How to rewrite this long sentence?
The original: John Dewey has said in all seriousness the part played by custom in shaping the behavior of the individual as over against any way in which he can affect traditional custom, is as the proportion of the total vocabulary of his mother tongue over against those words of his own baby talk that are taken up into the vernacular of his family.

The rewritten sentence is required to begin like this: The proportion of the total vocabulary of his mother tongue over against those words of his own baby talk that are taken up into the vernacular of his family.....

Question

How to rewrite this long sentence?
The original: John Dewey has said in all seriousness the part played by custom in shaping the behavior of the individual as over against any way in which he can affect traditional custom, is as the proportion of the total vocabulary of his mother tongue over against those words of his own baby talk that are taken up into the vernacular of his family.

The rewritten sentence is required to begin like this: The proportion of the total vocabulary of his mother tongue over against those words of his own baby talk that are taken up into the vernacular of his family.....

Answer

The proportion of the total vocabulary of his mother tongue, in contrast to the words of his own baby talk that are incorporated into the vernacular of his family, is, in all seriousness, as emphasized by John Dewey, the primary factor shaping the behavior of the individual, rather than any influence he may exert on traditional custom.