What is the driving force behind the evolution of the 14 species of finches on the Galapagos?

I can’t remember the specifics about this…but basically this is what happened…. The islands had really dry weather for a few a seasons, this drier climate killed many seeds of plants before they had a chance to germinate. However, seeds with thicker coatings were better at surviving because the thicker coat allowed for better moisture retention which helped the seeds germinate during the dry period. Hence survival of the fittest. Because the only plants to survive had developed mainly from seeds with thick coats, they had offspring seeds with mainly thick coats.
(Think about humans with brown hair and eyes…most likely…they will have more children with the same dark colouring)
Therefore there was a higher proportion of seeds in the population with thick coats, then there had been before the dry years had started.
(Back to people with dark colouring…imagine the ozone degraded and people are exposed to higher levels of UV radiation. Dark people have more pigment aka melanin which also acts as a natural sunscreen, therefore light people are getting cancer, their kids are getting cancer and they are not having many healthy offspring. The darker people keep having dark children with natural sunscreens that enable them to survive the new high UV environment.) Now back to finches….

Finches eat seeds and they use their beaks to crack open the outer coating. Finches with larger more robust beaks were capable of cracking open the thicker seed coats. The finches with smaller beaks were able to crack open the thinner seed coats but not the thick seeds. And because thick seeds became more abundant, finches with larger beaks had more to eat and thus survived to have offspring. And because the finches most likely to survive had big beaks, their offspring are likely to have large beaks…this continues for generations until a large proportion of the finch population has large beaks. It was these observations that led to Darwin’s theories of natural selection.
So basically natural selection is driven by the ever-changing environment and natural selection is the driving force behind evolution.