Speciation: Overview

<h1>Text Preview</h1> <p>slide 1</p> <p>Here we are at the Grand Canyon. Standing here at the edge, the canyon seems to go on forever in both directions. The canyon's so deep and wide, we can't even make out people or wildlife at the bottom or on the other side! While the north and south sides are only around 10 kilometers apart, they're very different. The north side is covered by ponderosa pine forests, while the south side is mostly like a desert. Let's split into two groups and see what animals we find on each side.</p> <p>slide 2</p> <p>Look at the squirrels here on the north side. They have black bellies and white tails. The guidebook says they're Kaibab squirrels. Our friends on the south side also found some squirrels. The squirrels there have white bellies and dark tails. The guidebook calls them Abert squirrels.</p> <p>slide 3</p> <p>How did these two closely related, but distinct types of squirrels end up on opposite sides of the Grand Canyon? We'll explore the answers to this and similar questions in this activity. Five million years ago, before the Grand Canyon existed, the common ancestor for the Abert and Kaibab squirrels was found on both sides of the Colorado River. Some of the squirrels could get across the river. All of the gene alleles from the north side squirrels, their gene pool, were constantly mixing with the gene pool on the south side. The transfer of alleles between populations is called gene flow.</p> <p>slide 4</p> <p>Over time, the river cut deeply into the ground, and it became impossible for the squirrels to cross the divide. The gene pool on the north side could no longer mix with the gene pool on the south side. Squirrels mated only with squirrels on their side of the growing canyon. </p> <p>slide 5</p> <p>As the canyon became wider, the conditions on each side became increasingly different. The squirrels on each side adapted in order to survive in their environment. Eventually, the squirrels on the north side became different from the squirrels on the south side. </p> <p>slide 6</p> <p>We've said that Kaibab squirrels are different from Abert squirrels, but what does that really mean? A species is a specific kind of organism, and the origin of a new species through evolution is called speciation. Are Kaibab and Abert squirrels different enough for each to be considered its own species? Has speciation of the squirrels occurred?</p> <p>slide 7</p> <p>In this activity, we'll introduce some barriers that lead to speciation. We'll look at the types of speciation that occur. We'll discuss what can happen when two related species that have been geographically separated, come back into contact and breed with each other. Finally, we'll look at two theories about the rate of speciation. As we learn about speciation, keep in mind that it's the result of evolution. Natural selection drives the changes that lead to new species.</p> <p id="TextCopyright">Copyright 2006 The Regents of the University of California and Monterey Institute for Technology and Education</p>