How can I see which author has contributed what in a page

In the top right corner of a protein page, above the Edit button, you can find who last modified a protein entry:

Click on the date to link to the versions archive. Along with a list of all the versions of the page in reverse chronological order, the author and number of words added and deleted are noted. Select two versions you wish to compare:

Then click on "revision comparison" at the top of the page:

Highlighted in green, are the additions made in the later version of the two versions, in red the deletions. If you wish to revert to the earlier version, click on "revert" to the older of the two versions.