I do see fitness challenges from internal (genetic — specifically over representation of recessive patterns) and external (environ — caused by technology, overpopulation, etc) both as we are the first species to introduce the ability to externally-protect the ill, weak or genetically maladapted to the age of reproduction therefore expanding recessive combination(s) that could not have persisted before now. Furthermore, we’ve done this in a quickly expanding large populations due to the incredible energy resource of primarily fossil fuels. This topic can lead, sadly, with less complex thinking that is more focused on resource scarcity and control or power, to the idea of eugenics… which are horrible for a number of moral and ethical reasonings but moreover, eugenics actually produces a population more-at-risk of collapse over time.

Environmental pressure(s) are reducing overall human male fertility and social/educational pressures are reducing family size as communities require female workforce production to maintain current living standards. Many believe the human race will hit 11 billion on the planet around 2090–2100 before plateau and then overall population numbers will regress back to whatever carrying capacity the Earth can afford without the massive extra energy from fossil fuels. I do not think we will see 10 billion, personally. I believe we, planetwide, will choose to have less children much more rapidly than the models predict.

We are certainly not the first species to gain a distinct competitive advantage in an environment and have an abundance of energy and food for generations. Albeit, we are the first conscious of that as a species. Most of those species stories end in collapse as the environment changes or the food or energy supply is exhausted. Responding to that threat is the real challenge for human beings, I agree.

Although this topic began with changing jaw formation, skull changes, breathing differences in modern versus humans from just 300 years ago… I believe that the longer term effects from dietary, sleeping and environmental physical stresses in the human population health are just beginning. I’m talking about the overall disease-states caused by five (or more) decades of altered diet, sleep and physical stress/activity. I, like many doctors, hope that Alzheimer's has an actual root single cause (be it genetic, environmental or other) but I’ve suspected for a while that the symptoms we see (on autopsy) are from the decades of these ‘differing’ stresses on modern humans vs. humans from 300 years ago.

Of course, we are living longer. Cancer was rarely diagnosed before the average human lifespan hit 50 years and then by the time it hit 70 years, a lot more cancer got diagnosed. Perhaps Alzheimer's will end up just being age related neural tissue going off the genetic-software program and causing chronic inflammatory changes that are what we see on autopsy. Caring for this population will be a very difficult challenge for our societies.

Time will tell. I have enjoyed our discussion, John. Thank you for the engagement.

~Chris