Is it possible that cells have had more than one origin?

The origin of cellular life remains a central question in evolutionary biology. Traditionally, cellular life is assumed to have a single origin, with all cells sharing a Last Universal Common Ancestor (LUCA). This assumption is based on shared features like the genetic code and core translation machinery. However, recent studies suggest that some key cellular processes may not share a common evolutionary origin. For example, DNA replication and lipid biosynthesis show low sequence homology between Bacteria and Archaea. This raises the question of whether cellular organization evolved more than once. Alternative models propose that viruses and progenotes may have played a role in the early diversification of life. These findings challenge the traditional view of cell monophyly and suggest multiple evolutionary pathways.

This study aims to re-evaluate the evidence supporting a single origin for cellular life. It focuses on the assumption that shared features like the genetic code and translation machinery imply a single cellular ancestor. The authors examine whether these features actually support a single origin for all biological systems, including viruses and progenotes. They investigate whether key biochemical pathways are homologous between Bacteria and Archaea. The study also explores whether the concept of LUCA as a cellular entity is still valid. By analyzing the genetic and biochemical evidence, the authors seek to determine if cellular life may have evolved multiple times. This work challenges the traditional view of cell monophyly and proposes alternative evolutionary scenarios. The goal is to stimulate further discussion on the origins of cellular organization.

The study uses a logical and conceptual analysis of cellular characteristics. It evaluates the evidence for a single origin of cells based on shared features like the genetic code. The authors compare the universality of the genetic code with the diversity of cellular organization. They examine the evolutionary relationships between Bacteria, Archaea, and viruses. The study also assesses the homology of key biochemical pathways, such as DNA replication and lipid biosynthesis. Sequence similarity between proteins involved in these pathways is analyzed across Bacteria and Archaea. The authors use this data to question whether these pathways share a common ancestor. The logical framework is used to propose alternative evolutionary scenarios for the origin of cellular life.

The study finds that the genetic code and translation machinery are universal but do not necessarily imply a single origin for cells. These features may instead indicate a single origin for all biological systems, including viruses and progenotes. DNA replication and lipid biosynthesis show low sequence homology between Bacteria and Archaea. The identities of proteins involved in these pathways are too low to suggest common ancestry. This suggests that these pathways may have evolved independently in the two domains of life. The authors argue that this evidence supports the possibility of multiple origins of cellular organization. The concept of LUCA as a cellular entity is challenged, as cellular life may have evolved more than once. The findings suggest that different biological systems, such as viruses and cells, may have originated from distinct progenote populations.

The authors conclude that the evidence for a single origin of cells is not as strong as previously assumed. Shared features like the genetic code may indicate a single origin for all biological systems, not just cells. The low sequence homology in key biochemical pathways between Bacteria and Archaea suggests independent evolution. This challenges the traditional view of LUCA as a cellular entity. The study proposes that different biological systems may have evolved from distinct progenote populations. This implies that cellular organization may have evolved multiple times. The findings suggest that viruses, bacteria, and archaea may have originated independently. The authors emphasize the need to consider alternative evolutionary scenarios for the origin of life.