human
Moreover, such specialities of structure as are due to specialities of function, are usually entangled with specialities which are, or may be, due to selection, natural or artificial. In most cases it is impossible to say that a structural peculiarity which seems to have arisen in offspring from a functional peculiarity in a parent, is wholly independent of some congenital peculiarity of structure in the parent, whence this functional peculiarity arose. We are restricted to cases with which natural or artificial selection can have had nothing to do, and such cases are difficult to find. Some, however, may be noted.
gpt
; its leaves may become hairy, its stem woody, its branches drooping.
human
These are modifications of structure consequent on modifications of function that have been produced by modifications in the actions of external forces. And as these modifications reappear in succeeding generations, we have, in them, examples of functionally-established variations that are hereditarily transmitted.