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Mind-bending, counterintuitive facts sometimes unlock deeper levels of understanding
Despite having more cells, most large animals — such as elephants — do not develop cancer at higher rates than smaller animals, such as mice. This fact puzzled biologists and was called Peto’s paradox. Studying this paradox eventually led scientists to a deeper understanding of cancer biology.
Vicki Jauron, Babylon and Beyond Photography/Getty Images
By Katie Grace Carpenter

A paradox is when a scenario seems — at first — impossible. It goes against what your gut feeling tells you is true. Once resolved, however, a paradox often reveals something crucial about how a system works. It may correct a common misconception. Or it may address incorrect assumptions.
Sometimes, a paradox consists of real facts that seem to defy expectation. Moravec’s paradox is one example. It notes that many abilities that come easily to humans are quite hard to program into a robot. Walking, for instance. On the flip side, many easy-to-program abilities, such as complex math, are hard for humans to learn. Exploring this paradox can help us better understand how the human mind works.
Peto’s paradox is another example. It points out that large, long-lived animals get cancer at about the same rate as small, short-lived ones. For a long time, that fact puzzled scientists. They expected large animals to get cancer more often. Cancer starts when something goes wrong with a single cell’s genetic material. Shouldn’t large animals — which contain many more cells — have this problem much more often than small ones? The data showed this was not the case.
Scientists studied this paradox. They learned that large animals have genes that help reduce cancer risks. Researchers did not know to look for such genes before noticing the paradox. This is one case of a paradox helping us learn things we didn’t know that we didn’t know.
Some paradoxes are thought experiments. That’s an imaginary scenario that allows us to explore an idea that we can’t test in real life. Imagine, for instance, you traveled to the distant past. But then, you accidentally killed a distant ancestor. (Oops!) This might mean that you would no longer be born. But wait. If you no longer exist, that means you wouldn’t be able to travel back in time to kill your ancestor in the first place, right?  
On its own, this sci-fi paradox doesn’t answer questions. But it does help us think about the physics of time. And that can inspire new ideas in scientists who study the nature of our universe.
The “paradox of horror” refers to how people often seek out films that seem — on first glance — to evoke only negative emotions.
Check out the full list of Scientists Say.
ancestor: A predecessor. It could be a family forebear, such as a parent, grandparent or great-great-great grandparent. Or it could be a species, genus, family or other order of organisms from which some later one evolved. For instance, ancient dinosaurs are the ancestors of today’s birds. (antonym: descendant)
cancer: Any of more than 100 different diseases, each characterized by the rapid, uncontrolled growth of abnormal cells. The development and growth of cancers, also known as malignancies, can lead to tumors, pain and death.
cell: (in biology) The smallest structural and functional unit of an organism. Typically too small to see with the unaided eye, it consists of a watery fluid surrounded by a membrane or wall. Depending on their size, animals are made of anywhere from thousands to trillions of cells. Most organisms, such as yeasts, molds, bacteria and some algae, are composed of only one cell.
data: Facts and/or statistics collected together for analysis but not necessarily organized in a way that gives them meaning. For digital information (the type stored by computers), those data typically are numbers stored in a binary code, portrayed as strings of zeros and ones.
gene: (adj. genetic) A segment of DNA that codes, or holds instructions, for a cell’s production of a protein. Offspring inherit genes from their parents. Genes influence how an organism looks and behaves.
genetic: Having to do with chromosomes, DNA and the genes contained within DNA. The field of science dealing with these biological instructions is known as genetics. People who work in this field are geneticists.
paradox: An idea or a statement that is true, but that seems logically impossible.
physics: The scientific study of the nature and properties of matter and energy. Classical physics is an explanation of the nature and properties of matter and energy that relies on descriptions such as Newton’s laws of motion. Quantum physics, a field of study that emerged later, is a more accurate way of explaining the tiny motions and behavior of matter about the size of electrons. A scientist who works in such areas is known as a physicist.
risk: The chance or mathematical likelihood that some bad thing might happen. For instance, exposure to radiation poses a risk of cancer. Or the hazard — or peril — itself. (For instance: Among cancer risks that the people faced were radiation and drinking water tainted with arsenic.)
robot: A machine that can sense its environment, process information and respond with specific actions. Some robots can act without any human input, while others are guided by a human.
scenario: A possible (or likely) sequence of events and how they might play out.
system: A network of parts that together work to achieve some function. For instance, the blood, vessels and heart are primary components of the human body’s circulatory system. Similarly, trains, platforms, tracks, roadway signals and overpasses are among the potential components of a nation’s railway system. System can even be applied to the processes or ideas that are part of some method or ordered set of procedures for getting a task done.
thought experiments: Mathematical analyses of ideas, situations or events. They are not based on real-world tests in a lab or the environment. They instead use numbers and relationships between mathematical operations to test whether something can or will happen. This is also known as theoretical research.
universe: The entire cosmos: All things that exist throughout space and time. It has been expanding since its formation during an event known as the Big Bang, some 13.8 billion years ago (give or take a few hundred million years).
Katie Grace Carpenter is a science writer and curriculum developer, with degrees in biology and biogeochemistry. She also writes science fiction and creates science videos. Katie lives in the U.S. but also spends time in Sweden with her husband, who’s a chef.
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