Graduate students are a valuable commodity.
When I naively walked into my first rotation as a graduate student in a real lab, I believed that I was simply a nuisance, an obligation of higher scientists to perpetuate the cycle of science careers with fresh minds. As such, I was overwhelmed and honored when each of the three labs I eventually rotated in offered for me to pursue my thesis with them. Unfortunately for me, I was in an interdisciplinary program which promoted co-mentorship and had almost no ability to say ‘No’ to anyone. Thus, I entered into a ridiculous three-way mentorship thesis trying to collaborate between three labs. Don’t ever do that.
In fact, I think the entire concept of collaborative projects and mentorships for graduates students is a recipe for disaster. Any experienced Principal Investigator (PI) will tell you that collaborating effectively is one of the most difficult things to do in science. These programs expect novice scientists that are trying to learn the ropes of doing real research and that are, to be honest – still maturing adults, to navigate one of the most challenging scenarios in their career from day one. I think that that is just plain mean. The only successful collaborative thesis projects I’ve seen have been either collaborative only in name, or orchestrated by a graduate student with years of prior experience in the either science or collaboration.
The fact is that Graduate students are at a minimum cheap labor, as you may already know, but also an important line on any investigators CV. The number of students a PI has successfully mentored into a career in science has a significant impact on his ability to get grant funding, the life blood of academic research. It is also critical to the lab as a whole, because without a good track record in mentoring by the PI, students and post-docs in the lab will be at a disadvantage when applying for their own fellowship funding to support their salaries and research.
Being invited to do your thesis work in a lab is a great sign. It means that you have probably shown potential and a strong work ethic. But do not understand the invite to be a gift of generosity, whether you feel you deserve it or not. It is an exchange. You will receive a project, some mentoring (hopefully), and funding with which to carry it out (hopefully). The mentoring PI will receive ‘cheap as dirt’ labor for his most risky projects and a critical bonus to his CV and reputation. Whether this is a fair exchange or not is what you need to figure out before committing to a lab for the next 3-4 years.