Ah, but thatās the thing; A scientific theory IS a proven fact, and evolution is a very good example of an undeniably true one!
Iāve been meaning to write a post about what the meaning of a scientific theory is, and this seems like a good opportunity.
In science we have theories, and we have laws. Itās a very common misconception that a scientific theory is a an unproven hypothesis. This is understandable, but leads to a fundamental misunderstanding of how science works. A scientific theory isnāt the same as what we commonly refer to as a ātheoryā. Hereās a definition:
A scientific theory is a well-substantiated explanation of some aspect of the natural world that is acquired through the scientific method and repeatedly tested and confirmed through observation and experimentation. xĀ
Compare this to the definition of a scientific law:
A scientific law is a statement based on repeated experimental observations that describes some aspects of the universe. A scientific law always applies under the same conditions, and implies that there is a causal relationship involving its elements. x
This means, basically, that a law summarizes observations about some sort of natural phenomena (usually mathematically). A good example is Newtonās law of gravity!Ā
Newtonās Law of Gravity explains through mathematics how different bodies react to each other because of this force we call gravity, both on earth and in space, but it doesnāt explain why it happens or even what gravity actually is. No explanation, therefor a law!
Then we have theories, which not only document phenomena, but give explainations as to why these phenomena happen and what they are. A scientific theory requires more testable evidence than a law, and usually encompasses multiple laws and explains them more thoroughly. For example, Albert Einsteinās theory of relativity.
Newtonās law of gravity was testable, but it was only after Einstein proposed the theory of relativity that we started to understand what gravity actually is and how it functions. Einstein was able to give us explainations mathematically for why the laws of physics work as they do. Explanations for how it worked, therefor a theory!
(Itās also important to remember that a scientific theory and a scientific law are two very different things, and one can never become the other. A theory will always be a theory, and a law will always be a law.)
One of my favorite examples of this is the laws of Mendelian inheritance.Ā
Long before we knew what genetics were, farmers were breeding for favorable traits. They didnāt know where they came from or how they were passed from one organism to the next, but they knew that if they bred a large dog with another large dog, theyād get large puppies, and they knew that if they bred only their best produce that their plants would produce better produce in the future.
Gregor Johann Mendel started conducting experiments by hybridizing pea plants, and was able to prove that this consistently happened. By doing this he created three separate laws that all fall under the Laws of Inheritance; The Law of Segregation, the Law of Independent Assortment, and the Law of Dominance. It gets a little complicated here and Iām not an expert on DNA, but Iāll try to summarize.
The Law of Segregation states that all organisms contain two alleles for each trait, and that those separate during meiosis so each gamete only contains one of them. That means that offspring receives a pair of alleles from its parents for each trait, resulting in one allele for each trait from each parent. For example, a calico cat and a tabby may breed and produce 4 tabby kittens, but all of those kittens will also carry the genetic information of a calico.
The Law ofĀ IndependentĀ AssortmentĀ states that alleles for these traits are passed independently of one another during gamete formation. For example, if the calico is a manx and the tabby is a scottish fold, the kittens can inherit a short tail without inheriting their calico parents coloring. They can also look entirely like one parent despite carrying the genetic information of both. Each trait is passed independently of all other traits.
The Law of Dominance states that recessive alleles will be masked by dominant alleles. For example, blue eyes in cats is a recessive trait. Therefor even if the scottish fold has blue eyes (is a carrier and affected), the dominant trait eyes of the manx will determine the color of the kittens eyes, and weāll only have a slim chance of producing affected, blue eyed kittens if the manx also carries the recessive blue eyed gene, and those genes line up.
(If Iāve made any mistakes here, Iād appreciate someone with more knowledge on genetics letting me know)
But youāll notice he didnāt show how or why this happened, he was just able to observe it and prove that it did. It wasnāt until the Chromosome Theory of Inheritance was discovered that we could explain why. This was the theory that explained that chromosomes are what carry genetic material and pass these traits from one generation to the next.Ā
Itās a fundamental, unifying theory of genetics that shapes how we conduct our science today. This theory is the basis of genetic engineering, which has had a huge impact on modern science. Just for example, the manufacturing of drugs (insulin and vaccines!), gene therapy, the genetic engineering of lab animals, and, most famously, agriculture. AKA, GMOs.
This leads into another requirement of a theory; Being supported by numerous other fields of science. Genetics is one of the sciences that hugely supports the Theory of Evolution. This is how weāve been able to sequence DNA and discover how closely all life on earth is related, and how the DNA of humans and chimps is nearly identical.
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And this isnāt the only field of science that supports the validity of the Theory of Evolution.Ā
We have radioisotope dating! Isotopes make up all matter on earth, and by measuring the decay of radioactive isotopes, we can date rock layers. We can do this because we know the rate of radioactive decay. This is how we know that the Earth is around 4.5 billion years old. Weāve used this to date fossils and prove that transitional forms came between connected species, and that humans and modern animals didnāt live alongside dinosaurs.
We have paleontology! The fossil record shows extremely detailed evidence of evolution occurring. Evolution is so accurate in its predictions that thereās never been a single fossil found in a place that it shouldnāt be. For example, the transitional fossils between dinosaurs and modern birds is found right in the middle, exactly where weād expect it to be. So is the ancestor of platybelodon, and its relatives as they became our modern elephants!
Weāre able to predict so accurately where fossils should be located that weāve been able to pick sites to excavate based entirely on that, then find the fossils we expected! Predictive power is a huge part of a proven scientific theory.
We have molecular biology! Which proves that gene sequences among extremely different organisms are still related. The basic structure of all DNA on the planet is in the form of the double helix, and while we predictably have nearly all the same DNA as our primate cousins, over half of our DNA is also identical to banana plants!
Then we have embryology! When we compare embryos, not only are most animals nearly indistinguishable from each other, but we see holdover traits from our previous ancestors. The most compelling examples are the fact that human fetuses, and all other mammals, have gill slits as embryos. In mammals these develop into the eustachian tubes and the ear canal, while they continue to develop into gills in fish. Humans also have tails and yolk sacs as embryos! (Also look up lanugo in fetuses, very interesting and shared among other mammals)
Then thereās biochemistry! The basic chemistry that occurs in the cells of all life on earth is extremely similar, and shows that all modern organisms had a common ancestor. For example, all animals have enzymes and hormones. Trypsin is just one thatās found in everything from humans to sea sponges.
Then biogeography! The fact that groups of organisms that are related are all found near one another is more evidence for the validity of evolution. If life didnāt evolve, thereād be no reason for certain life to only exist on certain continents, or for species to be distributed in a pattern that reflects their genetic relationships with one another.
Modern observations are extremely helpful as well! This is why we now see antibiotic resistant strains of viruses, elephants becoming less likely to have tusks because of poaching, and the peppered moth becoming darker to better camouflage itself during the industrial revolution.
There are others, but Iāll end with comparative anatomy, which is one of the coolest, imo. (Iām probably biased because I collect bones lol)
When you compare the skeletal structures of vertebrates, we have extremely similar structures regardless of how wildly different our environments and behaviors are. The skeletal structure of a fin is hardly the best way for a fin to be designed, but because whales evolved from terrestrial mammals, they adapted using what they had. (we can also show the full evolution of cetaceans through the fossil record, which is very cool if you want to look it up.)
This is true in non-mammals as well. An excellent example is the laryngeal nerve! In fish, the nerve makes a direct line from the brain down to the larynx, which is practical and to be expected. In animals that developed longer necks, however, we see that the nerve is trapped under the aortic arch!
The nerve had to evolve with us as we evolved from our aquatic ancestors, so our laryngeal nerve is forced to not go from our brain to our larynx, but rather to take a detour into our chest and around the aortic arch before doubling back!Ā
This is amazing in giraffes, where the nerve is nearly 15 feet long because it was forced to grow as the giraffeās neck did, and now takes a detour down the entirety of the giraffeās neck and around the heart before returning the the larynx, which was its destination.
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There are mountains more evidence, but itād take a lifetime to cover it all.
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So youāve got the way a theory works a little backwards; A theory only remains a theory when it canāt be disproven, and therefor is proven accurate. For a theory to be a theory, it has to be proven true. This is why we teach other theories, for example:
Plate tectonics theory: Plate tectonics is the theory that the outer rigid layer of the earth (the lithosphere) is divided into a couple of dozen āplatesā that move around across the earthās surface relative to each other, like slabs of ice on a lake.
Cell theory: In biology, cell theory is a scientific theory which describes the properties of cells. These cells are the basic unit of structure in all organisms and also the basic unit of reproduction.
and
Atomic theory: In chemistry and physics, atomic theory is a scientific theory of the nature of matter, which states that matter is composed of discrete units called atoms.
In your tags you state that evolution is a theory, and therefor canāt be taught as fact. Iām sure you donāt believe that we shouldnāt teach about the existence of atoms and the function of cells because theyāre āonly theoryā, so I hope this makes clearer why that notion is flawed. We accept all of these as true because we know factually that they are.Ā
The reason that evolution is given such intense scrutiny is because it disproves the notion that humans are a separate, superior entity to all other life on earth. This is a blow to some egos and contradicts some peopleās religious beliefs. The discovery that Earth wasnāt the center of our solar system, much less the universe, was met with the same sort of scrutiny for the same reasons. The ever building proof that weāre only a tiny flicker of what has been and will be in the universe inspires strong reactions in people, for good or bad. Personally, I find it endlessly interesting!
Also, to clarify, attempting continually to disprove a theory wouldnāt necessarily be good science. When you have a theory like plate tectonics, trying to disprove it at this point really isnāt a good use of your time. We know how it works, weāve seen it working, we can predict how itāll work, we can prove this is how mountains formed and earthquakes happen and continents drift. Being critical and making sure things line up properly is good science, but trying to continuously disprove something we know to be fact is a waste of energy and resources.
Evolutionary theory is the basis of everything from vaccines and Glofish to agriculture, modern medicine and decoding DNA. Itās so ingrained in everything that we do, that itās vital for people to understand how it works.Ā
If it were proven false tomorrow, itād take a lot of other fields of science down with it. But most of us are understandably doubtful that itāll happen, because itās been undergoing this same intense scrutiny since Darwin published The Origin of Species in 1859. Thatās an awfully long time and a lot of scientific advances for there to have never been a single, solitary piece of evidence that disproved it.
To stay on theme, letās end with a platybelodon family reunion.
