1.   For just the same reason, it is vanishingly improbable that exactly the same evolutionary pathway should ever be travelled twice.

2.   These results therefore support the idea that common evolutionary pathways were involved in the formation of this branch of the MHC gene family.

3.   Ratchets could help ove life along its evolutionary pathways toward greater complexity.

4.   The explanatory notes on the evolutionary pathway are somewhat more scientific.