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Chicken or the egg

Abiogenesis & spontaneous generation

Abiogenesis – modern discoveries

Charles Darwin’s Voyage of Discovery and Darwin’s notebook

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


Evolution of our kidneys

Evolution of humans

Evolution of whales

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

Advanced topics

Ontogeny and Phylogeny: Addressing misconceptions

Did nerves evolve twice?

Horizontal Gene Transfer and Kleptoplasty

Evolution and the 2nd law of thermodynamics

Scars of evolution

Two ideas related to evolution

Origin of Life (Abiogenesis) – how the very first living cells came into existence.

Evolution of Life – how cells multiplied, mutated, and developed into different types of cells.

Darwin’s Theory of Evolution mostly concerns itself with the second topic (evolution of life.) Darwin wrote little on abiogenesis.

Evolution 101

A Theory or a Fact?

The following has been loosely adapted from:

What Scientists Mean by “Fact,” “Hypothesis,” “Theory,” and “Law”

Colloquial (everyday English)

A fact is something that has really occurred, or is actually the case.
A hypothesis an idea about how something happened, an educated guess.
Colloquially, many people use the words “hypothesis” and “theory” to mean the same thing. That’s a problem because they are really very different.
A “phenomenon” is something amazing.

Scientific Use (How words are used in science)

Fact something that has really occurred or is actually the case.
Facts are true, justified beliefs
Hypothesis is a testable, proposed explanation for a phenomenon.
A phenomenon is any kind of observable or measurable occurrence in nature.
* 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.
A hypothesis must make a testable prediction. You could come up with an experiment that tests it, so you can find out if you were right or wrong.
Theory – A general rule that accurately describes many related phenomenon.
A theory is a relationship that has never been shown to be false, despite thousands of attempts by scientist to break it.

Distinguishing Fact, Opinion, Belief, and Prejudice

Adapted from Distinguishing Between Fact, Opinion, Belief, and Prejudice


are verifiable things that really occurred, or are actually true. We can determine whether it is true by researching, by examining evidence. This may involve numbers, dates, testimony, etc. (Ex.: “World War II ended in 1945.”) The truth of the fact is beyond argument if the measuring devices, or records, or memories, are correct. Facts provide crucial support for the assertion of an argument.

In science, a fact is a repeatable careful measurement (by experimentation or other means), also called empirical evidence. – Wikipedia

In history, a historical fact is a fact about the past. It answers the very basic question, “What happened?” Yet beyond merely listing the events in chronological order, historians try to discover why events happened, what circumstances contributed to their cause, what subsequent effects they had. – Norman Schulz

Facts by themselves are meaningless until we put them in context, draw conclusions, and, thus give them meaning.


are judgments based on facts. Opinions should be an honest attempt to draw a reasonable conclusion from factual evidence.

For example, we know that millions of people go without proper medical care, and so you form the opinion that the country should institute national health insurance even though it would cost billions of dollars.

An opinion should be changeable: in science, we are actually supposed to change our views if we have new evidence

By themselves, opinions have little power to convince. You must let your reader know what your evidence is, and how it led you to arrive at your opinion.


are convictions based on cultural or personal faith, morality, or values. Statements such as “Capital punishment is legalized murder” are sometimes called “opinions” because they express viewpoints, but they are not based on facts or other evidence. They cannot be disproved or even contested in a rational or logical manner. So technically, we wouldn’t call those positions “opinions”, but rather “beliefs.” Since beliefs are inarguable, they cannot serve as the thesis of a formal argument.

There is nothing wrong with having beliefs. We all have them – you do, I do. But we should be careful to distinguish between opinions and beliefs – or clearly explain to the reader what our view is, and what is based on. – RK


are half-baked opinions based on insufficient or unexamined evidence. (Ex.: “Most women are bad drivers.”) Unlike a belief, a prejudice is testable: it can be tested and disproved on the basis of facts. We often form prejudices or accept them from others–family, friends, the media, etc.–without questioning their meaning or testing their truth. At best, prejudices are careless oversimplifications. At worst, they reflect a narrow-minded view of the world. Most of all, they are not likely to win the confidence or agreement of your readers.

Scientific theories: Examples

Electricity – there are many different ways to create electrical sparks; many ways to create an electrical current, 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 phenomena are facts: the relationship between these facts is the theory.

Gravity – 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, a theory.


Good hypothesis vs bad hypothesis

A. Someone claims “lightning is caused by angry ghosts.”
If true then you’d predict that when ghosts are angry, there’d be more lightning.
But this can’t be tested.There is no way to determine whether ghosts are angry – or whether their wrath is correlated with thunderstorms.
We can’t even prove that ghosts exist.
That statement makes no testable predictions, so it is not a good hypothesis.
B. Someone claims “lightning is caused by electrical charges moving from the ground to the clouds.”
If true then you’d predict that when there is an imbalance of electrically charged particles (like electrons) then electrons might move from one place to another.
We can measure electrons and electrical charges.
That statement does makes testable predictions, so it is a good hypothesis.

cause of lightning electrical charges

A. Someone claims “Planets orbit the Sun at different speeds, because each planet has a different angel pushing it, and some angels are stronger than others.”
If its true then you’d predict that planets like Mercury are pushed by strong angels, and planets like Neptune are pushed by weak angels.
But this can’t be tested. There is no possible experiment that could determine whether angels are strong or weak.
You can’t even prove that they exist.
That statement makes no testable predictions, so it is not a good hypothesis.

B. Someone claims “Planets orbit the Sun at different speeds, because speed is related to the gravitational pull of the Sun, and the further away a planet from the Sun is, the less of a pull it feels.
If its true then you’d predict that planets like Mercury are pulled more, and move faster.
This can be tested. We do have ways to measure gravitational pull, distance from the Sun, and speed.
Since it makes testable predictions, it is a good hypothesis.

The facts & theory of evolution

Here are observable facts

* Many forms of life that used to exist, no longer exist today.
(We’ve found many fossils; more are discovered every day)
* Many forms of life exist now, that did not exist in the past.
(Many modern animals and plants are obviously different from fossils)

* DNA exists.

* Every time an organism reproduces, random changes (mutations) in DNA happen.
(We actually see these with gene sequencing)

* Some mutations help an organism survive – those genes pass on to the next generation.
(We actually see some organisms survive and reproduce. We can actually sequence the DNA of the parent and of the offspring. We literally see the genes.)

* Some mutations don’t help an organism survive; those genes die out.
(We actually see some organisms die before they reproduce. We actually see that their genes literally die with them.)

* Millions of different DNA samples show a relationship between all forms of life.

* As time goes by, some genes become more common, some become less common.
(This has been observed in bacteria, some plants and some animals)

The theory that connects the above noted facts

1. Organisms produce more offspring than can survive to adulthood and reproduce.

2. All organisms have random mutations.

3a. Mutations that allow an organism to survive are passed on to their offspring.

3b. Mutations that don’t allow an organism to survive die off.

4. Over time, favorable mutations become more common.

The “theory of evolution” is really just this relationship between observations (“facts.”)

In this sense, the theory is just as true as the theory of gravity, or the theory of electricity.

Peer review


Online Evolution Labs




“Let me try to make crystal clear what is established beyond reasonable doubt, and what needs further study, about evolution. Evolution as a process that has always gone on in the history of the earth can be doubted only by those who are ignorant of the evidence or are resistant to evidence, owing to emotional blocks or to plain bigotry.  By contrast, the mechanisms that bring evolution about certainly need study and clarification. There are no alternatives to evolution as history that can withstand critical examination. Yet we are constantly learning new and important facts about evolutionary mechanisms.”

– Theodosius Dobzhansky “Nothing in Biology Makes Sense Except in the Light of Evolution”,
American Biology Teacher vol. 35 (March 1973)  reprinted in
Evolution versus Creationism, J. Peter Zetterberg ed., ORYX Press, Phoenix AZ 1983

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