In this crazy and progressive world that we have here where monogamy is the established “norm” and medical sciences are advancing at a rapid pace as it has been for many, many decades, we may find that these two things are having humanity bypassing the advantages that natural selection and evolution would provide.
Natural Selection would normally be able to weed out undesirable traits and mutations fairly quickly (speaking in relative evolutionary terms here) by not allowing them to be passed on to future generations. Monogamy and our Advancing Medical Sciences bypasses this evolutionary benefit.
Monogamy ensures that, with birthrates (55% male and 45% female) as they are, just about all males will essentially have a one mate (assuming an even population density) and that each person will have only one choice for a mate, even if that choice is not as good or desirable as they could possibly have or desire.
The top males will have their choice of mates and the less desirable males will have the left-overs. This also means that these less desirable males will all have the opportunity to mate with a less desirable female ensuring that their (collective) less desirable genetics shall be passed on – perpetuating genes that would normally be weeded out due natural selection.
Today’s world with enforced monogamy essentially helps to ensure that “less desirable” mates will be able to find a mate and will be able to pass on their less desirable genes to future generations. This ensures that genetic mutations and abnormalities will be carried on to future generations and it will take much longer for them to be removed from humanity’s gene pool; whereas in cases where natural selection is allowed to run rampant the mates with less desirable traits or abnormalities would have their genes not passed on due to not being able to find a mate, thereby removing defective genes from the gene pool earlier, which allows for a higher quality and healthier humanity sooner than later.
Advanced medical sciences help to ensure that people with defective genes live longer and are more able to find mates; and therefore live longer and be more able to find a mate allowing them to carry on their defective genes to future generations, again, bypassing the advantages of Natural Selection.
People that would normally die off due to a severe genetic disease or would be shunned due to physical deformity or weakness are able to find a cure for their health and physical condition or are able to have the indications or effects of a physical abnormality removed or minimized, and therefore are able to procreate due a longer life span or abnormality minimization.
Advanced medical sciences allow people to live longer and healthier, and are able to hide evidence or minimize the effects of genetic abnormalities. Combined with monogamy’s gift of a higher probability of finding a mate make it much more likely that defective genes will remain in humanity’s gene pool longer instead of being weeded out due to no being able to find a mate.