by James Morris
Illustrations by Hannah King
Last week was the NBA trade deadline. Many teams had to decide between building for the future by acquiring young players and draft picks, or making a run for the playoffs this year by acquiring more experienced players in their prime. So what we see are trade-offs, which turn out to be all over the place, even in biology.
We are all faced with difficult decisions from time to time. Some are small, like which kind of toothpaste to buy, and some are large, like whether or not to accept a job in a new city.
With any type of decision comes something gained and something lost. A basketball player may try to make a 3-point shot (difficult, but worth 3 points), but in so doing, may give up the chance for an easy lay-up (easier, but only worth 2 points). Many of us are torn between work and home – time spent at the office means less time at home, and vice versa.
The word “decide” doesn’t mean choice or possibility or even opportunity. Instead, it comes from the Latin de meaning “off” and caedere meaning “cut,” the same root that’s in “scissors.” So, the emphasis is on what is cut off or lost, not what is gained. Perhaps this is one reason why making decisions is so difficult for some people.
At the heart of many decisions is what’s called a trade-off, or simply the idea that when you gain something in one area, you often sacrifice something in another. Simply put, you can’t have it all. Choices have to be made. And choosing one thing can mean losing another.
Charles Darwin recognized this dilemma when he made a list of the pros and cons of getting married. In one column, he wrote all of the benefits of getting married. In the other, he listed all of the benefits of not getting married. In so doing, he realized that he couldn’t have it both ways. After weighing his choices, he decided to get married, and was married for 43 years until his death in 1882.
An example from everyday life is a futon couch. It’s both a couch for sitting and a futon for sleeping. But it’s also kind of neither. That is, as anyone who has sat or slept on one knows, it is not very comfortable as a couch or as a bed. That’s because it is trying to be two things at once. And any improvement in one function decreases its function in the other. That’s a trade-off.
Trade-offs show up all over the place. In architecture, there is sometimes a trade-off between aesthetics and safety (or, more basically, form and function). In physics, the rate of a process and its efficiency are often at odds. In technology, an image can be sent more quickly if it is smaller, but then it loses quality. And in economics, trade-offs are expressed as opportunity costs. When two mutually exclusive options exist, the opportunity cost is the cost of the choice not made.
Trade-offs also exist in medicine. Think of commercials on television for prescription drugs. They begin with a short list of benefits, and then continue with a laundry list of side effects, many of which are life-threatening. And medical treatment plans often walk a thin line between extending life and quality of life.
The human body itself is full of trade-offs. Consider the bones in our body. They are strong so they resist breaking. But they are light, so they are not too cumbersome to carry around. Any improvement in one of these functions decreases it in the other. Increasing the strength of a bone, for example, will inevitably make it heavier, requiring more energy to produce and move. So bones represent a compromise. They are not perfectly strong (they break from time to time) and they are not overly cumbersome (we can move about). They are somewhere in between.
Or consider the human back. We get the benefits of walking upright (freeing our hands, a bigger brain), but the cost is neck and lower back pain.
Our cells can divide and move about. But that leaves us vulnerable to cancer.
It turns out that trade-offs are a theme in biology. Probably one of the most famous examples comes from how organisms devote resources to producing offspring. At one end of the spectrum are organisms like pine trees and fish that produce large numbers of offspring but put in little or no parental care. At the other extreme are organisms like us that produce few offspring but put in a tremendous amount time, energy, and resources into their care. In both cases, we see a trade-off between number of offspring and amount of energy invested in raising and caring for young.
Sexually selected traits also represent a trade-off. These are traits that increase an organism’s ability to attract a mate, like the bright colors, melodious songs, and courtship dances of many male birds. These traits attract females, but also take energy and may attract predators. They typically end up at somewhere in the middle between these two competing forces.
Why do trade-offs exist in nature? One reason is not so different from what we see in economics. With finite resources, time spent or energy put into one task takes away from other tasks. How to allocate limited resources is a common theme in both biology and economics.
In addition, most structures and organs don’t do just one thing. They have several competing functions and therefore several different simultaneous demands. Our bones don’t just hold us up – they are also the site of red blood cell production. Making bones stronger by increasing their thickness would reduce their ability to produce red blood cells.
Note too that functions change over time: Our lungs, used for breathing, evolved from the swimbladder of fish, used to adjust buoyancy in the water. Our jaws, used for chewing, evolved from arches used to support gills. Our ear bones, used to conduct sound, evolved from bones that were once part of the jaw. As a result, many structures are caught in the middle between functions they once performed and ones they currently perform.
As Charles Darwin wrote in On the Origin of Species, “The illustration of the swimbladder in fishes is a good one, because it shows us clearly the highly important fact that an organ originally constructed for one purpose, namely flotation, may be converted into one for a wholly different function, namely respiration.”
Or, as the evolutionary biology Stephen Jay Gould put it, “History matters.”
© James Morris and Science Whys, 2015.