I'm assuming you're using "global maximum" as a synonym for "pareto optimal," though I haven't heard it used in that sense before. There are plenty of papers arguing that one biological trait or another is pareto optimal. One such (very cool) paper, "Motile curved bacteria are Pareto-optimal," aggregates empirical data on bacterial shapes, simulates them, and uses the results of those simulations to show that the range of shapes represent tradeoffs for "efficient swimming, chemotaxis, and low cell construction cost."
It finds that most shapes are pretty efficient swimmers, but slightly elongated round shapes and curved rods are fastest, and long straight rods are notably slower. However, these long straight rod-shaped bacteria have the lowest chemotactic signal/noise ratio, because they can better resist being jostled around by random liquid motion. Finally, spherical shapes are probably easiest to construct, since you need special mechanical structures to hold rod and helical shapes. Finally, they show that all but two bacterial species they examined have body shapes that are on the pareto frontier.
If true, what would this "pareto optimality" principle mean generally?
Conservatively, it would indicate that we won't often find bad biological designs. If a design appears suboptimal, it suggests we need to look harder to identify the advantage it offers. Along this theme, we should be wary of side effects when we try to manipulate biological systems. These rules of thumb seem wise to me.
It's more of a stretch to go beyond caution about side effects and claim that we're likely to hit inescapable tradeoffs when we try to engineer living systems. Human goals diverge from maximizing reproductive fitness, we can set up artificial environments to encourage traits not adaptive in the wild, and we can apply interventions to biological systems that are extremely difficult, if not impossible, for evolution to construct.
Take the bacteria as an example. If this paper's conclusions are true, then elongated rods have the highest chemotactic SNR, but are difficult to construct. In the wild, that might matter a lot. But if we want to grow a f*ckload of elongated rod bacteria, we can build some huge bioreactors and do so. In general, we can deal with a pareto frontier by eliminating the bottleneck that locks us into the position of the frontier.
Likewise, the human body faces a tradeoff between being too vigilant for cancer (and provoking harmful autoimmune responses) and being too lax (and being prone to cancer). But we humans can engineer ever-more-sophisticated systems to detect and control cancer, using technologies that simply are not available to the body (perhaps in part for other pareto frontier reasons). We still face serious side effects when we administer chemo to a patient, but we can adjust not only the patient's position on the pareto frontier, but also the location of that frontier itself.
Do you have a source in mind for photosynthesis efficiency?
According to this source some algae have photosynthetic efficiency above 20%:... (read more)