1. Humans have the highest perinatal mortality rate of any of the great apes. Without good medical care, the commonest cause of death in Homo sapiens is child-birth. In the other great apes, perinatal death for mothers and babies is a rarity.
During our evolution, a large brain, giving a large fetal head, was such an advantage that the benefits outweighed the disadvantage of loss of genes due to high infant mortality. The same applies to an upright gait, which led to a curved birth canal as the pelvis was adapted. A large fetal head being expelled through a curved birth canal is the reason human birth is a prolonged and exhausting process for the mother and the basic cause of perinatal death for both mother and baby. Evolution is driven by selecting for whichever group of genes results in more surviving descendants in the gene pool with no regard to what happens to individuals.
2. Humans suffer from vertebral disc problems, especially in later life.
As an upright gait evolved, our spines needed to develop two curves not normally found in other vertebrate animals. We have evolved a curve in the lumbar region to bring our upper body into an upright position with our thorax and upper limbs above our pelvis to reduce strain on our back muscles. We have also evolved a curve in our cervical vertebrae to bring our face into a forward-facing position and to balance our large skull efficiently. Both these adaptations are incomplete and cause the discs between the vertebrae to herniate and become displaced but usually in later life, after we have passed on our genes to the next generation, so there is only weak advantage to our genes in correcting these defects.
3. Humans suffer from arthritic joint problems, especially in later life.
Arthritis is the result of wear and an auto-immune response in which we produce antibodies to our own tissues. This is normally only a problem for individuals in later life, after the genes have been passed on to the next generation so there is only weak selection pressure towards elimination of these traits. At the same time, as humans domesticated more species we became more exposed to the diseases they carry so our immune systems needed to become more responsive. This has led to an over-eager immune system. One recent piece of research has suggested that we have inherited some of our immune responses from interbreeding with Homo neanderthalensis. These gave us such an advantage in early life that they spread throughout the H. sapiens gene pool regardless of the problems they cause us later on.
4. Humans have an increasing chance of dying as they age from degenerative diseases, including circulatory problems leading to strokes and myocardial infarction, cancers, respiratory problems, loss of vision and hearing, and dementia.
Again, all these problems tend to develop in later life often long after we have passed our genes on to the next generation. Eliminating them makes very little, if any, difference to the survival of our genes in our descendants, so there is weak or no evolutionary pressure to correct these defects.
5. Some humans carry a defective gene for production of haemoglobin and people who inherit this gene from both parents have a condition called sickle-cell anaemia in which the oxygen carrying capacity of their blood is impaired. Left without treatment, these individuals have a low life expectancy and a reduced probability of producing descendants.
One would expect the defective gene to be eliminated as carriers have a reduced chance of producing descendants, and indeed, throughout much of the world, the incidence of this defective gene in the indigenous population is very low. However, carriers of one normal gene for haemoglobin, and one defective gene have a greater resistance to the parasite carried by mosquitoes which causes malaria, giving these individuals a slightly improved chance of reproduction in areas of the world where malaria is endemic or was endemic in recent history, which correspond to areas where the anopheles mosquito is or was recently endemic.
In the presence of anopheles mosquito, evolutionary pressure ensures the survival of an otherwise harmful mutation.
6. The vertebrate eye has a 'blind spot' caused by the nerves from the retina being wired the wrong way round and having to pass through the retina at a point where there are no light receptors. This has meant our brains have had to evolve compensatory mechanisms for infilling the missing information using sometimes invalid assumptions. To demonstrate this, draw a coloured spot on a sheet of white paper and draw a cross about 3 inches from it. Close one eye and move the sheet of paper closer whilst staring at the cross. The black spot will disappear. Your brain has infilled by assuming, in the absence of other evidence, that the sheet of paper is uniformly white.
As the eye evolved the wiring of the nerves became fixed early on. Such were the advantages of even this degree of environmental awareness that the genes for it spread throughout the gene pool and the eye continued to evolve to its present form, complete with its inefficient wiring. Since de-evolving would have given a distinct disadvantage, any tendency to do so, in order to correct this problem would have been selected against. Evolution is utilitarian, directed only by environmental selection and improved survivability and lacks any capacity to intelligently correct for inefficiencies by scrapping a design and starting again.
7. Human eyes have a much poorer acuity than many other vertebrate eyes of essentially the same design. An eagle or a falcon can see detail from a mile away that we might have difficulty seeing at the distance of a few yards.
There is no special advantage in humans being able to see with any greater degree of acuity because, given our lifestyle, we do not need it. For raptors like eagles and falcons however, it can make the difference between eating or starving so the evolutionary pressure has been much greater for them than for us, and the investment in the additional density of receptors in the retina, and in the processing power in their brains, has paid off in terms of gene survival. In humans, there would be no return on this investment.
All of these defects and imperfections can be understood perfectly well with evolution by natural selection. None of them make any sense at all as the product of intelligent design.
Manifestly, the human body was not intelligently designed but is the product of an undirrected, utilitarian process of gradual adaptation which retains and passes on only those characteristics which give a net advantage to the genes carried in terms of their frequency in the gene pool.
One thing is for sure; there is no intelligence behind the design of the human body. (Tweet this)