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It’s easy to forget that what seems obvious to us today, thanks to centuries of shared knowledge, wasn’t always self-evident. The very fact that we take certain things for granted is part of what makes their origins so fascinating. We've already explored milestones in law, medicine, and astronomy, so now let's turn our attention to biology.
10. The Discovery That Animals Can Become Extinct
If you happened upon a fossil while strolling on the beach, you’d naturally think it belonged to a species that no longer exists. The notion of species vanishing has become so commonplace that it's hard to imagine a time when people believed all creatures were still out there somewhere. The prevailing belief was that God had created everything—why would He make something that wasn’t meant to survive?
Georges Cuvier was the first to challenge this idea. In 1796, he published a paper on elephants, detailing the African and Asian subspecies. He also referenced a third type, known only through its skeletal remains. Cuvier pointed out distinct differences in the shape of the jaw from this third elephant and proposed it was a separate species altogether. He named it the mastodon, but where were the living specimens?
Cuvier stated: “All of these facts, consistent among themselves, and not contradicted by any report, seem to me to prove the existence of a world before ours, destroyed by some kind of catastrophe.” But he didn’t stop there. Cuvier also studied ancient vertebrate fossils—coining the term 'Pterodactyl'—and deduced that reptiles had once been the dominant life form.
9. The First Cells Cultured Outside The Body
For biologists researching the inner workings of animal cells, it's far easier when those cells are no longer part of the living animal. Today, scientists culture a wide variety of cells in vitro, enhancing our understanding of life. The first person to succeed in keeping cells alive outside of a host was Wilhelm Roux, a German zoologist. In 1885, he placed part of a chicken embryo in a saline solution and kept it alive for several days.
Research on keeping tissue alive continued for several decades, but it wasn’t until 1907 that scientists were able to grow new cells in solution. Ross Harrison took tissue from frog embryos and succeeded in growing new nerve fibers, which he managed to keep alive for a month. Today, cell lines can be maintained indefinitely—scientists are still working with lines derived from a woman who passed away over 50 years ago.
8. The Discovery of Homeostasis
You likely learned about homeostasis in school, but it’s easy to forget its significance. Homeostasis is one of the four core principles of modern biology, alongside evolution, genetics, and cell theory. In essence, it’s the idea that organisms regulate their internal environment. While it sounds simple—like objects with mass attract each other, the Earth orbits the Sun, or there is no spoon—it’s actually a profound realization about the nature of life.
The concept of homeostasis was introduced by Claude Bernard, a prolific 19th-century scientist who was as famous as Louis Pasteur (the two were even friends). Bernard made major contributions to our understanding of physiology, but his passion for vivisection cost him his first marriage, with his wife later campaigning against his work. Nevertheless, homeostasis—which he termed 'milieu intérieur'—was not fully appreciated for its significance until long after Bernard’s death.
In an 1887 lecture, Bernard elaborated on his theory: “The living body, though it is dependent on its surrounding environment, remains relatively independent of it. This independence comes from the fact that in living organisms, the tissues are shielded from direct external influences and are safeguarded by a true internal environment, particularly the fluids that circulate within the body.”
A scientist who is ahead of their time often goes unrecognized, but Bernard’s other groundbreaking contributions ensured his place in history. However, it wasn’t until 50 years later that science was ready to test, confirm, and fully appreciate his most important concept. His 1911 entry in *Encyclopedia Britannica* made no mention of homeostasis. Sixty years later, the same publication hailed it as his 'most seminal contribution.'
7. The First Isolation of an Enzyme
You’ve probably learned about enzymes in school, but in case it’s been a while, they are large proteins that facilitate chemical reactions. Among other things, they help make really effective washing powder. They also drive tens of thousands of chemical reactions in living organisms (many of which lead to the stains that washing powder is made for). Enzymes are as essential to life as DNA—our genetic material cannot replicate itself without them.
The first enzyme to be discovered was amylase, also known as diastase, which is present in your mouth right now. It breaks down starch into sugar and was first identified by French industrial chemist Anselme Payen in 1833. Payen concentrated the enzyme, but the mixture remained impure. For many years, biologists believed that extracting a pure enzyme would be impossible.
It took nearly 100 years for American chemist James Batcheller Sumner to prove the doubters wrong. In the early 1920s, Sumner set out to isolate an enzyme. His goal was so ambitious that it caused him to lose a scholarship with one of the leading experts in the field, who dismissed the plan as foolish. But Sumner persisted, and in 1926, he isolated urease, an enzyme that breaks down urea into its chemical components. Many of his colleagues questioned his results for years, but they were eventually forced to accept them. Sumner's groundbreaking work earned him the Nobel Prize in 1946.
6. The Idea That All Life Shares A Common Ancestor
Who was the first person to suggest that all life evolved from a single organism? Many of you would likely answer, “Charles Darwin.” While it’s true that Darwin proposed this idea—one of the most memorable quotes from *On the Origin of Species* is: “There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one.” However, the concept of a common ancestor was actually first introduced decades earlier.
In 1740, Pierre Louis Moreau de Maupertuis, a man with a name that could not be more French, proposed that 'blind destiny' might have led to the creation of a wide variety of individuals, with only the most capable surviving. In 1790, Immanuel Kant suggested that this theory could imply a single original ancestor of life. Five years later, Erasmus Darwin wrote: 'Would it be too bold to imagine, that all warm-blooded animals have arisen from one living filament?' His grandson, Charles, decided it wasn’t bold at all.
5. The Development of Staining
If you’ve ever seen microscope images of cells (or looked at them yourself), chances are they were stained beforehand. Staining enables us to see parts of cells that are otherwise invisible and enhances the clarity of what we can see. There are numerous different staining techniques available, making it one of the most essential methods in microbiology.
The first person to stain a sample for microscope examination was Jan Swammerdam, a Dutch naturalist. Swammerdam, best known for discovering red blood cells, dedicated his career to observing virtually everything under a microscope. In the 1680s, he wrote about using 'coloured liqueurs' on dissected worms 'to better distinguish their internal parts, which are all of the same colour.'
Unfortunately for Swammerdam, the text wasn’t published until 50 years later, by which point he had already passed away. Meanwhile, his fellow Dutch naturalist, Antonie van Leeuwenhoek, had independently come up with the same idea. In 1719, Leeuwenhoek used saffron to stain muscle fibers for examination, and he is often regarded as the pioneer of this technique. Since both men arrived at the same conclusion and both earned reputations as microscopy pioneers, there's really no need to feel bad about either outcome.
4. The Emergence of Cell Theory
'Every living creature is made of cells' is a statement that would probably be met with less disagreement than 'the Earth is not flat.' Though we take cell theory for granted today, the idea didn’t actually emerge until the 19th century, about 150 years after Robert Hooke first observed cells through a microscope. In 1824, Henri Durochet wrote about the cell: 'It is clear that it constitutes the basic unit of the organized state; indeed, everything is ultimately derived from the cell'—though he wrote it in French.
In addition to cells being the fundamental unit of life, cell theory also asserts that new cells form when a pre-existing cell divides. Durochet missed this part, believing new cells formed within their parent. The first realization that cells divide to reproduce belongs to another French scientist, Barthelemy Dumortier, though many others contributed to the theory's development. While certain theories can be attributed to a single person—such as Newton, Galileo, Darwin, and Einstein—cell theory isn't one of them. It developed through the collective contributions of many, in the same way modern science progresses.
3. The Discrediting of Preformationism
One of the more bizarre ideas in history was preformationism, once a dominant theory on how babies were created. As the name suggests, it proposed that all creatures were pre-formed—meaning that their shape existed before development even began. In essence, it was believed that a miniature human being existed inside either the sperm or egg, awaiting its opportunity to grow. This tiny person was called a homunculus.
One of the major advocates of preformationism was Jan Swammerdam, the same individual who invented staining techniques mentioned earlier. This idea was widespread for over a century, from the mid-17th century through to the late 18th century.
The counterpart to preformationism is epigenesis, which suggests that life unfolds through a series of processes. The first person to propose this theory, in opposition to the prevailing belief in preformationism, was Caspar Friedrich Wolff. In 1759, he wrote a paper explaining that embryonic development began with a layer of cells. His work was controversial at the time, but as microscopes improved, his theories became more widely accepted. By the 19th century, preformationism was effectively discredited.
2. The Identification of Viruses
In the 1860s, Louis Pasteur gained renown for his germ theory of disease, which changed the way we understand infections. However, his work only covered part of the story. Early advocates of germ theory believed that all infectious diseases were caused by bacteria. Yet, the common cold, influenza, HIV, and many other diseases are caused by a completely different agent—viruses.
Martinus Beijerinck was the scientist who first recognized that bacteria weren’t the entire explanation. In 1898, he used sap from tobacco plants infected with mosaic disease. He passed the sap through a filter fine enough to remove all bacteria. When Beijerinck applied the filtered sap to healthy plants, they still fell ill. Repeating the experiment, he found that the contagion remained. He concluded that something else, possibly a liquid, was responsible. He named this agent contagium vivum fluidum, or the soluble living germ.
Beijerinck also revived the old English term 'virus' to describe this mysterious agent. The revelation that viruses were not liquids was made by an American scientist named Wendell Stanley. It took some time—Stanley wasn’t even born until 1904, six years after Beijerinck’s discovery. For his work on viruses, Stanley was awarded the 1946 Nobel Prize in Chemistry, shared with James Sumner, who was honored for his enzyme research.
1. Decoding DNA
Until his recent passing, British scientist Frederick Sanger held the rare distinction of being the only person to have won two Nobel Prizes while alive. It was his work behind his second Nobel that secured his place on this list (a recognition that’s nearly as prestigious). In 1980, Sanger shared the Nobel Prize with American biochemist Walter Gilbert. The duo had jointly published a method in 1977 for determining the sequence of the building blocks that make up a strand of DNA.
The importance of this breakthrough is clear in how quickly the Nobel committee honored them. Sanger’s method ultimately proved to be both more affordable and simpler, and it became the gold standard for DNA sequencing for a quarter of a century. The distinctive columns of unevenly spaced lanes that result from Sanger’s method are instantly recognizable in DNA tests. Through this invention, Sanger helped launch revolutions in criminal justice, evolutionary biology, medicine, and beyond.
