The above, believe it or not, is a mainstream explanation of the gift giving behaviour of the Open Source movement. Trust me I have waded through some stuff to be able to say this with confidence. But I have discovered a twist that will delight the selfish-gene apologists in equal measure with the GPL drafters.
Hacker sex and open source's children
So far we have asserted that the behaviour of the Open Source gift-givers is a variant of a natural social behaviour in a novel context. The givers or authors do gain much kudos I'm sure that is right, but thanks to the GPL they can have offspring!
Open Source code once released into the wild, as it were, is free to be used, copied, adapted, evolve... but most of all persist through time just like successful genes.
The 'genes' of Facebook have many 'parents', as do those of Linux and so on. Developers with high kudos contribute lots of code, most of which will form the backbone of a myriad of offspring. You get the picture. Hackers gain Kudos and thereby enhance their 'reproductive' success... pure high school sociobiology.
Now does any one think that the closed code of a company like Microsoft is going any ware except into oblivion? Who will pick-up and run with the code of CIFS, for example. The only way MS's 'genes' can survive is if they release their code as Open Source soon.
In ten year's time the ancestral progenitors of much open source code will be forgotten but every application will share some of their genes. This can't happen for closed source. From a hacker's view point it's as good as sex.
Paradoxically, a wealthy consumer society famed for its selfishness made it possible for a few with their basic needs more than met to be able to give away things.
That wealth also made it possible for societies to re-arrange themselves back into neo-tribes through social networking and this in turn re-kick-started 'kudos as a driver.
Then the GPL finished the work because it released the code to thrive or perish in the wild.
Evolution will out. Happy birthday Facebook.