i learned about ecto-meso-endo- morphs when i was a child at a psychiatric school. i found a book in my doctors library that i took to read.
it said that there was a scale of 1-7 for each of the somatotypes.
it said that every person contains all 3 somatotypes, and each somatotype is given a value from 1 to 7 as ascribed to an individual.
the score was rated as ectomorphy(1-7) then mesomorphy (1-7) and then endomorphy (1-7)
so an inherently skinny person with no muscle or fat would be a 7,1,1. (7 ecto, 1 meso, 1 endo)
a huge muscle man with not an ounce of fat on him and with big fat bones would be a 1,7,1. (1 ecto, 7 meso, 1 endo)
a person who is obese and is all flab, but has thin bones and no muscle mass maybe a 1,1,7.
there was a psychological attribute ascribed to each of the 3 somatotypes in the book.
apparently....
ectomorphs: are nervous and edgy. they panic easily and they are prone to paranoia and suspicion. they are usually very guarded.
mesomorphs: are impulsive and rash. they are passionate and lose their tempers easily. they attempt to dominate and strive to control. they think about sex often.
endomorphs: are happy and jocular people. they are content with indulgence. they are the most humerous and relaxed of all the body types.
that is what the book said (over many pages) in a very condensed way.
my body type is about a 3-3-3 given that basis for my understanding which is almost certainly outdated.