Remember 'analogous' and 'homologous'? Many a college student memorized the difference as applied to the evolution of structures like limbs and wings. Insect wings and bird wings are analogous; bird wings and human arms are homologous. But in modern evolutionary biology, as illuminated by genomics, the two words don't carry enough explanatory clout to deal with the many related genes held in common between species.
Rising to the challenge, molecular biologists adopted 'orthologous' and 'paralogous' to describe the relationships (the words were actually coined more than 30 years ago1). Unfortunately, as the new words began popping up everywhere, the rest of us were left to wonder, "Where did those come from, and what do they mean?!" After overcoming the activation energy of embarrassment, I summoned the courage to ask friends--discreetly of course--who offered sometimes conflicting definitions. One molecular colleague even admitted, "I've been wondering about that myself."
If you are ...
