To be fair, there&#x27;s nothing wrong with exctinction, just as there is nothing wrong with &quot;invasive species&quot;. These things are as old as the hills. A certain amount of genetic turnover is, as you point out, just the fitness function making its judgements.<p>The trouble we have is the <i>rate</i> of extinction and invasion. A typical ecology can support a certain rate of species loss... A single species will be replaced by other organisms that can occupy the same niche. They will fill in the gaps and the same level of biodiversity can be maintained.<p>However these things take time. And if, while the replacement species is adapting to fit the old niche, another several extinctions happens, we start to have problems. Organisms that could&#x27;ve adapted to fill out the niche are themselves under stress. Once you have several key species under stress simultaneously, you run the risk that an entire segment of the food chain... possibly double digit percentages of the metabolic chain, will collapse simultaneously.<p>With a slow enough rate of extinction, you can just keep filling in the holes, but once you cross a certain threshold, you can trigger a regression to a more primordial state. Like desert. You end up with orders of magnitude less complex of an ecology.<p>If think we can get by on a planet with an ecology that is an order of magnitude less complex, with an order of magnitude (or two) fewer species, then none of what I&#x27;m saying is a problem for you.<p>I am scared of dramatically decreasing the number of species just because it seems really hard to predict the effects of that. So I&#x27;d like to delete the species as slowly as possible to mitigate our risk.