Indeed, we now know that the proportion of genetic sequences on earth that belongs to visible organisms is negligible. Furthermore, only 15% of the genetic sequences found in the samples from the environment and from feces analyzed in metagenomic studies belong to the three domains of microbes currently recognized in the tree-of-life framework – bacteria, archaea, and eukaryotes.
事实上，我们如今知道地球上属于可见生物体的基因序列所占比例是极为微小的。此外，在环境中采集的样本以及宏基因组（metagenomic）研究分析的微小碎屑中，只有15%的基因序列属于生命树概念框架当前认可的三个微生物类别——细菌，古生菌和真核细胞。而病毒则包含有这些基因序列中的另外15%~30%。