"He tried law instead but found that insupportably dull and finally managed, more or less by default, to aquire a degree in divinity from Cambridge."

I've asked about default before, but the default thing still isn't clear to me. I've tried to find out by searching net and dictionary. No way.

Could one of you kindly put the "more or less by default" part in other words so I may at last understand?

I think it is meaning "by default of something better". Is that correct?

I often use it to mean "that which you do when you don't have instructions/good reasons to do something else." e.g. I tell my patients to sit up and move around; to lay in bed only when they need to rest and not as their default position.
In this case I get the impression that the divinity degree was not chosen for any specific reason or interest but was what "everyone" studied unless they had a specific interest in another area. I think this was the case historically. In what year is your book set?

Thank you. It then has more or less the meaning I guessed. This is about Darwin from a book where people like me learn a tiny little bit about nearly everything. Long term reading but very entertaining and interesting.