New groundbreaking research, published in the esteemed journal Nature, affirms the dominant role of Asgard archaea in the process of eukaryogenesis—the evolutionary origin of complex eukaryotic cells. Scientists have long sought to understand the transition from simple prokaryotic cells to eukaryotes, which encompass all animals, plants, fungi, and other complex life forms. This study utilizes an expanded genomic sampling of Asgard archaea and rigorous phylogenetic analyses to definitively place eukaryotes as a clade nested within the Asgard archaea, identifying them as the closest microbial relatives to all complex life. The findings reveal that a substantial majority of the genes in the Last Eukaryotic Common Ancestor (LECA) can be traced back to Asgard archaea. This suggests that many complex features previously thought to be unique to eukaryotes, such as components of the cytoskeleton and membrane-trafficking machinery, already existed in the ancestral Asgard lineage. The research proposes a model where key aspects of eukaryotic cell organization evolved within the Asgard ancestor. This evolutionary stage was subsequently followed by the crucial endosymbiotic event: the engulfment of an alphaproteobacterium, which then evolved into mitochondria, a defining organelle of eukaryotic cells. This study significantly enriches our understanding of the tree of life, demonstrating that the genetic basis for much of eukaryotic complexity originated from these ancient microbes. It challenges previous models that might have underestimated the pre-existing complexity of the archaeal host. The comprehensive analysis, encompassing a vast collection of archaeal, bacterial, and eukaryotic genome sequences, provides a robust framework for understanding one of life's most pivotal evolutionary transitions.