[Under Construction]

Darwin's Theory of Evolution by Natural Selection

(Problems it solved, core elements included by Darwin, modern refinements and applications, suggestions for thinking about what it means to you)

Question: How do we explain the disappearance of life forms, the appearance of new life forms, and the similarities, connections and gaps among life forms alive today and observed in the fossil record? What is the process by which these things occur?

Introduction

Darwin's original theory of evolution by natural selection (On the Origin of Species by Means of Natural Selection,1859) has provided a very successful framework for making sense out of a wide range of observations. Today the theory of DNA-based evolution is a well-tested and core part of modern biology, anchored by threads of evidence connecting it to nearly every area of human knowledge. It is possible that new discoveries may lead to future changes in the details of the theory. But the basic ideas are essential to the concrete successes in agriculture, medicine, genetic engineering and ecology that we have come to take for granted, and they form a coherent timeline that is interwoven with evidence from diverse fields such as geology, astronomy, archaeology, etc. Just as we can't throw out our basic theory of electrons, for example, without denying most of our everyday computer technology, we also need the core elements of the theory of evolution in order to explain applications that now permeate our society.

Within this basic framework of evolution there is much room for creativity and difference of opinion in making meaning out of the facts. But it's important to be familiar with the basic pillars of the scientific knowledge - this knowledge enriches and constrains our perception of ourselves, and it’s difficult to see how we can build a very realistic understanding of who we are and where we come from without taking these insights into account in some way. Even if we want to argue that the observations are misleading in some way, we still need to acknowledge them and provide some coherent explanation for what we see in the world. So that's our aim here: to provide an overview of what is solidly known, to give you the basic material and encourage you to think about how you want to interpret it and make meaning for yourself within this framework.

What is a Theory?

In referring to a scientific theory, the word theory means a well tested, coherent explanation of a set of observations about nature. Examples are the theory of gravity, theory of relativity, heliocentric theory, microbe theory of disease, etc. Each is a basic set of concepts that explains what we see in a way that matches with observations and experiments so far. We apply these theories in our daily lives and many things we take for granted function on the basis of the theories.

When we first propose an explanation for what we see, we call it an hypothesis - then we make predictions based on the hypothesis, and if it passes some tests that don't refute the hypothesis, it becomes better established as a theory. So a theory is an hypothesis that has been well tested and has failed to be refuted or falsified. (Give examples of suggesting an hypothesis and gathering information to test it: cause of illness - food poisoning vs. flu, etc.)

A scientific theory must be capable of being refuted or falsified - science progresses by trying to prove a theory wrong. It's hard to prove that your theory is definitely the right explanation. It's always possible that in new new circumstances, your theory will no longer make the correct prediction. So you can never prove a particular theory right, but you can prove that it needs to be modified. All you need is one observation that contradicts a prediction of the theory. (Think about our unknown object lab - without opening it, you never knew absolutely for sure what was in the box, but you could disprove a suggestion by finding an observation that was inconsistent with your idea of what the object was).

Also note that you don't have to prove a theory is absolutely true in all its details, in order for it to work and be very useful.(eg Newtonian gravity)

Other traits of a good theory:

Resources:

Background Context

- geology and astronomy (ages as known in Darwin's time - Charles Lyell, etc. - compared to what we know now: earth about 4.5 billion years old, known universe about 14 billion years old, life cycles of stars, ages based on radioactive elements, etc. All fits together pretty well.)

- Timeline of the history of the universe.(express in terms of human lifespans to give some perspective on how much time we have to work with) Also http://www.pbs.org/wgbh/evolution/change/deeptime/index.html

- wide variation of types of organisms, connections between the different species, gaps in fossil record

- problem of extinction - why are some things seen in the fossil record not seen alive now?

Basic ideas of Darwin - The Origin of Species

Species change through natural selection:

Note that Darwin did not have an understanding of the actual unit of heredity - he postulated that there must be such a mechanism. Only later did Mendel show how traits could be passed on from one generation to the next, and only much later (Watson and Crick) did we gain an understanding of DNA as the specific means of passing on traits.

Resources:

Modern Developments and Insights

Examples:

Resources:

Interpretations and Implications

Social and political applications and misapplications (social darwinism, etc.)

Great Story web site - modern thoughts on reconciling evolutionary biology and religious traditions

Craig's notes on evolution