Witnesses, not just stones

Witnesses Are Not Just Stones

Author: Mao Ning Science Popularization

The story of "Bird's Beak" takes place in the Galapagos Islands, officially known as the Galapagos Islands. It is a volcanic archipelago in the Pacific Ocean, located near the equator and belonging to Ecuador. These small islands are not very eye-catching on the map. The earliest record was in 1535, when the bishop of Panama accidentally drifted here when he went to Peru. However, the wildlife on this island is eye-catching: giant tortoises, iguanas, blue-footed boobies, rich marine life... Ground finches are one of the most common animals, but if you observe carefully, you will find that these ordinary-looking birds also have magical features. Their beaks are of different shapes and have their own duties. Some live on cacti, eat seeds, drink nectar, and build nests on cacti to reproduce; some can tear the skin of plants and eat young branches; some feed on parasites on iguanas; some are not so "glorious" and will peck boobies to suck blood. Well, if we ignore the factors that we don't like, the ecology of these small islands is simply Browning's poem: "God lives in heaven, and everything is perfect."

However, this island welcomed an uninvited guest in the 19th century, which completely changed our understanding of the island. Charles Darwin arrived at the archipelago during his trip with the Beagle in 1835 and collected a large number of specimens. He noticed that the beaks of the finches were layered. In his research notes, Darwin believed that these finches might be distributed to various islands. An idea was about to emerge: these finches had a common ancestor, and later evolved into many different species. This idea later became a masterpiece "The Origin of Species". This idea changed other people nearly 150 years later. Jonathan Wino followed a group of scientists: Peter Grant and Rosemary Grant and others to participate in the study of finches, and wrote a Pulitzer Prize-winning work "Bird Beaks" in 1994.

The Grants are legendary scientists who have spent most of their lives dealing with one species, the ground finches of the Galapagos Islands. They first visited the islands in 1973, accompanied by their graduate students and their two daughters. For nearly two decades, their research has focused on the ground finches. Their daughter spent her childhood on the volcanic island, and they were accompanied by a succession of graduate students and research assistants. They experienced droughts and floods, and observed changes in birds that were previously unimaginable.

All this needs to start with Darwin. Movies and TV shows like to write everything into a feature film: Darwin came to the island to see the finches, and shouted "discovery" like Archimedes! He went back and wrote a book about it. However, the actual situation is far more complicated than this. After Darwin returned to England, he did not publish "The Origin of Species" until 1859. Among the large number of organisms he studied throughout his life, it is difficult to say how much direct relationship there is between observing finches and the theory of evolution. However, the theory of evolution has brought a sense of urgency, and scholars who support this theory need further empirical evidence, more data, and more details. The ground finches are ideal objects of observation. On the small island, there are many kinds of ground finches with different habits. Their various forms, especially the form of the beaks, are they really the result of natural selection as predicted by the theory of evolution? Since the 20th century, many biologists have come to study. However, no one has stayed as long as the Grants.

Field work is hard. For example, the Dafen Major Island studied by Grant and other scientists is an uninhabited island. From a distance, it looks like a huge rock exposed above the sea. The finches on the island don't even fear humans. In those years, they struggled to get on this small island, not only to observe the finches, but also to find ways to survive in the wild. They divided the land into small plots, collected the food of all the finches on a piece of land, and estimated the total amount of food on the island. They put leg rings (rings) on all the finches as much as possible, recorded their kinship of each generation, and then used calipers to measure their body structure, especially the length, width, and depth of the beak. They even used something like a hand dynamometer to calculate those hard fruits and measure the energy required for birds to peck open the fruits and eat the seeds. These finches may be the wild creatures with the most detailed genealogy. After a few years, scientists can even tell their breeding status by looking at their leg rings.

1977 was a year with little rain, and the survival of the finches on the island was greatly threatened. This was just the beginning of a major drought. After a period of time, many finches starved to death, and even the thorns that the finches were reluctant to eat in the past were bitten open. At this time, the differences in bird beaks began to show advantages and disadvantages. Those finches with small bodies and small beaks found it difficult to obtain enough food. In normal times, these finches have similar difficulty in obtaining food, but once food is scarce, the easily accessible food is eaten first. The remaining fruits are too hard and consume a lot of energy to eat. For small birds, it is even impossible to peck them open. After the drought ended, the average size of the finches' beaks increased, and the mortality rate of those finches with too small beaks was much higher. Based on the data, Grant found that the difference between survival and death may be only 0.5 mm, and a smaller beak means being eliminated.

However, the power of nature is so fickle. In 1982, the El Niño phenomenon occurred, and huge amounts of rainfall came. The ground finches reproduced frantically. Scientists had just put leg rings on a nest of chicks, and a few months later they went to the island again to find that these first-year birds had begun to hatch eggs. This carnival did not necessarily bring comedy. The ground finches ate too much food, exceeding the rate of island plant production. Soon, floods brought another famine. This time, the power of natural selection "favored" the small ground finches. The number of small seeds exceeded that of large seeds, but this time, large birds with large beaks found it difficult to handle these small seeds. The breeding boom brought by the rainfall eventually killed the larger birds first.

These data reveal to people the details of evolution that have never been confirmed before: speed. We are often educated to believe that the birth of new species requires tens of thousands of years. Leaving aside this ambiguous statement, some scholars believe that the speed of physical changes caused by evolution is measured in millions of years through fossil evidence. However, the research of Grant and others revealed that in just a dozen years, the body size of the ground finches has undergone a tug-of-war, and some tiny differences in beaks can change life and death, and can determine whose genes will be passed down. For the masterpiece of evolution, the study of bird beaks has filled an important color block. Under the eyes of Grant and others, natural selection is taking effect. About eight million years ago, volcanic activity caused the archipelago to float out of the sea. Then the ancestors of cacti, iguanas, and ground finches came here by accident. Afterwards, this force witnessed by humans caused these ground finches to evolve into a variety of types. The conclusion of "Bird Beak" reads: "Darwin's finches will still strictly abide by the contract signed with Darwin's archipelago, and piles of stones will still be witnesses." However, there are more than just stones as witnesses. Over the past 20 years, a group of scientists have used their rigorous and detailed data to bear witness to the power of evolution and to the new proof of a most ingenious and beautiful theory. Humans are their own witnesses.

This article is produced by Science Popularization China-Starry Sky Project (Creation and Cultivation). Please indicate the source when reprinting.