Q:

What is this English doing in the middle of my Japanese?

Note: I understand this question is on the edge of being off topic. I'll accept the community assessement if enough people feel that is the case.
I'm reading 脳{のう}は0.1秒{びょう}で恋{こい}をする by 茂木{もぎ}健一郎{けんいちろう}, and out of the blue, there's an English word right in the middle of a sentence:

The sentence reads 人生{じんせい}は「偶有性{ぐうゆうせい}」(contingency)に満{み}ちています。 I think I basically understand it, in that it says life is full of contingencies.
My question, though, is why is this English word here? The book is written by and for Japanese. The way the word is offered, it looks as though it is a clarification of 偶有性{ぐうゆうせい}, where 偶有{ぐうゆう} means having an accident, and 性{せい} means the suffix ~ness, so I guess it's supposed to approximate the word "contingencies".
I just don't get how this would help a Japanese person reading the book? Does Mogi San expect that a Japanese person who doesn't know 偶有性{ぐうゆうせい} would be helped by knowing that it meant "contingencies"? That doesn't seem very likely to me.
I appreciated it, because it helped me understand what he meant, but I don't think this is for the benefit of Japanese learners.
What is going on here?

A:

Technical subjects usually have a large English-speaking community, and theses and books on that subject are often published in English (or some other international language, but you probably get a wider readership by publishing in English).
It's important to know the English technical terms so you can understand those books and theses, so even when reading a Japanese technical book that introduces its terms in Japanese, it will often include the corresponding English terms in parentheses so that you're not completely confused when you try to read foreign material on the subject.
Whether or not this particular sentence is actually from a technical work or field, and even if you are never likely to need to look it up anywhere else, the inclusion of an English word here reminds the reader of that kind of technical text, which does two things:

emphasizes "this is an important word to this discussion" (so important you'd want to learn it in English too)
creates a feeling of "this is a scientific explanation", and implies the presence of other information published elsewhere on the same subject that corroborates the statement 

Looking on Amazon,  the cover of this book has a subtitle of 「『赤い糸』の科学」 on it, so it seems to fit the context.

