Evidence for Evolution Student Learning Guide (HS) (coming soon)
Evolution is the idea that living organisms are the modified descendants of pre-existing organisms. It’s the most important idea in biology, as was captured in a memorable quote by biologist Theodosius Dobzhansky: “Nothing in biology makes sense except in the light of evolution.”
What’s the evidence that evolution is true?
In what follows below and in the next three tutorials, we’ll look at the evidence supporting evolution. Because evolution is a scientific theory, let’s start by clarifying how the word theory is used in a scientific context.
2. A theory is much more than a hypothesis
In common speech, the word theory is often used in a way that’s synonymous with words like “opinion” or “belief.” For example, you’ve probably heard someone say something like: “That’s your theory. Let me tell you mine.”
That use of the word theory is closer to the scientific idea of a hypothesis. A hypothesis is an idea that requires testing. In science, a theory is an explanation that’s already been tested many times. Unlike a hypothesis, a theory is supported by a significant amount of evidence.
Any science student should be able to quote these definitions for how the words theory and hypothesis are used in a scientific context.
- Theory: An organized explanation of some aspect of the natural world that has been thoroughly tested and is well supported by evidence.
- Hypothesis: A unproven idea or explanation that you can test through study and experimentation. (adapted from Vocabulary.com)
To sharpen your ability to distinguish between a scientific theory and a hypothesis, read the following passages.
A theory explains a phenomenon, accounts for all available data, is supported by a huge body of evidence. Hypotheses are just guesses that need testing.
Adapted from: Ruth Levy Guyer, Professor of Immunology and Bioethics, Johns Hopkins University and Haverford College.
A theory is a well-established principle that has been developed to explain some aspect of the natural world…while a hypothesis makes a specific prediction about a specified set of circumstances. A theory has been extensively tested and is generally accepted, while a hypothesis is a speculative guess that has yet to be tested.
Adapted from Kendra Cherry, About.com, Introduction to Research Methods
Work on these flashcards until you can recite the definitions of theory and hypothesis above from memory.
3. Theory vs. Hypothesis Flashcards
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[h]Flashcards: Theory v. Hypothesis
Theory in science
A validated idea
Much more than a hunch
[a]A theory is an organized explanation of some aspect of the natural world that has been thoroughly tested and is well-supported by evidence.
[a]A hypothesis is an unproven idea or explanation that you can test through study and experimentation.
4. Theory vs. Hypothesis Quiz
Take the quiz below to make sure that this distinction between theory and hypothesis is clear.
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[h]Theory v. Hypothesis
[q]In the scientific method, the next step after posing an initial question or making an interesting observation is to formulate a testable
[q]In the 1800s, two German scientists proposed that all living things are composed of cells, and that cells are the fundamental units of life. During the past two hundred years, no living thing has ever been discovered that does not consist of cells. At this point, these ideas about cells are best understood as being a
[q]A specific and testable proposal that attempts to explain a limited set of observations is a
[q]Scientists are measuring the effect of a certain hormone on the growth of breast cancer cells. They think that this hormone might increase the growth of tumors. This is an example of a
[q]A proposed idea about the speed of falling objects was published by a scientist in the 1600s. Over the next centuries, this proposal was supported by a variety of experiments on earth, and by observations of objects in space. No observation refuting this idea has ever been made. At this point, this idea is best classified as a
[q]A well-substantiated explanation of some aspect of the natural world, based on a body of facts that have been repeatedly confirmed through observation and experiment.
[q]A group of students sets up an experiment to test the idea that tomato plants grown in blue light will produce larger fruit than tomatoes grown in regular sunlight. This idea would best be classified as a
[q]The idea that all infectious diseases are caused by germs (bacteria or viruses) has been repeatedly confirmed by hundreds of observations.
If you want to take this quiz again, click the button below
5. To prove evolution true, we need evidence of descent with modification
Darwin had a three-word phrase that, for him, summed up the process of evolution: descent with modification.
- Descent means “coming from an ancestor.”
- Modification means “change.”
Descent with modification means that over time, a population might change in ways so that the descendants are different from the ancestors. Or, if you run the clock backward, it means that the current form of a population (or an entire species) might be different from its ancestral form.
What’s the evidence that descent with modification has occurred? While much evolutionary change has occurred over vast expanses of time — thousands, millions, or even billions of years — we’ll see in the next tutorial, that there are many examples of evolutionary change that have been observed by humans in the years since Darwin wrote On the Origin of Species, in 1859. After that, we’ll look at evidence from the structure of living things, the fossil record, the distribution of living things on earth, and from the molecules that all living things are composed of.