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Eukaryotes are significant because they represent a singularity in the history of life on Earth, arising once about 2 billion years ago. This event gave rise to all complex life, despite bacteria and archaea having a greater genetic repertoire.

The adaptation of cells to internal selection pressures, rather than external environments, may explain why single-celled algae and complex multicellular organisms share similar cellular structures.

Bacterial evolution is fascinating because they maintain small genomes but have access to a large pan genome. For example, an E. coli cell might have 3,000 to 4,000 genes but access to 30,000 to 40,000 genes. This allows them to adapt by borrowing genes from other strains, which is crucial for survival in different environments.

The emergence of eukaryotes is seen as a major bottleneck in the development of complex life. Despite the vast number of planets that could potentially give rise to eukaryotes, it seems this event is incredibly rare, with Earth being a unique example.

Despite the vast number of planets, the unique development of eukaryotes on Earth suggests that while other methods of achieving complexity might exist, they are not easily realized in nature.