Single first author vs co-first author - what difference does it make?

Question

I have a little dilemma to resolve. I am about to submit the major paper of my current post doc after working for 3 and a half years on this. This was a major collaborative effort involving people across two labs so the paper has 9 authors, currently myself as first author and two equally contributing senior authors. I have spearheaded the project since funding acquisition (I've got a Marie Curie grant for this research) and it will really be the major paper with which I would ask for new fundings and try to potentially start up my research group.

The paper is finally ready for submission and I was asked yesterday by one of the senior authors if the current second author should be upgraded to co-first (I would still be first name and corresponding author together with the two seniors). If one looks at mere contribution (i.e. time spent working on the various experiments and data analyses), I've done way more work than any other person (it has always been my project so others helped but I worked 90% of my time only on this), and all of the project coordination, but the second author has contributed very important analyses and is helping substantially in manuscript writing. He has always had a super nice collaborative attitude and we worked closely for several months on the main experiment (main because it gave the coolest results, not because it involved 90% of the whole project, although it was still 4 months of solid work just to collect these data), but I do feel it would have been different (more work load on him also for this main experiment and more requests to work together also on different components of the study) if we had decided this at the beginning and not now upon submission.

Anyways my question is, does it make any difference for my future career or how this will look like from the perspective of an employer or for the community of researchers working on the same topic, whether we are co-first or not? Because if it does not change anything to me then I do not see any issue, but if it somehow would give the idea that I was not fully independent on this (in terms of developing the ideas, coordinating etc), then I would be a bit more reluctant as I am trying to establish some "leadership" recognition in the field with this work. What different thoughts the two scenarios would prompt on someone looking at the publication list on my CV for example?

Thank you all for your answers!

Answer 1

None.

There will be no difference in your CV. There is no space for such level of detail in the CV. If you spend precious space of your CV to describe how much formal contribution every author has given for each paper, you soon end up with pages of useless content.

Regarding "it somehow would give the idea that I was not fully independent on this (in terms of developing the ideas, coordinating etc)" you just state explicitly what each of the author contributed, I have seen such a disclaimer in many recent papers.

This paper has a lot of value for you (3+ years of work!), but an external reader would just look at the order of authors and think "the first author is the one that carried out the majority of the work". However, please clarify with the unnamed person that asked you to promote the co-author to co-first author that things would have been different for you "if we had decided this at the beginning and not now upon submission."

My final suggestion is that you are a postdoc, you are independent, you can politely refuse stating "he/she fully contributed as planned at the beginning of the work, he/she will be a co-author as planned at the beginning of the work".