The article by Lawrence and Ochman provides a comprehensive analysis of the impact of horizontal genetic transfer on the evolution of the *Escherichia coli* genome. Using the complete sequence of *E. coli* strain MG1655, they identified 755 ORFs (547.8 kb) that were introduced through at least 234 lateral transfer events since the species diverged from *Salmonella* 100 million years ago. The average age of these introduced genes was 14.4 million years, suggesting a transfer rate of 16 kb/Myr/lineage. Despite most acquired genes being deleted, the persistent genes (~18% of the current chromosome) have conferred properties that enable *E. coli* to explore new ecological niches. The authors highlight the importance of horizontal transfer in shaping bacterial genomes, as point mutations alone cannot explain the rapid adaptation of bacteria to new environments. They describe methods to identify horizontally transferred sequences and estimate their age, using the distribution of base composition and codon usage patterns. The study reveals that the segment surrounding the replication terminus of the *E. coli* chromosome has experienced a higher number of horizontal transfer events, likely due to elevated recombination levels. The impact of horizontally transferred DNA is further discussed, emphasizing its role in the diversification and speciation of *E. coli*. The acquisition of novel genes through horizontal transfer has provided *E. coli* with traits such as lactose utilization, citrate utilization, and pathogenicity, which are not present in related nonpathogenic species. The authors conclude that horizontal transfer is a significant driver of bacterial evolution, allowing for the rapid exploitation of new environments and the emergence of new species.The article by Lawrence and Ochman provides a comprehensive analysis of the impact of horizontal genetic transfer on the evolution of the *Escherichia coli* genome. Using the complete sequence of *E. coli* strain MG1655, they identified 755 ORFs (547.8 kb) that were introduced through at least 234 lateral transfer events since the species diverged from *Salmonella* 100 million years ago. The average age of these introduced genes was 14.4 million years, suggesting a transfer rate of 16 kb/Myr/lineage. Despite most acquired genes being deleted, the persistent genes (~18% of the current chromosome) have conferred properties that enable *E. coli* to explore new ecological niches. The authors highlight the importance of horizontal transfer in shaping bacterial genomes, as point mutations alone cannot explain the rapid adaptation of bacteria to new environments. They describe methods to identify horizontally transferred sequences and estimate their age, using the distribution of base composition and codon usage patterns. The study reveals that the segment surrounding the replication terminus of the *E. coli* chromosome has experienced a higher number of horizontal transfer events, likely due to elevated recombination levels. The impact of horizontally transferred DNA is further discussed, emphasizing its role in the diversification and speciation of *E. coli*. The acquisition of novel genes through horizontal transfer has provided *E. coli* with traits such as lactose utilization, citrate utilization, and pathogenicity, which are not present in related nonpathogenic species. The authors conclude that horizontal transfer is a significant driver of bacterial evolution, allowing for the rapid exploitation of new environments and the emergence of new species.