https://phys.org/news/2020-04-reveals-life-earliest-evolution-complicated.html New study reveals life's earliest evolution was more complicated than previously suspected: Biologists have long hoped to understand the nature of the earliest living organisms on Earth. If they could, they might then be able to say something about how, when, and where life arose on Earth, and perhaps by extension, whether life is common in the Universe. Previous studies have suggested this information can be obtained by comparing the genes present in modern organisms. New research indicates that only limited information can be derived using this approach. Biologists classify all living organisms into three major groups they call 'domains.' Two of these domains—the Bacteria and the Archaebacteria—consist of single-celled organisms, while the third—the Eukaryota—includes most of the larger, multicellular organisms we are all familiar with: fungi, plants and animals including ourselves. Of the three domains, the Eukaryota almost certainly evolved the most recently, but questions remain about which of the two single-celled domains arose first in the history of life. Over forty years ago, American biologists Carl Woese and George Fox suggested that these two domains both emerged from a more primitive organism or group of organisms scientists now call LUCA, or the Last Universal Common Ancestor. Scientists would love to be able to say something concrete about what LUCA was like, what types of environment it lived in, and how it made its living. more at link..... the paper: https://academic.oup.com/mbe/article/doi/10.1093/molbev/msaa089/5818498 Abstract Comparative genomics and molecular phylogenetics are foundational for understanding biological evolution. Although many studies have been made with the aim of understanding the genomic contents of early life, uncertainty remains. A study by Weiss et al. (2016) identified a number of protein families in the last universal common ancestor of archaea and bacteria (LUCA) which were not found in previous works. Here we report new research that suggests the clustering approaches used in this previous study under-sampled protein families, resulting in incomplete phylogenetic trees which do not reflect protein family evolution. Phylogenetic analysis of protein families which include more sequence homologs rejects a simple LUCA hypothesis based on phylogenetic separation of the bacterial and archaeal domains for a majority of the previously identified LUCA proteins (∼82%). To supplement limitations of phylogenetic inference derived from incompletely populated orthologous groups, and to test the hypothesis of a period of rapid evolution preceding the separation of the domains, we compared phylogenetic distances both within, and between domains, for thousands of orthologous groups. We find a substantial diversity of interdomain vs. intradomain branch lengths, even among protein families which exhibit a single domain separating branch and are thought to be associated with the LUCA. Additionally, phylogenetic trees with long interdomain branches relative to intradomain branches are enriched in information categories of protein families in comparison to those associated with metabolic functions. These results provide a new view of protein family evolution, and temper claims about the phenotype and habitat of the LUCA.