by PhilipJ on 3 January 2008
Biological processes of course are consequences of physics and chemistry, which is why we require our biology students to study the physical sciences. But organisms are also historical entities, and that’s where the complexities arise. The facts of physics and chemistry are constant across time and space. Any one carbon atom is the same as any other, and today’s carbon atoms are the same as those of a billion years ago. But each organism is different. That’s not just a statement that fruit flies are different from house flies. Rather, each fruit fly is different from every other fruit fly alive today, and from every other fruit fly that ever lived, and it’s the differences that make biology both thrilling and hard.
No disagreements from me here. The laws which govern physics and chemistry are contant across the universe (though there is some debate as to their constancy in time). Without the strict adherence to the laws we observe, physics and chemistry would be near impossible to understand. It is lucky for biology that this is how the world works, because, as Rosie notes, biology depends on it!
Skipping ahead, here’s where I get confused:
Even genetically identical cells are not functionally identical. When a cell divides its molecules are randomly distributed between the two daughters; because ‘randomly’ does not mean ‘evenly’, these daughters will have inherited different sets of the proteins and RNAs that carry out their functions. And even if the two cells had identical contents, these contents would still have different interactions – repressors bump into cofactors at different times, DNA polymerase slips or doesn’t slip at different points in its progress along a chromosome. Understanding the how and why of biological phenomena thus requires us to consider historical and ecological factors that are many orders of magnitude more complex than those of physical systems.
When trying to understand biological systems (nay, any kind of system, be it a crystal or a batch of cells), much ultimately depends on the type of measurement. Every measurement does not need to take into account the histories and ecological factors that make up every individual cell – it is impossible to know them to the required resolution that such data would be useful. When and where a DNA polymerase may stall on the chromosome in a particular cell of a mL culture containing billions upon billions of cells is effectively irrelevant for a huge number of interesting experiments I might want to do with those cells — say, the study of expression of a particular gene with a gene chip.
The critical word is probably ‘population’. Biologists rarely try to define it, but they use the term everywhere to refer to similar but not identical organisms or cells (or even molecules) that interact in some way. ‘Population thinking’, the realization that species are populations, not pure types, is said to have been key to Darwin’s insight that members of a species undergo natural selection. And population thinking is probably what makes biology so much more complex than the physical sciences.
Here’s where I think my ultimate displeasure with the post lies. That biology is more complex than physics (though what exactly is limited to the realm of physics is now very much in question) is a reasonable statement: the most common biological molecules are much too complicated to apply something like the Schroedinger Equation and expect to understand anything about them, but “complex” and “difficult” are not the same thing. That physics has traditionally been confined to the well-defined and “simple” systems like infinite lattices of identical carbon atoms, doesn’t make it “easier” to study than biology. I don’t even know what it could mean for one field of science to be “easier” than another, given that everyone studying a science is different, like, as Rosie mentions above, how each fruit fly is different from every other fruit fly. Some people find the mathematics required to understand physical systems extremely difficult, while others don’t have the required attention to detail to perform a successful experiment in a biology lab. To do any kind of science, however, it is the same: you require critical thinking and quantitative analysis of experiments to make any sense of your results. This is true from particle physics all the way up to ecology.
Rosie’s opening paragraph ends with the following:
[I]n reality biology is much more complex than the physical sciences, and understanding it requires more, not less, brain work.
I hope someone in the social sciences gets wind of this and belittles biologists. Sociology is obviously more complex than biology, so it cleary requires more brainpower to be a social scientist than a biologist, right? Rutherford’s famous statement that all science save physics is mere stamp collecting wasn’t a useful thing to say, and this isn’t much better.