Universal laws and historical contingency in evolutionary biology

Why would someone interested in science prefer physics to biology? My first guess is that physics seems cleaner: a small set of mathematical rules, rather than the variety and complexity of living things. The opening gives a more precise explanation. These philosophers mistrust uncertainty and expect science to identify what holds everywhere and always.

Under that picture, science studies repeatable phenomena governed by universal laws. Something that happened only because of a particular set of circumstances looks more like history. That doesn't mean we should simply declare biology false or unscientific. We're being introduced to a standard for what science ought to explain, and to the discomfort that standard creates.

The elephant-and-mouse example makes the preference concrete. These philosophers are interested in the rule governing how the animals fall, despite their different sizes. They are less interested in the history that produced those different sizes. Same animals, different questions: what general law governs them, or how did these particular outcomes come about?

Paragraph 2 moves from the philosophers to biologists who have adopted the same ideal. These biologists seek their own versions of the law of gravity. A universal struggle for existence and a constant, clocklike rate of DNA evolution are offered as examples of that effort. We don't have to decide whether those claims are scientifically correct. Here, they show what a law-seeking approach looks like.

Then comes the disagreement. Other biologists question whether biological history must unfold exactly as universal laws dictate. They leave room for historical contingency: what happens can depend on the particular course events take. That's more precise than saying biology has no laws or everything is random. The question is whether universal laws fully account for the outcomes or whether the history also matters.

The next paragraph is dense, so simplify its job before getting lost in the terminology. We're comparing those two approaches through two statements that sound equally sweeping: all planets move in ellipses, and all swans are white.

The planetary statement is presented as a consequence of laws governing motion in a gravitational field. It covers not just the planets we happen to have, but planets that could exist. On this account, the law requires the result. It isn't merely a report that every planet in a particular collection happened to behave that way.

Now suppose all the swans in the collection are white. Would that establish the same kind of necessity? My instinct is to ask whether a different environment or a different history could have produced a swan of another color. Seeing the same trait in every member of a collection doesn't, by itself, answer that question.

The determinists would say that natural-selection laws make the result necessary. The account connects those laws to reproductive success and the eventual appearance of favored traits. I still want the missing explanation of why those principles would require this particular color. But that reaction shouldn't obscure the view being described: the result isn't just how things happened to turn out.

Nondeterminists deny that necessity. Swans can be a finite historical collection whose members happen to share a trait without making another outcome impossible. Both statements begin with all, but that wording alone doesn't establish that both describe universal laws.

My initial expectation was a discussion of why philosophers prefer physics. By the end, the central issue is the disagreement within evolutionary biology. The opening sets it up; the later paragraphs develop it. A good main-point prediction must follow that shift: biologists disagree about how far universal laws explain the phenomena they study.