As new, powerful methods for studying brains became available in the 1970’s, a doctrine developed that held that, apart from size, which is highly variable across species, the organization of the cerebral cortex does not vary in important respects across species. この文章の”a doctrine developed that held that”という部分ですが、held that が持つ意味は何なのでしょうか？無くても良いよな気がするのですが…. また、それぞれのthatがどこを指すのかいまいち分かりません。どなたか、教えて頂けると幸いです。
英語
