. I think that bivalves have evolved to have smaller head regions because they have also evolved to have bigger shells or valves than cephalopod
Schemas refers to a cognitive frame work which help humans to organize and give interpretations to information obtained both from within and from the external enviroment. Schema guide human cognitive processes and behaviour. Schema helps in structuring our memories by acting as a glue which hold all the information we have gathered together. Shcema is used in recognizing new experience and in relating it with old experiences. Schema affects humans' perception, encoding, memory recall, etc.
Any change in allele frequencies in a gene pool is a mutation