Airborne toxins have to be pretty small molecules, to be volatile, and there are only so many of those. For nerve gases, a water or oil mist can be used as a carrier, to increase the range of viable toxins, but for living creature to do that is a recipe for dehydration.
Nor are any of these toxins stable against sunlight and free oxygen. You could have patches of marsh where the plants gas every passing animal, getting extra fertiliser, but hardly an entire planet. It's simpler to let the humans avoid the poison marshes - apart from the occasional human sacrifice.
Once the precursors have left, the human population will evolve greater tolerance for the local toxins, to the extent that it can, but it will do this through successive point mutations, modifying existing enzymes - giving cellular repair a slightly higher priority and further fine-tuning the liver - and every cell would have precursor organelles, giving extra protection. This is not the kind of selective pressure that causes speciation.
Humans can't evolve a significantly lower need for the various minerals and vitamins. Too much relies on the availability of the minerals - take the iron out of hemoglobin, and it becomes useless. Making the vitamins ourselves would require evolving whole new enzymes, which is too slow to work.
For vitamins, the necessary enzymes could be included in the precursor organelles. For metals, the sun isn't that much richer in metals than its neighbours. The range of metal concentrations on earth is considerably greater Similarly, any world with plate tectonics will have regions where the iron has been concentrated to typical terran levels. Thus, the humans will be fine, even without a fruit of life, provided they stick to areas with the right kind of soil.
Organelles don't eat each other - plants have both mitochondria and chloroplasts, and neither gets eaten. If they're well designed, the precursor organelles will behave themselves. Like mitochondria and chloroplasts, they will only reproduce when their host cell does. They will never cross a cell wall, never run amok.
Terran life has solved all the problems with handling organelles, at least twice. The precursors need only copy the solutions, not a particularly challenging task, compared with all the other things they're doing.
Note: building alien worlds is frequently discussed in rec.arts.sf.science. Looking at the Google archives for that newsgroup should be useful, and you can always post questions in the group itself.
Nor are any of these toxins stable against sunlight and free oxygen. You could have patches of marsh where the plants gas every passing animal, getting extra fertiliser, but hardly an entire planet. It's simpler to let the humans avoid the poison marshes - apart from the occasional human sacrifice.
Once the precursors have left, the human population will evolve greater tolerance for the local toxins, to the extent that it can, but it will do this through successive point mutations, modifying existing enzymes - giving cellular repair a slightly higher priority and further fine-tuning the liver - and every cell would have precursor organelles, giving extra protection. This is not the kind of selective pressure that causes speciation.
Humans can't evolve a significantly lower need for the various minerals and vitamins. Too much relies on the availability of the minerals - take the iron out of hemoglobin, and it becomes useless. Making the vitamins ourselves would require evolving whole new enzymes, which is too slow to work.
For vitamins, the necessary enzymes could be included in the precursor organelles. For metals, the sun isn't that much richer in metals than its neighbours. The range of metal concentrations on earth is considerably greater Similarly, any world with plate tectonics will have regions where the iron has been concentrated to typical terran levels. Thus, the humans will be fine, even without a fruit of life, provided they stick to areas with the right kind of soil.
Organelles don't eat each other - plants have both mitochondria and chloroplasts, and neither gets eaten. If they're well designed, the precursor organelles will behave themselves. Like mitochondria and chloroplasts, they will only reproduce when their host cell does. They will never cross a cell wall, never run amok.
Terran life has solved all the problems with handling organelles, at least twice. The precursors need only copy the solutions, not a particularly challenging task, compared with all the other things they're doing.
Note: building alien worlds is frequently discussed in rec.arts.sf.science. Looking at the Google archives for that newsgroup should be useful, and you can always post questions in the group itself.