Life has evolved on earth over hundreds of millions of years. From the
earliest molecules capable of self replication to virus to bacteria, the
complexity of the structures has increased, culminating in the form of
mankind. During this process some mechanisms have been conserved
i.e. RNA/DNA machinery.
Also can be detected, in advanced
species, the remnants of primitive bacteria to bacteria
chemical [quorum sensing] communication. This 'talk' controls
and regulates bacterial colony growth and reproduction.
In higher life forms, such as insects and humans,
this has evolved into an antimicrobial peptide defense
against pathogens or as toxins against predators
as in scorpion tail venom, or, as in frog skins.
Species differ in their pathogen
susceptibility and in the amino acid structure of
the Anti Microbial Peptides that they produce.