A while ago, I read an argument that understanding economics is more important than understanding evolution. The author's point is that evolutionary theory does not provide the layman with particularly useful information, whereas economic theory has many applications, particularly in public policy. Therefore, as concerned citizens interested in promoting good public policy, we should give priority to learning about and discussing economic theory.
As much as it hurts my ego as an evolution researcher, the argument has a point. Evolutionary theories can seem pretty far removed from the general concerns of humanity (but see below). However, I'm not convinced that economics should take the top spot either, so I want to open up this issue for discussion. Before commenting on the value of different fields, I have the following general thoughts:
1) It's possible that we should not focus on scientific knowledge in itself. Perhaps the most important issue should be for people to know how to find and interpret scientific knowledge. If that's the case, then what matters is developing the skills of reading, math, and critical thinking.
2) It's possible that all sciences are connected such that it would make no sense to give precedence to one or another. Maybe the study of any field of science facilitates the study of every other field of science, either by providing background knowledge or by honing reading, math, and critical thinking skills. If that is the case, then perhaps a broad scientific education is best, supplemented by each person focusing on whatever interests them at the moment.
3) Aside from any qualites inherent to evolutionary theory, I think that evolution is worth emphasizing because it is the front-line of an assault on science. The topic obviously catches people's attention, and there is such a strong case for evolution that it provides a good opportunity to teach about science.* For another opinion on this issue, along with some discussion of general scientific literacy, see There's More to Science Than Evolution.
With that being said, here are some contestants. Nominate your own below:
Economics: Ideally, it can help you decide who to vote for, and how to run your business or financial investments. The thing I worry about is whether macroeconomic theories are really solid, and how applicable the theories are to one's own actions. At the least, it provides some understanding of the major economic institutions in our society.
Evolution: It provides some framework to all studies of biology (particularly, how model organisms are related to humans and other organisms of interest). It also provides practical understanding of phenomena like the spread of antibiotic-resistant pathogens.
Ecology: Invasive species, response to climate change, and all that.
Climatology: Well, there's the whole climate change issue, and I see no reason that it will ever go away.
Human physiology: This is my leading candidate for the most important field of scientific knowledge. This will inform all sorts of personal decisions, ranging from diet and exercise to decisions about medical interventions.
Electricity and Magnetism: It's everywhere in both nature and our technologies, but how much does the layman need to understand it?
Mechanics: F = MA. This may help people to build simple machines, as needed, and understand the machines that surround us.
Computer science: Programming is a useful skill, and computers are useful tools that can aid in thought about other topics. I'd almost classify this as a branch of math, rather than a proper science.
Chemistry: It's nice to be able to read the ingredients list. This may improve our understanding of water quality issues, and generally what it means to be "drenched in chemicals". Of course, it is also a pre-requisite for understanding biochemistry, including pharmacology.
Psychology: Can knowledge of psychology holp you to avoid common cognitive errors? Can it help you to raise you kids?
Sociology:This has all the strengths and weaknesses of Economics, though I suspect that the theories are even less well established.
That's all I can come up with off the top of my head. Human physiology seems to be the best to me, perhaps with psychology as a supplement. Any more thoughts?
*This is why I discussed evolution in my entry for the writing contest (vote once a day!)
What Is The Most Important Field Of Science For The Public?