OK, I hope my question doesn’t get misunderstood, I can see how that could happen.
Just a product of overthinking.
Idea is that we can live fairly easily even with some diseases/disorders which could be-life threatening. Many of these are hereditary.
Since modern medicine increases our survival capabilities, the “weaker” individuals can also survive and have offsprings that could potentially inherit these weaknesses, and as this continues it could perhaps leave nearly all people suffering from such conditions further into future.
Does that sound like a realistic scenario? (Assuming we don’t destroy ourselves along with the environment first…)
Yes absolutely. We’ve already affected our biology and evolution.
Birth control, antibiotics, are examples
Given time, and even greater lifespans, we will have a larger impact on the path of our evolution.
As a thought experiment let’s imagine humans that live for 2,000 years. What does this mean for our adaptability to environmental changes? What does this mean for our fertility?
If nothing else changes, the carrying capacity for new humans will decrease, if the average lifespan goes up to 2,000 years.
From an evolutionary perspective, the question is always what is the current selection pressure? Historically it’s almost always been intelligence plus something else, melanin in the skin, the ability to metabolize lactose into adulthood, etc…