The first complex cells had genes from a complex mix of species

Our understanding of complex cells, the building blocks of human life, is evolving. Traditionally viewed as a unique branch of the evolutionary tree, recent research reveals that our genome is a remarkable blend of genes from various sources, including bacteria and archaea, alongside those developed within our own lineage. The prevailing theory suggests that the first complex cells emerged from a fusion of archaeal cells and bacteria. This union led to the evolution of mitochondria, organelles that produce energy and still carry remnants of their bacterial ancestry. Over millions of years, many bacterial genes migrated to the nucleus of what we now identify as eukaryotes, intertwining with archaeal genes. However, a new study challenges the simplicity of this narrative. It indicates that the process of gene transfer from bacteria to eukaryotic ancestors was far more intricate than previously thought. While the fundamental idea of a fusion between bacteria and archaea remains valid, the study emphasizes that multiple waves of gene transfer occurred, complicating the evolutionary picture. The journey to this understanding was long and complex. It took a significant amount of time for scientists to classify archaea as a distinct lineage. Furthermore, the initial proponent of the theory that mitochondria originated from bacteria faced skepticism for years before her ideas gained traction. She later proposed that the origins of all complex structures within eukaryotic cells may have followed similar paths, although this is still a matter of debate.