A truly human-specific gene, not merely a human-specific version of an animal gene or a mammal gene or a primate gene — that is something particularly interesting.

In the cartoon version of evolution that is often employed by critics of the theory, a new protein (B) can arise from an ancestral version (A) by stepwise evolution only if each of the intermediates between A and B are functional in some way (or at least not harmful). This sounds reasonable enough, and it's a good starting point for basic evolutionary reasoning.

It is of course a cliche to state that eukaryotic cells (i.e., cells that are not bacteria) are complex. In the case of an animal, tens of thousands of proteins engage in fantastically elaborate interactions that somehow coax a single cell into generating a unique and magnificent organism.

The Notch signaling pathway is a golden oldie of genetics in two ways.

Consider these not-so-random samples from the animal world: a cockroach, a zebrafish, a mouse. What do these creatures have in common? Left to right: American cockroach (Periplaneta americana), zebrafish (Danio rerio), house mouse (Mus musculus). Cockroach image from Wikimedia Commons, zebrafish and mouse from Wellcome Images. Well, they're all animals and that means they're all eukaryotes, for example. They all have DNA-based genomes.

Recently I was reading a superb review article [doi] on the subject of a famous and important cellular signaling pathway called the Notch pathway.