Introduction

Chapter 1 of your textbook includes the following:

Science is "a systematic process for learning about the world and testing our understanding of it.” A few paragraphs later it says, "Scientists examine ideas about how the world works by designing tests to determine whether these ideas are supported by evidence."

The process of natural selection, first proposed by Charles Darwin in 1859, is one of the primary agents of evolution. The concept of natural selection is not difficult to grasp. In fact, Stephen Gould of Harvard University described it simply as two undeniable facts and one inescapable conclusion.

1. First, all individuals of a species are variable (different from one another) and these variations are inheritable.
2. Second, all individuals produce more offspring than can survive to reproduce.

I like to paraphrase these as:

1. Variation exists.
2. Death happens.

Some more explanation:

• No matter how similar two squirrels on campus happen to look to you they are each unique. Some have bigger ears, others have little pinkie toes, some have a slow metabolism. There are two obvious exceptions: identical twins and organisms that reproduce as clones. We'll ignore these exceptions for this lab.
• To be important to natural selection these differences must be caused by genetics so that they are passed on to one's offspring. If a fish is tiny because it has been starved most of its life it won't necessarily have small offspring. If it is small because it produces 1/10 the normal amount of growth hormone this is a characteristic that will be passed on.
• Many of us hope to die a peaceful death after a long productive and healthy life. That isn't the type of death refered to here. We're talking about the miserable, starving, and ravaged by disease death that can happen when an area is overpopulated or subjected to environmental extremes like drought or winter storms.

The conclusion from these two facts? When life gets tough, what you are made of (literally) may contribute to whether or not you survive. Those who survive are the only ones that pass on their genes, the genes that survived.

Those individuals that do survive and reproduce do so because of the characteristics they have, and over time this pattern of inheritance can lead to changes in the characteristics of populations and species. For example, as environments change, characteristics that were once favorable may come to be disadvantageous and the result will be that individuals with different characteristics will reproduce and pass on their characteristics.

The key to evolutionary change is differential reproduction, that is, individuals with certain characteristics will survive and reproduce more often than others having different characteristics. Members of a population of animals or plants that reproduce more than others will pass on their genetic traits more frequently than the rest of the population.

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