution, there are no free lunches)
The intestines and other visceral organs are held together with thin sheets of connective tissue called mesenteries. Mesenteries are elastic and act to keep the gut loosely in place. Because we are bipedal, with an upright posture, these thin sheets should be suspended from the top of the abdominal cavity. Instead, they are attached to the back of the abdominal cavity. That makes sense for the other quadrupedal primates, because their gut is then well-supported when they walk on all fours. However, it makes no sense for us… unless we evolved along with the other quadrupedal primates.
Because of the stress of supporting our internal organs from the back, the mesenteries can easily tear, causing internal haemorrhaging and damage to our gut, requiring surgical intervention (this is a common injury in traffic accidents… mainly affecting those stupid enough not to wear a seatbelt). It can also happen to people who sit for long periods of time (drivers, office workers, etc) simply because of the stress and strain of the gut being attached to the back, rather than the top, of the abdominal cavity.
@AkioTsukino [quote]draw different conclusions than a creationist would[/quote]
In regard to the evidence I have offered to you, feel free, at any time, to offer a complete, coherent, and consistent explanation that isn’t the Theory of Evolution by Natural Selection
@AkioTsukino Very small marine organisms, such as plankton, are ideal for showing gradual evolutionary change. There are many billions of them, many with hard parts, and they conveniently fall directly to the seafloor after death, piling up in a continuous sequence of layers. Sampling the layers in order is easy: you can thrust a long tube into the seafloor, pull up a columnar core sample, and read it from bottom to top (our research institutes here in New Zealand do this routinely).
Come to New Zealand and I will show you a two-hundred-meter-long core taken from the ocean floor near New Zealand, presenting an unbroken history of the evolution of the marine foraminiferan [i]Globorotalia conoidea[/i] over an eight-million-year period.
Or you might prefer the eighteen-meter-long core extracted near Antarctica, representing two million years of sediments, showing us, again in an unbroken history, the evolution of the radiolarian [i]Pseudocubus vema[/i]
Or perhaps you’d like to see my personal favourite… a core sample that shows an ancestral plankton species [i]Eucyrtidium calvertense[/i] dividing into two descendants from a common ancestor over 3.5 million years. The new species is [i]Eucyrtidium matuyamai[/i]
@AkioTsukino In regard to the evidence I have offered to you, feel free, at any time, to offer a complete, coherent, and consistent explanation that isn’t the Theory of Evolution by Natural Selection
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In a female mammal there is a pair of tubes along which eggs travel from the ovaries to the uterus. These are called the Fallopian Tubes (salpinges). Sometimes when a human egg is ejected from an ovary it does not make it into the fallopian tube. This is because, quite oddly, the fallopian tube is not actually connected to the ovary. Rather, the opening of the fallopian tube envelops the ovary, like a too-large garden hose resting on a too-small spigot. The two are not actually attached, and sometimes an egg gets squirted out of the ovary and into the abdominal cavity instead of into the fallopian tube.
When this happens, it is usually of no consequence. The egg simply dies after a few days and is resorbed by the peritoneum, the thin wall of highly vascular tissue surrounding the abdominal cavity. No problem.
However, if an egg falls into the abdominal cavity and sperm arrives within a day or so, it might find this egg and fertilise it. The resulting embryo, completely unaware of how far it is from home, begins the process of growth, division, and tunnelling into whatever nearby tissue that it can find, usually the peritoneum but occasionally the outer covering of the large or small intestine, liver, or spleen. This is called an abdominal pregnancy
Abdominal pregnancies pose serious risks. In developing countries, they usually result in the death of the mother. In developed countries, they are easily spotted with ultrasounds and treated with surgical intervention to remove the doomed embryo and repair any damaged tissue or bleeding.
Despite creationists’ laughable claims of an ‘intelligent designer’, abdominal pregnancies are 100% the result of unintelligent design. Any reasonable plumber would have attached the fallopian tube to the ovary, thereby preventing tragic and often fatal mishaps. An ‘intelligent designer’ would never have created the small gap between the human ovary and Fallopian tube, so that an egg must cross this gap before it can travel through the tube and implant in the uterus.
In reality, the gap is a remnant of our fish and reptilian ancestors, who shed eggs directly from the ovary to the outside of their bodies. The Fallopian tube is an imperfect connection because it evolved later as an add-on in mammals.
