This product is quite unique in the fact that it shows a GM (or Mutant lord if you prefer) how a possible new species and sub species can evolve over numerous generations from a simple avian like the house sparrow into twenty different but related creatures.
Several long essays delve into the Family Tree concept, the mutant herd concept and finally accelerated evolution, giving any possible designer of new family trees basic guidelines on how to take one creature and literally evolve it into a wide, varied and complex species of distantly related by widely different creatures.
Using four different base creatures, Derek Holland was able to come up with over one hundred variants of these creatures. Some of the variants turned out to be evolutionary dead ends due to mutations, while others thrived quite well in the post apocalyptic world.
Finally, the book included a small number of new mutations to go with the creatures.
This book, just from the concept alone, would be well worth picking up.
[5 of 5 Stars!]