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Chapter 24 The Origin of Species. 1- The fossil record chronicles two patterns of speciation (origin of new species). How would you characterize these.

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Presentation on theme: "Chapter 24 The Origin of Species. 1- The fossil record chronicles two patterns of speciation (origin of new species). How would you characterize these."— Presentation transcript:

1 Chapter 24 The Origin of Species

2 1- The fossil record chronicles two patterns of speciation (origin of new species). How would you characterize these two patterns? Which one would increase species diversity? Why? Fig. 24.1

3 SPECIES C SPECIES ASPECIES B SPECIES D Fig. 24.2

4 2- There are four species in the previous slide. Why is it difficult to define the concept of species based on physical traits? How would you characterize the concept of species? What’s the justification for your answer?

5 Fig Anagenesis (“up” and “origin”) Accumulation in a population of heritable changes, transforming it into a new species. Cladogenesis (“branch” and “origin”) A new species arises from a population that buds from a parent species. Patterns of Speciation Cladogenesis can increase the number of species, anagenesis cannot. page

6 Species (“kind” or “appearance”) Biological species concept: Population or groups of populations whose members have the potential to interbreed with one another in nature to produce viable, fertile offspring, but who cannot produce viable, fertile offspring with members of other species. Largest set in which genetic exchange is possible, at least potentially. Ex: woman in Argentina and man in Bhutan human and cow page 465

7 3- The concept of biological species depends on reproductive isolation; that is, barriers that prevent interbreeding and hence genetic mixing. What do you think are those barriers? How would you classify them?

8 Prezyogtic (“before” and “yoke”) Impede mating or hinder fertilization of ova. Postzyogtic (“after” and “yoke”) Prevent hybrid from developing into a viable, fertile adult. Fig. 24.5

9 To ponder for Thursday Jan 20th Natural hybridization is common and hybrids are not uniformly unfit, they are genotypic classes that are less, equally or more fit than their parental taxa. Some scientists think that hybridization could generate biological diversity. How? Hybridization is common when populations invade new environments. Why? Hybrid

10 1- Impractical for demarcating species, in most cases. For example, interbreeding in many living species fossils. Solution: assign species based on morphological and genetic differences. 2- Useless for completely asexual life forms. For example: bacteria. Solution: assign species based mainly on structural and biochemical traits. Limitations of the biological concept of species page 468 Tursiops aduncusTursiops truncatus

11 In some species, like in these chicks, all individuals are identical I think in all species individuals are identical Actually, in each species individuals differ in some inherited traits. How can you say that? I cannot see any difference among these chicks. Modified from CONCEPT OF SPECIES 4- With whom do you agree? With whom do you disagree? Why?

12 In some species, like in these chicks, all individuals are identical I think in all species individuals are identical Actually, in each species individuals differ in some inherited traits. How can you say that? I cannot see any difference among these chicks. Modified from A) Ignores the fact that there are individual variations that are not immediately obvious to us, such as vocalization in chicks.

13 In some species, like in these chicks, all individuals are identical I think in all species individuals are identical Actually, in each species individuals differ in some inherited traits. How can you say that? I cannot see any difference among these chicks. Modified from B) Ignores the fact that there are individual variations that are immediately obvious to us, such as in humans.

14 In some species, like in these chicks, all individuals are identical I think in all species individuals are identical Actually, in each species individuals differ in some inherited traits. How can you say that? I cannot see any difference among these chicks. Modified from C) Consistent with all available evidence.

15 In some species, like in these chicks, all individuals are identical I think in all species individuals are identical Actually, in each species individuals differ in some inherited traits. How can you say that? I cannot see any difference among these chicks. Modified from D) Ignores the fact that there are individual variations that are not immediately obvious to us, such as vocalization in chicks.


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