As life has diversified over billions of years, so have the ways of extracting a living by exploiting other species. Indeed, no multicellular eukaryotic organism is capable of surviving and reproducing using only its nuclear genes and the gene products it makes. Species coopt the genomes of other species by forming mutualistic, but inherently selfish, alliances. You can grasp the central importance of mutualistic associations in the diversification of life through a simple thought experiment. Try toimagine a plant that can survive and reproduce in a real ecosystem without using, in addition to its nuclear genome, most of the following: a mitochondrial genome (to convert energy); a chloroplast genome (to regulate photosynthesis); one or more mycorrhizal fungal genomes (to improve nutrient and water uptake); the genomes of pollinators (to assist in reproduction); and the genomes of a few birds, mammals, or ants (to move seeds around the ecosystem). Each plant is part of a complex web of interactingmutualists.
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