redredred · M
I respect Sagan but I don’t need his insight to know the human spine was not designed by a perfect being. A year one engineering student could do a better job. TBH, a year one art major could do a better job. Also, what’s up with human childbirth? The female pelvis ( whole admirable in many respects) is barely up to the job. A descent designer would make a newborns head smaller and then grow, like every other part of its body.
newjaninev2 · 56-60, F
@redredred The optimal gestation period for humans is ten months but by then the head would be so large that most deliveries would be life-threatening.
The down-side of the earlier delivery is that in humans the lungs are the last organs to develop which is why premature births experience respiratory crises and even full-term births can face difficulties.
The down-side of the earlier delivery is that in humans the lungs are the last organs to develop which is why premature births experience respiratory crises and even full-term births can face difficulties.
newjaninev2 · 56-60, F
@redredred 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 except humans 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.
In all vertebrates except humans 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.