自从第一个真核细胞在距今大约40亿年前从原核生物起源以来，原核生物几乎没有表现出要形成更大复杂性的倾向。
相比之下，真核细胞构成所有复杂多细胞生物的基础。所有真核细胞要么有线粒体，要么曾经有但后来失去了，所以线粒体和真核细胞的起源也许是同一事件。
为什么它如此有优势呢？
Nick Lane 和William Martin提出，通过使氧化性磷酸化能在内部膜的很多地方进行，线粒体基因帮助使可以表达出来的基因数量增加了20万倍，同时也使新的蛋白折叠、蛋白互动和调控级联的数量大大增加。（生物谷Bioon.com）
生物谷推荐英文摘要：
Nature doi:10.1038/nature09486
The energetics of genome complexity
Nick Lane1 & William Martin2
All complex life is composed of eukaryotic (nucleated) cells. The eukaryotic cell arose from prokaryotes just once in four billion years, and otherwise prokaryotes show no tendency to evolve greater complexity. Why not? Prokaryotic genome size is constrained by bioenergetics. The endosymbiosis that gave rise to mitochondria restructured the distribution of DNA in relation to bioenergetic membranes, permitting a remarkable 200,000-fold expansion in the number of genes expressed. This vast leap in genomic capacity was strictly dependent on mitochondrial power, and prerequisite to eukaryote complexity: the key innovation en route to multicellular life.
