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What are we learning?

The diversity and unity of life on Earth can be explained by the process of evolution. Over time, the process of natural selection leads to both the extinction of existing species and the evolution of new species.

Why are we learning this?

Excerpted from Teaching About Evolution and the Nature of Science (1998) National Academy of Sciences

Evolution accounts for the most fundamental features of the world around us: the similarities among living things, the diversity of life, and many features of the physical world we inhabit. Explanations of these phenomena in terms of evolution draw on results from physics, chemistry, geology, many areas of biology, and other sciences. Thus, evolution is the central organizing principle that biologists use to understand the world. To teach biology without explaining evolution deprives students of a powerful concept that brings great order and coherence to our understanding of life.


Abiogenesis – how the very first living cells came into existence.

Evolution  – how cells (and later organisms) changed over time.

Darwin’s theory of evolution mostly concerns itself with the second topic. He wrote very little on abiogenesis.


Abiogenesis & spontaneous generation  – how the very first living cells came into existence.

Abiogenesis – modern discoveries

Charles Darwin’s Voyage of Discovery

Darwin’s finches

Fossils: Evidence of evolution over time and Dating of fossils

Convergent evolution and Homologous and analogous structures

Natural selection

Artificial selection

clades & phylogenies

clades rotate = equivalent phylogenies

Gradualism vs. Punctuated Equilibrium

Is evolution a theory or a fact?

Examples of evolution

Chicken or the egg


Evolution of our kidneys

Evolution of humans

Evolution of whales

Evolution of turtles from early reptiles

Where did the idea of evolution develop? How has the idea of evolution changed over time?

Mollusk family tree

Advanced topics

Distinguishing Fact, Opinion, Belief, and Prejudice

Darwin’s notebook

Evolution of the first animals

Ontogeny and Phylogeny: Addressing misconceptions

Did nerves evolve twice?

Horizontal Gene Transfer and Kleptoplasty

Evolution and the 2nd law of thermodynamics

Scars of evolution

A timescale for the origin and evolution of all of life on Earth

Using words carefully: Colloquial vs scientific use

Colloquial (everyday English)

fact is something that has really occurred, or is actually the case.
A hypothesis an idea about how something happened, an educated guess.
A phenomenon is something amazing.

Scientific Use

A fact is something that has really occurred or is actually the case.
Facts are true, justified beliefs.

A hypothesis is a testable, proposed explanation for a phenomenon.

phenomenon is any kind of observable or measurable occurrence in nature.

What are some examples of phenomenon?

* When water gets hot enough it boils; that’s a phenomenon.
* When a rock is dropped, gravity pulls it down, faster and faster; that’s a phenomenon.
* When you pluck a guitar string, it vibrates and creates a musical sound; that’s a phenomenon.

But evolution is “just a theory”

When scientists describe “the theory of evolution” they are using the word “theory” in a very precise way,  in the same way we talk about the theory of electricity and the theory of gravity – and no one denies that electrical phenomenon or gravitation are real.

For scientists, a theory is a logical structure that ties together a vast array of known, measurable facts, into a single equation or brief, logical concept. Consider

Electromagnetic theory

 There are many different ways to create electrical sparks; electrical currents, and millions of different devices (and living beings) that use electricity. Yet all this can be described using just four math equations – they describe all behaviors of electricity.

Together these equations (Maxwell’s equations) are the theory of electricity. Electricity is real. It’s not “just a theory”.

The existence of these electrical phenomena are facts: the relationship between these facts is the theory.

 Gravitational theory

Every time you drop an object, it falls. The longer it falls, the faster it goes (unless something like air resistance slows it down). That’s not just true here on Earth – objects are also pulled down by gravity on the moon, Mars, and asteroids. Even the Sun has gravity.  There are millions of different objects that respond to the pull of gravity on Earth.

Yet all his can be described using just one math equation, Newton‘s theory of universal gravitation.
Newton's universal law of gravitation Earth Moon

A rock falling is real; a planet orbiting the Sun is real. That’s not “just a theory”.

The existence of these phenomena are facts: the relationship between these facts is what scientists call the theory.

Resources and Evolution Labs

Evolution 101. Univ of California Museum of Paleontology




Example questions

Feb 2016 MCAS.  Scientists often compare fossils of extinct organisms with living organisms to help determine evolutionary relationships. What is the primary information that scientists use when comparing fossils with living organisms?
A. the types of minerals that formed the fossils
B. the size of the rocks that contained the fossils
C. the cause of death for the fossilized organisms
D. the physical characteristics of the fossilized organisms


Feb 2016 MCAS . The pictures below show the shells of some species of land snails found on a Pacific island. Each species was found on a different hill on the island. Based on the snails’ shell shapes, scientists made hypotheses about the evolutionary relationships among the snails. Which of the following would be the best characteristic to compare in order to test these hypotheses?

Snail shells 16

A. the size of the snails
B. the diet of the snails
C. the DNA of the snails
D. the average age of the snails


Scientists hypothesized that several species of frogs called tiger frogs evolved from a recent common ancestor. The hypothesis was based on fossil
evidence and on physical similarities among living species. Which of the following provides the best additional support for the scientists’ hypothesis?

A. Tiger frogs have longer life spans than other frog species.
B. Tiger frogs have the same diet and all use enzymes to digest food.
C. Tiger frogs live near each other and are all preyed upon by the same predator species.
D. Tiger frogs have similarities in their mitochondrial DNA that are not shared by other frog species.


Learning Standards

Massachusetts Science Frameworks Curriculum, Middle School

8.MS-LS4-4. Use a model to describe the process of natural selection, in which genetic variations of some traits in a population increase some individuals’ likelihood of surviving and reproducing in a changing environment. Provide evidence that natural selection occurs over many generations. Clarification Statements: The model should include simple probability statements and proportional reasoning. Examples of evidence can include Darwin’s finches, necks of giraffes, and peppered moths.

8.MS-LS4-5. Synthesize and communicate information about artificial selection, or the ways in which humans have changed the inheritance of desired traits in organisms. Clarification Statement: Emphasis is on the influence of humans on genetic outcomes in artificial selection (such as genetic modification, animal husbandry, and gene therapy).

Massachusetts Science Frameworks Curriculum, High School

HS-LS4-1. Communicate scientific information that common ancestry and biological evolution are supported by multiple lines of empirical evidence, including molecular,  anatomical, and developmental similarities inherited from a common ancestor (homologies), seen through fossils and laboratory and field observations.

HS-LS4-2. Construct an explanation based on evidence that Darwin’s theory of evolution by natural selection occurs in a population when the following conditions are met: (a) more offspring are produced than can be supported by the environment, (b) there is heritable variation among individuals, and (c) some of these variations lead to differential fitness among individuals as some individuals are better able to compete
for limited resources than others.

HS-LS4-4. Research and communicate information about key features of viruses and bacteria to explain their ability to adapt and reproduce in a wide variety of environments.

HS-LS4-5. Evaluate models that demonstrate how changes in an environment may result in the evolution of a population of a given species, the emergence of new species over generations, or the extinction of other species due to the processes of genetic drift,
gene flow, mutation, and natural selection.


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