Evolution is a fact, and evolution is more than a fact. Evolution is more than just an
observable reality. Evolution is more than these things because evolutionary models and
explanations are the cornerstones of biological science. Evolution is the scaffold and the
remarkable foundation for understanding our biological world and our biological self.
To better understand what I mean, we need to discuss the term "theory," as in "evolutionary
theory." In everyday speech we use the word theory very differently from how we use the
term theory in science. Theory in everyday speech is basically a hunch. As a fun example,
let's discuss the Scottish cuisine known as haggis. Now if you've never had this delicacy,
let me explain--haggis is a pudding. Okay, so far, so good. I personally appreciate pudding.
In fact, my appreciation for pudding rivals that of Bill Cosby's, but haggis is not that
type of pudding. Haggis is pudding made from sheep's liver, heart, and lungs, which is
then simmered inside the animal's own stomach. Now you're not going to see that flavor of
pudding pop anytime soon. So given that context, the comedian Mike Myers once cleverly stated,
and I quote, "My theory is that all of Scottish cuisine is based on a dare. I can certainly
see my friends daring each other to eat something like that." And Mr. Myers's use of the term
theory is normal for everyday speech. Clearly, our use of the term theory in everyday speech
is very flexible. We can use it for humor. We can use it for an honest hunch, for how
things work, but in science a theory means something much more specific. A scientific
theory is a well-substantiated model, often an explanation, which has been repeatedly
confirmed by a large body of experiments and observations. Most scientific theories are
so well substantiated in science that they are essentially established facts. For example,
a spherical earth is a theory. It is also an accepted fact. A spherical Earth explains
a large body of observations. Just a few examples: a spherical Earth explains why the Earth forms
a curved shadow on the Moon, and how the Earth can look like a disk from space regardless
of which side of the Earth is being observed, how we can traverse the globe, and how satellites
can orbit. For these and many other reasons, we now accept a spherical Earth as true. And
because Spherical Earth Theory is so well substantiated, it has earned our trust. We
can use the theory as a framework for impacting our lives in predictable ways, whether it
being laying a cable for transcontinental communications or predicting the spread of
the next year's flu virus. Because spherical Earth is a valid scientific theory, we can
use it. What's important to understand is evolutionary theory is as substantiated as
spherical Earth theory, and for that reason, evolutionary theory is empowering. While we
can only give a few examples in this course, I hope this catalyzes some excitement in you
to understand evolution more fully. Evolution is part of our physical reality. It is part
of our world, and as famously stated by biologist Theodosius Dobzhansky, "Nothing in biology
makes sense except in the light of evolution." While evolutionary theory is a framework by
which we understand evolution, evolution itself is an observation. That is, evolution is a
phenomenon that can be directly observed, and it's a fact. At the most basic level,
evolution refers to the fact that there is change in the frequencies of inherited traits
over generations. Nothing about this should be overly surprising. We know that parents
pass down some of their genetic traits to their children, and clearly over time some
new traits emerge, and for various reasons some traits never get passed down. This change
in the inherited traits over time is evolution. That's why evolution as a phenomenon is an
observable fact. It happens. What's interesting is when we crank up time. As we crank up time,
this relatively subtle observation will lead to remarkable biological diversity.