The Unfinished Reconstructed Nature of the Last Universal Common Ancestor

Abstract

The ultimate consequence of Darwin's theory of common descent implies that all life on earth descends ultimately from a common ancestor. Biochemistry and molecular biology now provide sufficient evidence of shared ancestry of all extant life forms. However, the nature of the Last Universal Common Ancestor (LUCA) has been a topic of much debate over the years. This review offers a historical perspective on different attempts to infer LUCA's nature, exploring the debate surrounding its complexity. We further examine how different methodologies identify sets of ancient protein that exhibit only partial overlap. For example, different bioinformatic approaches have identified distinct protein subunits from the ATP synthetase identified as potentially inherited from LUCA. Additionally, we discuss how detailed molecular evolutionary analysis of reverse gyrase has modified previous inferences about an hyperthermophilic LUCA based mainly on automatic bioinformatic pipelines. We conclude by emphasizing the importance of developing a database dedicated to studying genes and proteins traceable back to LUCA and earlier stages of cellular evolution. Such a database would house the most ancient genes on earth.

Keywords: Astrobiology; Comparative genomics; Early evolution of life on earth.

Fig. 1

Different studies assign varying number of proteins to LUCA. This variation stems from differences in the genome sets and methodologies employed by each study. Some of these studies suggest that LUCA possessed a complexity comparable to extant prokaryotes. Conversely, others propose a simpler entity, more akin to progenotes and closer to the origin of life. It is important to note that the list of studies is not compressive

Fig. 2

Structure and protein subunits of ATP synthase from F- and A/V-types. Figure based on Mahendrarajah et al. (2023)