Home » Biology » Evolution



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

Examples of evolution

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

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

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

Using words carefully

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.

* 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.

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” express viewpoints, but are not based on facts or evidence. They cannot be disproved. 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. 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. (Example “Most women are bad drivers.”)  Unlike a belief, a prejudice is testable: it can be analyzed on the basis of facts.

To some extent, all people form some prejudices or accept them from others–family, friends, the media, etc.–without testing their truth. At best, prejudices are oversimplifications. At worst, they reflect a narrow-minded view of the world. 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 electrical 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 is what scientists call the 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 measure them, so there are no testable predictions. It is thus 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 (electrons) then electrons might move from one place to another.

We can measure electrical charges. That statement does makes testable predictions, so it is a good hypothesis.

cause of lightning electrical charges

C. 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.

Is evolution a theory or a fact?

One can say that the the word “evolution” refers to two distinct things. The ‘facts’ of evolution, and the ‘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 explicitly 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 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 that some organisms die before they reproduce. 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 directly observed in bacteria, some plants and some animals)

Here is the theory that connect such 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. So over time, some mutations become more common.

The “theory” of evolution is the relationship between observations (“facts.”)

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

Online Evolution Labs



Learning Standards

Massachusetts Science Frameworks Curriculum, Middle School

6.MS-LS4-1. Analyze and interpret evidence from the fossil record to describe organisms and their environment, extinctions, and changes to life forms throughout the history of
Earth. Clarification Statement: Examples of evidence include sets of fossils that indicate a specific type of environment, anatomical structures that indicate the function of an organism in the environment, and fossilized tracks that indicate behavior of organisms.

6.MS-LS4-2. Construct an argument using anatomical structures to support evolutionary
relationships among and between fossil organisms and modern organisms.
Clarification Statement: Evolutionary relationships include (a) some organisms have similar traits with similar functions because they were inherited from a common ancestor, (b) some organisms have similar traits that serve similar functions because they live in similar environments, and (c) some organisms have traits inherited from common ancestors that no longer serve their original function because their environments are different than their ancestors’ environments.

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.


1 Comment

Comments are closed.

%d bloggers like this: