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In this chapter, we will address the following questions: What are species? How do new species arise? What happens when newly formed species come together? Why do rates of speciation vary? Why do adaptive radiations occur? | Species and Their Formation 23 Species and Their Formation 23.1 What Are Species? 23.2 How Do New Species Arise? 23.3 What Happens when Newly Formed Species Come Together? 23.4 Why Do Rates of Speciation Vary? 23.5 Why Do Adaptive Radiations Occur? 23.1 What Are Species? Species literally means “kinds.” We recognize most species by their appearance. Many species change little over large geographic ranges. Figure 23.1 Members of the Same Species Look Alike—or Not (A) 23.1 What Are Species? Linnaeus described species based on their appearance—the morphological species concept. Members of species look alike because they share many alleles. He originated the binomial system of nomenclature. 23.1 What Are Species? But males and females may not look alike. Immature individuals may not look like their parents. Other types of information must be used to determine species. Figure 23.1 Members of the Same Species Look Alike—or Not 23.1 What Are Species? Species can be thought of as branches on the tree of life. Speciation: The process by which one species splits into two or more daughter species, often gradually. Figure 23.2 Speciation May Be a Gradual Process 23.1 What Are Species? Speciation involves reproductive isolation—when individuals of a population mate with each other, but not with individuals in another population, they are a distinct evolutionary unit. 23.1 What Are Species? The biological species concept: proposed by Ernst Mayr: “Species are groups of actually or potentially interbreeding natural populations which are reproductively isolated from other such groups.” This does not apply to asexually reproducing organisms. 23.2 How Do New Species Arise? Darwin called speciation the “mystery of mysteries.” Not all evolutionary change results in new species. But if two populations are isolated, over time their genetic structure may change enough so that interbreeding is no longer possible: gene flow must be interrupted. 23.2 How Do New Species Arise? Allopatric . | Species and Their Formation 23 Species and Their Formation 23.1 What Are Species? 23.2 How Do New Species Arise? 23.3 What Happens when Newly Formed Species Come Together? 23.4 Why Do Rates of Speciation Vary? 23.5 Why Do Adaptive Radiations Occur? 23.1 What Are Species? Species literally means “kinds.” We recognize most species by their appearance. Many species change little over large geographic ranges. Figure 23.1 Members of the Same Species Look Alike—or Not (A) 23.1 What Are Species? Linnaeus described species based on their appearance—the morphological species concept. Members of species look alike because they share many alleles. He originated the binomial system of nomenclature. 23.1 What Are Species? But males and females may not look alike. Immature individuals may not look like their parents. Other types of information must be used to determine species. Figure 23.1 Members of the Same Species Look Alike—or Not 23.1 What Are Species? Species can be thought of as branches on
