Fig. 1

Elements of the hierarchy of life explained by ETI theory (left panel, adapted from Michod et al. 2022) versus levels of organization as commonly introduced in biology textbooks and instructional materials (right panel). ETI theory explicitly addresses six levels in the hierarchy of life: molecular replicators or genes to genomes in cells, prokaryotic cells to eukaryotic cells, single celled organisms to multicellular organisms, and from multicellular organisms to eusocial societies as seen in social insects such as ants and bees. The levels of organization typically introduced in biology textbooks are molecules, cells, tissues, organs, organ systems, and organisms. In addition, levels above the organism are often included in textbooks, such as ecological communities and ecosystems