There are lot of unstated assumptions involved here. Let’s assume that the tendency to take the anti-aging drug is hereditary—so we’re really discussing whether or not selection will favour the gene for doing this. If the mortals and “immortals” (who actually die after ca. 1000 years) are not reproductively isolated, then it seems quite clear that the gene for taking the drug will be favoured by selection. If one assumes reproductive isolation (as the post seems to), perhaps for social reasons, but that the two groups compete for resources, then the immortal group loses out only if their higher reproductive capacity is outweighed by worse adaptation to changing circumstances. Whether the “immortals” would be less-well adapted will depend on selection effects within that group—if the young immortals out-compete the older immortals, then they adapt just as fast as the mortals. I think you would have a difficult (but maybe not impossible) time finding values for the various within and between group selection effects that would produce a rapid-adaptation advantage for the mortals that would outweigh the huge reproductive advantage of the immortals.
The whole scenario seems rather far from reality to me—talking about evolution implies selection—ie, death or infertility. Assuming the anti-aging drug does not directly affect fertility, I think one can assume that any behavioural trait of low fertility among the immortals will be strongly selected against, after which we’re in the Malthusian state in which the “immortals” often die early from starvation. So the average age when they have children may not be so high after all...
Plus, of course, the scenario assumes a world-changing innovation of an anti-aging drug, but no other world-changing innovations (AI, space travel, …?) that would render the whole discussion irrelevant.
I think I get what you mean by “They have everything the mortals have, plus more” now. The key part is the “200 children” which is of course not sustainable and the answer you and OP have depends on the implicit assumptions of how that is handled.
There are lot of unstated assumptions involved here. Let’s assume that the tendency to take the anti-aging drug is hereditary—so we’re really discussing whether or not selection will favour the gene for doing this. If the mortals and “immortals” (who actually die after ca. 1000 years) are not reproductively isolated, then it seems quite clear that the gene for taking the drug will be favoured by selection. If one assumes reproductive isolation (as the post seems to), perhaps for social reasons, but that the two groups compete for resources, then the immortal group loses out only if their higher reproductive capacity is outweighed by worse adaptation to changing circumstances. Whether the “immortals” would be less-well adapted will depend on selection effects within that group—if the young immortals out-compete the older immortals, then they adapt just as fast as the mortals. I think you would have a difficult (but maybe not impossible) time finding values for the various within and between group selection effects that would produce a rapid-adaptation advantage for the mortals that would outweigh the huge reproductive advantage of the immortals.
The whole scenario seems rather far from reality to me—talking about evolution implies selection—ie, death or infertility. Assuming the anti-aging drug does not directly affect fertility, I think one can assume that any behavioural trait of low fertility among the immortals will be strongly selected against, after which we’re in the Malthusian state in which the “immortals” often die early from starvation. So the average age when they have children may not be so high after all...
Plus, of course, the scenario assumes a world-changing innovation of an anti-aging drug, but no other world-changing innovations (AI, space travel, …?) that would render the whole discussion irrelevant.
I think I get what you mean by “They have everything the mortals have, plus more” now. The key part is the “200 children” which is of course not sustainable and the answer you and OP have depends on the implicit assumptions of how that is handled.