Image: Ecologist Arthur Hasler (left) is best known for explaining the homing behavior of silver salmon. (University of Wisconsin-Madison Limnology Research Center)
Silver salmon (aka silver salmon) is a magical fish. Native to the Pacific Northwest, they hatch from freshwater and begin to migrate to the ocean. When the breeding season comes, they return to freshwater areas for production, 400 miles (644 km) apart.
Arthur Hasler, an ecologist and biologist at the University of Wisconsin, was curious about the behavior of silver salmon in finding the waters where they were born. In 1960, he used a fundamental scientific principle— the hypothesis — to find the answer.
What is a hypothesis? The hypothesis is a tentative, testable explanation of phenomena observed in nature. The scope of concern for hypotheses is small, which is different from theories that can cover a wide range of observable phenomena and draw conclusions from different evidences. And, if your hypothesis or theory is accurate, then the real result is the result you predicted.
Back to 1960's Hasler and Silver Salmon. One of Hasler's immediate ideas was that silver salmon rely on their eyes to locate their water systems. To test the idea, Hasler first found several fish that had returned to the birth stream, then covered some of the fish's eyes, some of them unchanged, and then threw the fish into another distant sea. If the conjecture of eye localization is correct, then the blindfolded fish will not return to the original waters.
Things went beyond expectations. Both the blindfolded and unbalamed fish returned to the original waters at the same rate. (There are other supporting experiments that prove that smell, rather than vision, is key to a species' homing behavior.) ）
While Hasler's blindfold hypothesis has been shown to be false, there are other, better examples. Today we look at three of the most famous experiments in history and the methods used to test hypotheses.
Pavlov and His Dog (1903-1935)
Hypothesis: If a dog is affected by a conditioned reflex (say, drooling), then dogs that often receive the same neutral stimulus (metronome or ringtone) before receiving food will associate this stimulation with eating behavior. Finally, when the dog encounters the above stimuli, it will drool unconsciously, even if it is not fed any food.
Experiment: The name of Nobel laureate Ivan Pavlov is also considered synonymous with mankind's best friend. In 1903, the Russian-born scientist began decades-long experiments involving various conditioned reflexes in dogs.
Put a plate of food in front of a hungry dog and it will drool. In this case, the stimulus given by the food automatically triggers the conditioned reflex of drooling, which is an innate, untrained response.
In contrast, a metronome or ringtone is a neutral stimulus. For dogs, noise doesn't make any sense and doesn't produce any instinctive reactions, but seeing food produces an instinctive reaction.
Therefore, whenever Pavlov and his experimental assistants fed the dog, they would play a metronome or bell, allowing the dog to mentally associate the metronome or ringtone with the meal. Due to repeated experiments, whenever a sound is heard, even if it is not fed, the dog will unconsciously drool.
According to biographer Daniel Philip Todes in his biography Ivan Pavlov: A Russian Life in Science, Pavlov's great innovation was his ability to quantify each dog's response by measuring the amount of saliva produced by it. When each dog encounters food-related stimuli, it secretes saliva at a rate.
Pavlov and his assistants also used conditioning to study the assumptions of other animal physiology. In a famous experiment, a dog was tested with its ability to distinguish time. When the metronome strikes at a rate of 60 times per minute, the dog gets food. But after a slow pace of 40 beats per minute, it didn't get any food. The results showed that Pavlov-trained animals could secrete saliva at a faster pace than a slower pace. Obviously, it can distinguish between these two rhythmic beats.
Conclusion: With the right conditioning, coupled with a lot of patience, you can get a hungry dog to respond to neutral stimuli and drool under prompts in a way that is both predictable and scientifically quantifiable.
Image: Pavlov proved that a hungry dog can produce a drooling response under neutral stimulus. HOWSTUFFWORKS
Newton's Prism (1665)
Hypothesis: If white light is a mixture of all colors in the visible spectrum, and they propagate at different wavelengths, then when a beam of white light passes through the glass prism, each color will be refracted at a different angle.
Experiment: Before Isaac Newton, color was a scientific mystery. In the summer of 1665, Newton experimented with glass prisms in a dark room in Cambridge, England.
He opened a round hole of a quarter inch (0.63 cm) in a shutter, allowing a beam of sunlight to enter the darkroom. When Newton held up a prism to the light, a rectangular multicolored light was projected onto the opposite wall.
It contains separation layers of red, orange, yellow, green, blue, indigo, and violet. From top to bottom, this layer of light is 13.5 inches (33.65 cm) high and only 2.6 inches (6.6 cm) in diameter.
Newton deduced that these colors were hidden in sunlight, but that when the prism bent (or "refracted") sunlight at different angles, the colors were separated.
However, he was not 100 percent sure of this inference. So Newton made another small change, this time with another prism to intercept these rainbow versions of light, and once the refracted light entered the new prism, they would recombine into a circular white beam. In other words, What a wonderful experimental technique Newton's ability to break a beam of white light into a different color and then reassemble it into white!
Conclusion: Sunlight is a mixture of all the colors in a rainbow that can be separated individually by the refraction of light.
Image: In 1665, Newton proved that sunlight is a mixture of all the colors in a rainbow, which can be separated by the refraction of light.
Paine's Starfish (1963-1969)
Hypothesis: If predators limit the number of species they prey on, the number of predators in this area increases after the elimination of the main predators.
Experiment: Ochre starfish (Pisaster ochraceus), also known as purple starfish, this creature has a good stomach malleability and feeds on mussels, caps, barnacles, snails and other unlucky victims. On some beach rocks (and tide pools) in Washington State, this starfish is the top predator.
Robert Paine also became a celebrity in the scientific community because of it. As an ecologist, Paine is fascinated by the role that top predators play in the environment. In June 1963, he launched an ambitious experiment in The Gulf of Nya, Washington. For a year, Paine intervened artificially to make all the purple starfish around the rocks along the coastline disappear.
It was a hard job, and Paine had to often use crowbars to pry the wayward starfish from various corners of the rock and then throw them into the sea.
Prior to the experiment, Paine had observed 15 different species of animal and algal ecology in the area he tested, and by June 1964, a year after he began cleaning starfish, that number had dropped to 8.
After the purple starfish disappeared, the number of barnacles soared, after which California mussels replaced these barnacles, and they began to dominate the entire terrain. These mussels covered the entire rocky area, thus expelling other species, making the rocky area no longer habitable for most of the former inhabitants: even sponges, sea anemones and algae, species that purple starfish did not eat, were expelled in large numbers.
All of these species continue to thrive on another stretch of coastline that Paine did not affect. Subsequent experiments convinced him that purple starfish were an important link in this ecology and that it had a great impact on the environment. After removing this species, the whole system becomes chaotic.
Conclusion: Top predators don't just affect the animals they hunt. Eliminating top predators can trigger a chain reaction that fundamentally alters entire ecosystems.
Image: After ecologist Robert Paine removed all starfish from the rocky area, he expected the number of mussels, barnacles, and slaves to increase, and he was wrong. JERRY KIRKHART/FLICKR (CC BY 2.0)
Finally, what's interesting?
Contrary to popular belief, Pavlov almost never used bells in his experiments, preferring to use metronomes, buzzers, organs, and electric shocks.
By Mark Mancini
Translation: Nuor
Reviewer: C&C
Original link:
https://science.howstuffworks.com/innovation/scientific-experiments/hypothesis.htm
The translated content represents the author's views only
Does not represent the position of the Institute of Physics, Chinese Academy of Sciences
Edit: zhenni