Why biology is hard – the physics of cats

The little thought experiment that forms the basis of this post is taken from Professor Charles Marshall via Musings regular Corwin Sullivan and aptly demonstrates why an awful lot of biology is really quite hard to study when compared to the other sciences (most notably physics and chemistry).

Let us consider a standard billiards table (though bar billiards should be recognised as one of the greatest games ever, it is perhaps not the best for this example, and a cannon billiards table might be even better, but so obscure I doubt even many British readers have come across one, anyway…) and on this table lets put three balls in a row evenly spaced across the width of the table. Now, hit each ball in turn gently, aiming straight down the table as evenly as possible (that is, try to make each shot have the same power and no spin). What will happen to the balls?

Assuming you are even vaguely competent each ball should travel down the table hit the opposite cushion and bounce back a little. They should each take the same path and stop at about the same point. If you are feeling especially scientific you could make a machine to do the hitting, and use a set square to set up the shots to make them as straight as possible.

Now let’s repeat the experiment but replace the three balls with three cats. Anyone want to try and predict what will happen when each is poked with a snooker cue? Can we even get three cats that are identical to start the experiment? Even clones would be different in some small ways and would probably react differently. Hmmmm, bit tricky this.

Yes, it’s silly, and obviously grossly exaggerated, but hopefully it does make a point (though it might upset a few physicists and chemists). Dealing with living organisms is really complex because a reductionist approach is often not appropriate (you can split the cats down to their constituent atoms or molecules which *would* react in a predictable way, but it would not tell you much about the cats, though it might be fun) and the sheer variety of individuals within a population, let a lone a species or family is absolutely enormous. You can probably identify significant differences between yourself and your parents and siblings (both physical and behavioural), let alone your great grandparents or second cousins. Thus when talking about them we have to be general “cats typically react in manner X to stimulus Y”, “cats typically have  long tail” and dealing with low numbers of data points (as is normal in palaeontology) risks mistaking an outlier or part of typical variation as normal or common.

Take a look at 50 atoms of iron and you won’t see much variation (and what you will see is predictable, like the loss of an electron) do the same with 50 cats and you probably won’t scratch the surface of the variation (though you yourself will probably be scratched extensively). Conclusion: biology is hard.

It should of course be noted that in fact all science is hard in general.

7 Responses to “Why biology is hard – the physics of cats”


  1. 1 tanystropheus 11/02/2009 at 10:45 am

    Interesting post, David!

    It’s a sad fact that even today biologists are the subject of much condescention at the hands of physicists and chemists. I daresay that I’ll make use of this analogy the next time someone belittles my field!

    I quite enjoy your blog by the way!

    -Mark

  2. 2 mythusmage 11/02/2009 at 11:23 am

    One pool table, one cue, one ball, one cat. Have fun. 🙂

  3. 3 David Hone 11/02/2009 at 7:20 pm

    It’s a catch 22 Mark, if you point this out to them, their reply will be that we can;t ever be sure of anyhting, since not even clones are identical, how to we test ideas about e.g. species. We have to deal with probables (and in palaeo, possibles) and with statistical likelyhood, it certainly makes our task far harder and to a degree theirs easier.

  4. 4 Nathan Myers 12/02/2009 at 11:31 am

    So, physics is the Trivial Science; they should have made a lot more progress by now. How are they coming on understanding that high-temperature superconduction and quantum gravitation stuff, anyway? Excuses, excuses are all I hear.

  5. 5 David Hone 12/02/2009 at 9:40 pm

    Joking aside, we might actually be doing stuff of that technical level in biology were it not for the fact that we still can;t sort out the basic taxonomy of clades like cats, are finding tens of thouands of new species annually, have entire genomes to play with (which makes even organic chemistry look ordered) let alone the proteins, and stuff as variable and unquatifiable as behaviour to contend with. It does make life harder when every time you do the test it returns a different, even potentially opposite result. Ok, so that happens to the quantum physicists too, but that stuff is just nuts, rather than complex.


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