Background
I just noticed that the whole commit history in my repo doubles.
For reference, I am the sole contributor, and this is a private repository.
It will appear as if there are two members, because I have an old account whose information was still git config --global user.emailon one of my computers.
Doubling happened after I cloned a project and started working with it from another computer.
Excerpt from git log:
commit 76cd0efa307e501abfe13cd907957e4dcff7e75e
Author: myaccount <account1@gmail.com>
Date: Mon Mar 21 18:58:39 2016 +0100
FEATURE - Add VideoNotFoundException.
commit 0430ef9dc5d3baa2189ba1c18b4bedb9d2940e51
Author: myaccount <account2@gmail.com>
Date: Mon Mar 21 18:58:39 2016 +0100
FEATURE - Add VideoNotFoundException.
commit 94e7221e472e29119c9e4fe48944cd4d7528e207
Author: myaccount <account1@gmail.com>
Date: Mon Mar 21 18:41:11 2016 +0100
FEATURE - Add previous/next video links to video view.
commit 8b26a51b84d4fb3ae72eefe2834649ff8bc8b7ce
Author: myaccount <account2@gmail.com>
Date: Mon Mar 21 18:41:11 2016 +0100
FEATURE - Add previous/next video links to video view.
commit 7f9b3b6f214e445918d509d7f9377d3d7ce875da
Author: myaccount <account1@gmail.com>
Date: Tue Mar 15 17:05:46 2016 +0100
CLEANUP - Remove unused code/uses.
commit c83fa2c238d1437c967b40d6e807c2567eb7572d
Author: myaccount <account2@gmail.com>
Date: Tue Mar 15 17:05:46 2016 +0100
CLEANUP - Remove unused code/uses.
The repository now has 234 commits, of which about half are valid, real commits.
This is also reflected on GitHub:

git log --graph --decorate --oneline --all however does NOT reflect this.
* 303bbfe (HEAD, origin/master, origin/HEAD, master) MERGE
|\
| * b8052ce REFACTOR - Refactor front page content for maintainability.
| * b5907b2 VISUAL - Improve front page mobile view.
| * 0430ef9 FEATURE - Add VideoNotFoundException.
| * 8b26a51 FEATURE - Add previous/next video links to video view.
| * c83fa2c CLEANUP - Remove unused code/uses.
| * 9e82b8f BUGFIX - Fix redirecting /login to front page.
| * 491b88e BUGFIX - Redirecting old playlist and video links to new ones. WIP: Code duplication!
| * a7da158 Merge branch 'master' of https://github.com/alrasch/UDLv2
| |\
| | * a3bfe1b BUGFIX - Fix 500 error on 404 page.
| * | 258d2e9 BUGFIX - Redirecting old URLs to new ones.
| |/
| * 4426681 FEATURE - Add more UDL logo assets.
| * 7d15c7c FEATURE - Add custom 404 page.
| * 6fbb5dd FEATURE - Add 'forgot password' function.
| * 92dd4c8 VISUAL - Fix video view layout.
| * 8a7decb VISUAL - Scale UDL logo to 75% on front page.
| * 0900fbc VISUAL - Rearrange discipline view layout.
| * 1ba38c8 VISUAL - Scale UDL logo on playlist view down to 75%.
| * eef7cd1 VISUAL - Fix playlist view layout.
| * b7fa6cb Made sidebar space on front page.
| * ace9fb6 COSMETIC - Logo on front page and navbar. Rounder buttons.
| * bbf12b3 Add MathJax LaTeX sitewide.
| * 6629128 Customize register form and add email activation.
| * 27f7114 FEATURE - Add basic search to navbar.
My attempts
, , . git rebase -i HEAD~n, , .
reset ( )? ( , GitHub.)
, , , . .
, git . , , git rebase, pick/squash.