How to determine the status of human embryos

Wednesday, 2 April, 2008

This bioethics twist on the classical ‘fat-man trolley problem‘ of moral philosophy can be used to determine whether a person considers embryos to be full human beings or not, and exactly how much of a human being an embryo is. So, here it is:

A train is hurtling down a track, and on this track is a single railway worker, unaware of the train. You are on a bridge under which the train will pass, and you can stop it by dropping a heavy weight in front of it. For reasons unknown, there is a refrigerator (from the local IVF clinic) on the bridge next to you, which you know contains a thousand human embryos – your only way to stop the train is to push the refrigerator off the bridge and onto the track, killing all thousand of the human embryos to save the life of the railway worker. Should you push the refrigerator off the bridge?

If this seems confusing, there is another very similar example that may make more sense because of its more realistic premise (though, technically, it is a version of the original trolley problem, not the fat man version):

Imagine that an IVF lab is on fire. A fireman realises that the roof is about to collapse and that he has very little time left, only enough to rescue either a tray of 1000 frozen embryos, or the lab technician, who is already unconscious because of the smoke. What should the fireman do?

To determine the moral status of a human embryo, all you must do is vary the number of embryos until it becomes immoral for them to be destroyed in the process of saving a life. Let that number of embryos be [E], then the perceived status of the embryo is PS, given by:

PS= 1/[E]


PS = perceived status of the embryo (1 is a full person, 0 is not a person at all)

E = number of embryos required to make their destruction in saving a single adult’s life morally unacceptable

The result you get from this thought experiment essentially can determine whether you are in favour of using human embryos in medical research or not (like embryonic stem cell research). The higher your PS score, the more likely you are to oppose embryo-destructive treatments and procedures. The lower your score, the more likely you are to be in favour of using human embryos to discover treatments for human diseases.

The fun part is when people hold the wonderfully contradictory position of having a low PS score but are hostile to embryo research (I’m sure the reverse is possible, but I don’t know anyone who holds it). Sparks fly with accusations of hypothetical hypocrisy!



  1. Okay, but does the train have passengers? An engineer(s)?

    One can throw all kinds of variables into this scenario to justify any moral claim.

    But I’m going to assume it’s a run-away train so I would have no problem throwing the embryos ‘under the bus’, or train in this instance to save the worker. Plus the worker probably has a family.

    Plus I’ll admit a selfish interest in stem cell research because of my chronic illnesses.

    No moral problem here.

  2. Yes, because it is a thought experiment, we can assume that pushing the refrigerator off the bridge has no chance of killing anyone on the train.

    My PS score is almost zero, because I can’t see any reason to favour a bunch of human cells over fully functional human being.

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