12

12.1 The Invention of the Linnaean System

12.2 Species Names

12.3 Higher Categories

12.4 What Is a Species?

12.5 How to Build a Family Tree

12.6 The Kingdoms of Life

12.7 Domain Archaea (Archaebacteria)

12.8 Domain Bacteria (Eubacteria)

12.9 Domain Eukarya (Eukaryotes)

12.10 Viruses: A Special Case

Animations
(Animation Requirements)

• Classification and Phylogeny
• Allopatric Versus Sympatric Speciation
• Molecular Clock
• Significance of Biochemical Differences
• Genetic Data
• Phylogenetic Tree of the Animal Kingdom
• Phylogenetic Tree of Chordates
• Traditional Five-Kingdom System of Classification
• Reproduction of Retrovirus HIV-1

Biodiversity. At its heart, biology is about critters — the great diversity of organisms which share the earth. Research into biodiversity, often carried out in the field, is a rich and rewarding activity. It can also be fun, funny, and intensely interesting.

1. Biodiversity behind bars: Are zoos justified?
2. A fierce argument has broken out among ecologists over biodiversity.
3. Is the number of men in a female's life written in her genes? Polyandry in Galápagos hawks.
4. Violence in Eden: Is Flipper a senseless killer?
5. The killer bees are coming.
6. How did Saint Patrick get the snakes out of Ireland?
7. Going batty: One of the most successful mammals flies at night.

Prions and Mad Cow Disease
Not all diseases are caused by bacteria or viruses. "Mad cow disease" is a fatal and communicable brain disease of cows that is spread by protein molecules from one individual to another. The proteins, called prions, cause brain proteins to fold up incorrectly, eventually leading to brain lesions and death. The prion proteins are very stable, but because cows normally eat grass rather than each other, you would not expect prion infection to be a problem. However, until recent years it was common practice to supplement cattle feed with extra protein, often from the "rendered" bodies of cows that had died in the field. Unfortunately, humans that eat infected cows can acquire the prions too, leading to fatal brain disease for which there is no cure. Some 100 such fatal cases in humans have been reported in Britain, where the outbreak began, but many thousands more are expected. No cases have been reported in the United States, but caution is warranted. Europe was also free of mad cow disease for 15 years after the disease first broke out in England, only to spread to France, Germany, and the rest of Europe in 2000, apparently via contaminated bone meal.

Unearthing the Root of Flowering Plant Phylogeny
The flowering plants have dominated the plant world for over 90 million years, with their ancestors appearing about 135 million years ago. What did this ancestral plant look like? Who are its closest living relatives? The Gnetales, a small group of primitive gymnosperms, share some characteristics with angiosperms, but molecular data seems to rule out the Gnetales as the angiosperm's closest ancestor. Fossils provide a glimpse of the morphological characteristics of early angiosperms, but no clear picture. Ancestral gene sequences in DNA may provide the critical information needed to interpret this early morphological evidence. Plant cells carry DNA in three different compartments: the mitochondrion, the chloroplast, and the nucleus genomes. A complete analysis of plant phylogeny needs to consider phylogenetic estimates based on all three of these genomic compartments. Todd Barkman of Western Michigan University, along with several colleagues, has evaluated available plant genomic data. Their study points to an evolutionary family tree that reveals the root of flowering plant phylogeny.