Figure 4.

A small step for a molecule, but a big step for safety. The DNA world and the XNA world would be able to interact on the level of whole organisms (e.g., providing nutrients, capturing CO₂, detecting environmental pollutants) but would not able to exchange genetic material through horizontal gene transfer or via sexual reproduction. Therefore, it acts as a genetic firewall, but not as a biological firewall. In contrast to the natural world, the XNA world is completely dependent on external supply of essential biochemical building blocks that cannot be synthesized either by XNA or DNA organisms. Any “escape” of a xeno-organism out of the direct control of humans would automatically lead to death.