Structures in galaxies: nature versus nurture. Input from theory and
  simulations
  Galaxies, in particular disc galaxies, contain a number of structures and
substructures with well defined morphological, photometric and kinematic
properties. Considerable theoretical effort has been put into explaining their
formation and evolution, both analytically and with numerical simulations. In
some theories, structures form during the natural evolution of the galaxy, i.e.
they are a result of nature. For others, it is the interaction with other
galaxies, or with the intergalactic medium -- i.e. nurture -- that accounts for
a structure. Either way, the existence and properties of these structures
reveal important information on the underlying potential of the galaxy, i.e. on
the amount and distribution of matter -- including the dark matter -- in it,
and on the evolutionary history of the galaxy. Here, I will briefly review the
various formation scenarios and the respective role of nature and nurture in
the formation, evolution and properties of the main structures and
substructures.
