We often imagine our complex cells as a solitary branch on the tree of life. But it turns out that far from being a distinct entity, our genome is a fascinating mix of genes from bacteria and archaea – a true genetic melting pot.

It was once thought that the first complex cells emerged when an ancient bacterium merged with an archaeal cell. The bacteria eventually evolved into mitochondria, the powerhouse of eukaryotic cells, which still retain some of their original genetic material. Over time, other bacterial genes moved to the nucleus, intermingling with archaeal genes.

However, a recent study reveals that this picture is more complex than initially thought. There were multiple waves of gene transfers from bacteria into eukaryotic cells. While the merger between archaea and bacteria was pivotal, it wasn't the only event shaping our genetic makeup. This means that the big merger theory is still correct but incomplete.

The journey to this understanding has been long and winding. For a while, scientists struggled to recognize archaea as a distinct lineage, and the idea of mitochondria being engulfed by another cell was met with skepticism for years before gaining acceptance. The next step will be to unravel exactly how these gene transfers occurred and what impact they had on our cellular evolution.