Themes
Key
LitCharts assigns a color and icon to each theme in The Beak of the Finch, which you can use to track the themes throughout the work.
Natural Selection and Evolution as Ongoing Processes
Nature and Humanity
Evolution, the Modern Era, and Nature’s “Resistance Movement”
The Interconnectedness of Species and Ecosystems
Hybridization and Specialization
Summary
Analysis
Back in Princeton, the Grants are well into their sabbatical year. Their data has revealed that since the El Niño of 1982-83, the adaptive landscape on the islands has changed dramatically. There is far less Tribulus and cactus, but more soft, small seeds. So the ground finches who feast on those seeds are doing well, while the cactus finch population is suffering. There are only about 100 left—the lowest their numbers have been since the finch watch began in the 1960s. Yet the cactus finches themselves haven’t changed or adapted—they have no other “adaptive peak” to fly to.
This passage is significant because it illustrates how hyper-specialization can sometimes become a liability for a species. When the cactus finches’ food source dried out, there was no other “adaptive peak” or specialized niche for them to move toward. So their numbers began to crash. Sometimes, rather than ensuring a species evolves toward a new adaptive peak, specialization can box a species in.
Themes
The medium ground finches, too, have been affected—they are flexible in what they can eat, but only to a certain point. Fortis with deeper, wider beaks are dying—but those born after the flood with narrower beaks were doing better. They have been able to adapt, survive, and nearly replace themselves. After the flood, hybrids, too have been thriving, showing that in a place that changes as rapidly as Daphne Major, it can be advantageous to be on the slope of an adaptive peak rather than firmly at the top.
Being too close to the peak of an adaptive niche was a liability for the cactus finches, who had nowhere else to go and nothing else to eat when their food source dried up. But a species that might not be hyper-specialized or perfectly suited to one specific niche will, in times of trouble or chaos, have an easier time finding a way to survive because they are more adaptive and more variable.
Themes
When an adaptive landscape changes dramatically—when a new species wanders into very different territory, for instance—the genetic changes that will allow that species to suitably adapt over time are very large. Two evolutionists, Richard Lewontin and L.C. Birch, published a study in 1966 concerning the adaptive capabilities of fruit flies who migrated from warmer weather to cooler weather. The flies changed as they moved farther from home—and Lewontin and Birch hypothesized that because the original species once lived side by side with a similar species, the two different species passed genes back and forth. The mixture of genes, the two researchers suggested, allowed the flies to expand their landscape.
This passage illustrates an experiment in which two researchers discovered that hybridized genes were actually advantageous for a species that was trying to migrate and change. Being a jack-of-all-trades is often better than being a master of one when it comes to evolution. If a species has genes or traits that allow it to survive well in multiple scenarios, it stands to reason that it will do better than its hyper-specialized peers.
Themes
The Grants have taken this research one step further—they’ve begun to believe that while hybrid offspring might not normally be fit for a given environment, a “rare event” like a drought, plague, or flood can so transform the adaptive landscape that which traits are favored shift immensely and there is a slow fusion of populations. The pendulum swings constantly: sometimes hybrids are at a disadvantage, other times at an advantage. It’s hard for fusion to fully take place, though, before fission—environmental change—swings the other way. The Grants have witnessed these swings numerous times over the decades, and they’ve concluded that hybridization between species “provides favorable conditions for major and rapid evolution to occur.”
As the ecosystem shifts around any given species, they might be pressurized to become hyper-specialized and fill a specific adaptive niche. But what this passage suggests is that environmental havoc might also create a situation in which greater variability and adaptability—traits that are conferred, as seen in the fruit flies, through hybridization—are most useful. This push and pull moves species toward and away from evolution over and over again. Again, while the smaller components of the evolutionary process can often happen very quickly, a species’ full evolution is a careful process that must be sustained for a long time.
Themes
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Hybridization among birds was once thought to be very rare—but among the 9,600-odd species of bird alive today, interbreeding is far more common than it once seemed. New hybridization most commonly takes place between different varieties of plants, and it’s also been observed often among toads, insects, and fish—generally, within populations that stay in the same place. But in a case like the Galápagos finches, it’s becoming clear that every so often, a certain lineage needs “an infusion of fresh variation”.
A species that stays forever the same will have trouble adapting as its landscape and ecosystem change around it. And because change is the only constant—whether that change is fast and brief, like the changes caused by El Niño, or more slow-moving and ongoing—species that have “fresh variation” and a greater capacity for adaptability will do better than those that are concretely fixed and unable to interbreed.
Themes
“Reticulate evolution” is the name for a kind of evolution that appears more like a tangled thicket and less like the distinct branches of a tree. This kind of evolution doesn’t bind lineages together forever—so it’s been historically overlooked. But the Grants are taking care to call attention to how their finches engage in this kind of evolutionary behavior. This messiness creates the “bountiful diversity” that defines life on Earth. The forms of living things are constantly in flux—in spite of the invisible borders around them.
The term “reticulate evolution” seems to aptly describe the kinds of changes taking place among the Galápagos finches. Rather than constantly branching off onto new limbs and separating themselves from one another, the finches’ evolutionary patterns are entangled and circuitous. The finches change based on their environment—and while new speciation doesn’t always happen, the finches are able to find new ways to change and survive continuously based on the demands of their environment.
Themes
