The Galapagos Islands are the natural habitat of thousands of species and unique landscapes. There isn’t another place like it on the face of the Earth.
If you’re a lover of books (or a bibliophile) like me, you’ll appreciate Charles Darwin, the biologist famous for his Theory of Evolution that was formulated while visiting the Galapagos Islands. Arguably the most influential man of science in history, Darwin accumulated a vast personal library throughout his working life. Until now, however, 85% of its contents were unknown or unpublished. But this year, coinciding with Darwin’s 215th birthday (he was born on February 12, 1809), a scholarly project called Darwin Online has released a 300-page, online catalogue detailing Darwin’s complete personal library, with 7,400 titles across 13,000 volumes and items that include books, journals and pamphlets.
But a refreshed look back to the past isn’t the only news to come out of the Galapagos lately. Recently, a global team of biologists compiled nearly two decades of field data—representing the study of more than 3,400 Darwin’s finches in the Galapagos Islands—to identify the relationship between beak traits and the longevity of individual finches from four different species.
And, Darwin’s finches aren’t done teaching us lessons yet: they are once again providing insights into the Theory of Evolution. Two recent studies investigating their dealings with the avian, parasitic vampire fly (Philornis downsi) show us which finch species are the most successful hosts for the flies and how the birds cope with being infected. This knowledge will help researchers maintain and protect Galapagos finch populations while also providing strategies for dealing with other parasitic species around the world.
The history of the Galapagos Islands dates back millions of years with the volcanic formation of the archipelago. It was here that Charles Darwin conceived his Theory of Evolution.
“Fitness mountains” and finch longevity
Evolutionary biologists have long suspected that the diversification of a single species into multiple descendent species—or adaptive radiation—is the result of each species adjusting to a different environment. Yet formal tests of this hypothesis have been elusive, owing to the difficulty of firmly establishing the relationship between species traits and evolutionary “fitness” for a group of related species that recently diverged from a common ancestor.
Now, however, an international team of biologists led by researchers from Canada’s McGill University have compiled nearly 20 years of field data from four species of Darwin’s finches—which all evolved from a single common ancestor less than 1 million years ago—to identify the relationship between beak traits and longevity.
The scientists discovered that finches with the beak traits typical of each species lived the longest, whereas those that deviated from the standard traits had lower survival. In other words, the traits of each species correspond to fitness peaks that can be likened to mountains on a topographic map separated from other mountains by valleys of lower fitness.
Adaptive radiation is a rapid increase in the number of species with a common ancestor, characterized by great ecological and morphological diversity. The driving force behind it is the adaptation of organisms to new ecological contexts.
Biological species are diverse in their functions and shapes mainly because individual traits, such as beaks, are selected by the environments in which the species are found. As a result, the diversity of life is a product of the radiation of species to specialize in different habitats; in the case of Darwin’s finches, those environments are different food types.
Surprisingly, state the researchers in their article published in the science journal Evolution in December 2023, they also found that the different species of finches studied have not reached the top of their “fitness mountains,” suggesting that each species is not perfectly adapted to their food type—yet. Whether such “perfection” will ultimately evolve remains to be seen.
Fly invasions and fighting back
Back in the 1960s, the avian vampire fly Philornis downsi was accidentally introduced to one island in the Galapagos. Its blood sucking larvae are now spread across the islands, killing the offspring of land birds. The fly larvae feed on the blood and tissues of nestlings, including feeding inside the birds’ nostrils.
There are 17 species of Darwin’s finches found in the Galapagos Islands. They are not true finches; they belong to the tanager family. It is thought that their ancestor and closest known relative is the grassquit, found on mainland South America. Once the original grassquits arrived in the Galapagos, they diversified and adapted to the different environments found on the islands, eventually becoming different species. ©Agami Photo Agency/Shutterstock.com
Now, two new studies have explored how the various species of finches across the islands have been dealing with the fly, potentially providing further insight into the evolutionary pathways of introduced parasites.
In one study, recently published in the journal Scientific Reports and led by researchers from Australia’s Flinders University BirdLab, investigators looked at which species of finch proved to be the most successful hosts for the flies. They found that the fly’s larvae were most abundant and had the best survival rates inside the nests of the critically endangered medium tree finch, which lives only on Floreana Island, but it had less success in the nests of hybrid tree finches.
What’s interesting is that these findings are telling us a story from both sides; on one hand, it demonstrates that natural selection would favor those flies that target the threatened species, but it also shows us how the finches are fighting back. Since the arrival of the avian vampire fly, medium tree finches have started breeding with small tree finches to form a hybrid population. Nests belonging to these hybrid finches played host to fewer flies and had the lowest parasite survival rate, suggesting that hybridization between the small and medium tree finches may be their defense strategy against this invasive parasite.
The medium tree finch is endemic to Floreana Island and is only found in a small range of forested habitats in the highlands, such as evergreen forests, tropical deciduous forests and humid scrubs. A small, fast bird, it used to be found across Floreana, but in recent years the island has suffered extensive habitat destruction due to human activity and degradation by free-ranging livestock and invasive species, such as cats, feral pigs and rats.
In a second project, scientists looked at how the birds cope with being infected by the parasites. They measured each nestling’s “behavioral type” by recording how much it struggled during human handling and then compared this with how much damage the baby birds sustained from the flies.
The results, published in the Biological Journal of the Linnean Society, showed that nestlings that struggled more during handling also tended to have more deformed nostrils due to vampire fly parasitism. While it’s not known yet why this is the case, one possibility is that more vigorous nestlings are unwittingly attracting parasitic larvae to them by moving around inside the nest. Over time, more docile nestlings may survive to adulthood at greater rates, which could potentially change the behavioral traits of Darwin’s finches at a population level.
Understanding how the finches are evolving to deal with the parasite will not only help us protect Darwin’s finches from extinction, but it may also provide strategies for dealing with other parasitic species around the world in the future.
Charles Darwin is known as the architect of the Theory of Evolution by natural selection. With the publication of “On the Origin of Species” in 1859, he advanced a view of the development of life on Earth that profoundly shaped nearly all the biological and much of the philosophical thought that followed. Although prior authors had proposed that species were capable of change over time, Darwin was the first to argue that a wide variety of biological features could be explained if all organisms were descended from a single common ancestor and modified by a process of adaptation to environmental conditions that Darwin christened “natural selection.” ©Everett Collection/Shutterstock.com
Philosophical tomes and forgotten folios
This year, coinciding with Darwin’s 215th birthday, the Darwin Online project went live, providing an unprecedented, detailed view of the naturalist, geologist and biologist’s entire library. While previous lists had only 15% of his whole collection, this project virtually reassembled it all, with 9,300 links to copies of the works freely available online.
After Darwin’s death in 1882, much of his library was catalogued and preserved, but many other items were dispersed or lost, and the details of most of the contents had never been published. For many years, scholars have referred to Darwin’s library as containing 1,480 books, based on those that survive in the two main collections, England’s University of Cambridge and Down House, the home of Charles Darwin in Downe, England.
Over 18 years, the Darwin Online project has identified thousands of Darwin’s obscure references in his own catalogues and lists of items such as journals and pamphlets that were originally in his library. Each reference required its own detective story to discover the publications that Darwin had hurriedly recorded. In addition, missing details such as author, date or the source of clippings in thousands of records from older catalogues have been identified for the first time.
Charles Darwin lived with his wife, children and servants in Down House, a Georgian manor 15 miles south of London in the Kent countryside, for 40 years; from 1842 until his death in 1882. It’s where one of his two main library collections also resided.
A major source of information that helped to reveal the original contents is the 426-page, handwritten Catalogue of the Library of Charles Darwin, compiled from 1875. Painstaking comparison of its abbreviated entries revealed 440 unknown titles that were originally in the library. An inventory of his home made after his death recorded 2,065 bound books and an unknown number of unbound volumes and pamphlets. In the drawing room, 133 titles and 289 volumes of mostly unscientific literature were recorded.
Other sources of information that helped to build Darwin’s complete library were lists of pamphlets, Darwin’s reading notebooks, his spouse Emma’s diaries, the catalogue of books given to the Cambridge Botany School in 1908 and the 30 volumes of the Darwin Correspondence Project. Items that still exist but were never included in the lists of Darwin’s library include his unbound materials at Cambridge University Library, books now in other institutional collections, private collections and books sold at auctions over the past 130 years. Combining these and many other sources of evidence allowed the naturalist’s library to be reconstructed.
For example, Darwin’s copy of an 1826 article by the ornithologist John James Audubon, Account of the Habits of the Turkey Buzzard (Vultura aura), Particularly with the View of Exploding the Opinion Generally Entertained of its Extraordinary Power of Smelling, was sold in 1975. Darwin had investigated this point during the voyage of the HMS Beagle and recorded reading a critic of Audubon in a Galapagos notebook. In 2019, a copy of Elizabeth Gaskell’s 1880 novel Wives and Daughters appeared at auction. A note in it records: “This book was a great favorite of Charles Darwin’s and the last book to be read aloud to him.”
During the voyage of the HMS “Beagle” in 1831, Charles Darwin read, among other things, John Milton’s “Paradise Lost,” Samuel Richardson’s novels about the fictional, virtuous hero Sir Charles Grandison and Charles Lyell’s “Principles of Geology.”
Many of the works in Darwin’s library are on scientific subjects, especially biology and geology. Yet, the library also included works on animal breeding and behavior, farming, geographical distribution, philosophy, psychology, religion and other topics that interested Darwin, such as art, history, language and travel. Most of the works are in English, but almost half are in other languages, especially French, German and Italian, as well as Danish, Dutch, Latin, Spanish and Swedish.
Some of the hundreds of books not previously known to be in Darwin’s library include Sun Pictures, an 1872 coffee-table book showcasing photographs of artworks. Another was a copy of the popular science book on gorillas that was all the rage just after On the Origin of Species was published: Paul Du Chaillu’s Explorations and Adventures in Equatorial Africa. Thousands of shorter items were also found in Darwin’s library, such as an issue of a German scientific periodical sent to him in 1877 that contained the first published photographs of bacteria and another article amusingly titled The Hateful or Colorado Grasshopper.
Fact-finding and following an example
Darwin’s finches are a classic case of evolution and will forever be tightly linked to Charles Darwin’s Galapagos voyage and his groundbreaking theory. Still today, these little birds are teaching us important lessons on longevity, natural selection and how species evolve when a parasite is introduced into an island system.
Like Darwin, I’m a confirmed bibliophile. We can all learn a lot if we emerge once and a while from our own echo chambers.
Through his complete library, Charles Darwin, too, is instructing us in knowledge-gathering. His choice of reading material shows us that he was not an isolated figure working alone but an expert building on and listening to a spectrum of sophisticated science and scientists and the wide-ranging studies of thousands of people around the world.
Now, in a time when it can seem like every one of us lives in our own echo chamber—an environment where we only encounter information or opinions that reflect and reinforce our own—it’s a good example to follow.
Here’s to finding your true places and natural habitats,
Candy
