https://en.m.wikipedia.org/wiki/Conway%27s_law
Quoting:
"The law is based on the reasoning that in order for a software module to function, multiple authors must communicate frequently with each other. Therefore, the software interface structure of a system will reflect the social boundaries of the organization(s) that produced it, across which communication is more difficult. "
Was it demonstrated? Well, Google for it.
A link to the original paper can be found here:
http://www.melconway.com/Home/Conways_Law.html
