Chapter 22 Part 3 Descent with Modification A Darwinian View of Life

Concept 22.3: Evolution is supported by an overwhelming amount of scientific evidence New discoveries continue to fill the gaps identified by Darwin in The Origin of Species Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Direct Observations of Evolutionary Change Two examples provide evidence for natural selection: the effect of differential predation on guppy populations and the evolution of drug-resistant HIV Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Direct Observations Color patterns in guppies Drug resistant HIV Beak size in Birds Others

Predation and Coloration in Guppies : Scientific Inquiry John Endler has studied the effects of predators on wild guppy populations Brightly colored males are more attractive to females However, brightly colored males are more vulnerable to predation Guppy populations in pools with fewer predators had more brightly colored males Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Color Pattern in Guppies Field Experiment (see text for full details) Changed the selection pressure on male guppies Result – color pattern change in 15 generations (22 months).

As predicted, over time the population became less brightly colored Endler transferred brightly colored guppies (with few predators) to a pool with many predators As predicted, over time the population became less brightly colored Endler also transferred drab colored guppies (with many predators) to a pool with few predators As predicted, over time the population became more brightly colored Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

HIV Drug Resistance Drug resistance strains selected for by treatments Result – resistant strains became 100% dominant in 4-5 weeks.

The Evolution of Drug-Resistant HIV The use of drugs to combat HIV selects for viruses resistant to these drugs HIV uses the enzyme reverse transcriptase to make a DNA version of its own RNA genome The drug 3TC is designed to interfere and cause errors in the manufacture of DNA from the virus Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

The Evolution of Drug-Resistant HIV The use of drugs to combat HIV selects for viruses resistant to these drugs HIV uses the enzyme reverse transcriptase to make a DNA version of its own RNA genome The drug 3TC is designed to interfere and cause errors in the manufacture of DNA from the virus Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Some individual HIV viruses have a variation that allows them to produce DNA without errors These viruses have a greater reproductive success and increase in number relative to the susceptible viruses The population of HIV viruses has therefore developed resistance to 3TC The ability of bacteria and viruses to evolve rapidly poses a challenge to our society Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Beak Size Field Study – measured the beak size of all birds in a population over several years. Result – drought and food competition changed beak size.

Fossils Relics or impressions of organisms from the past. Problem: Show changes over time from simple to complex. Many fossils don't have descendants.

Evolution Viewpoint Life has changed over time. Many species failed to survive and became extinct.

Comments 1. Fossilization is a rare event. 2. Only hard parts fossilize well. 3. Problem in finding fossils. 4. Interpretation. 5. Missing Links.

Natural selection does not create new traits, but edits or selects for traits already present in the population The local environment determines which traits will be selected for or selected against in any specific population Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

The Fossil Record The fossil record provides evidence of the extinction of species, the origin of new groups, and changes within groups over time Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

The Fossil Record The fossil record provides evidence of the extinction of species, the origin of new groups, and changes within groups over time Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 22-15 2 4 4 6 4 Bristolia insolens 8 3 Bristolia bristolensis 10 2 4 4 6 4 Bristolia insolens 8 3 Bristolia bristolensis 10 12 3 Depth (meters) 2 Bristolia harringtoni 14 16 18 1 Bristolia mohavensis 3 Figure 22.15 Fossil evidence of evolution in a group of trilobites 2 1 Latham Shale dig site, San Bernardino County, California

The Darwinian view of life predicts that evolutionary transitions should leave signs in the fossil record Paleontologists have discovered fossils of many such transitional forms Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 22-16 (a) Pakicetus (terrestrial) (b) Rhodocetus (predominantly aquatic) Figure 22.16 The transition to life in the sea Pelvis and hind limb (c) Dorudon (fully aquatic) Pelvis and hind limb (d) Balaena (recent whale ancestor)

Homology Homology is similarity resulting from common ancestry Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Homology Mammal forelimbs Homologous Structures - Common "building plan” with divergent functions.

Humerus Radius Ulna Carpals Metacarpals Phalanges Human Cat Whale Bat Fig. 22-17 Humerus Radius Ulna Carpals Metacarpals Figure 22.17 Mammalian forelimbs: homologous structures Phalanges Human Cat Whale Bat

Anatomical and Molecular Homologies Homologous structures are anatomical resemblances that represent variations on a structural theme present in a common ancestor Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Vestigial Organs Whale Legs Rudimentary structures of marginal, if any, use.

Human Example

Human Example

Evolution Viewpoint Remodeling of ancestral structures as their functions or adaptations changed.

Homology in Embryos Closely related organisms go through similar stages in their embryonic development. Ex: Gill pouches in vertebrates

Comparative embryology reveals anatomical homologies not visible in adult organisms Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Vestigial structures are remnants of features that served important functions in the organism’s ancestors Examples of homologies at the molecular level are genes shared among organisms inherited from a common ancestor Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Homologies and “Tree Thinking” The Darwinian concept of an evolutionary tree of life can explain homologies Evolutionary trees are hypotheses about the relationships among different groups Evolutionary trees can be made using different types of data, for example, anatomical and DNA sequence data Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Convergent Evolution Convergent evolution is the evolution of similar, or analogous, features in distantly related groups Analogous traits arise when groups independently adapt to similar environments in similar ways Convergent evolution does not provide information about ancestry Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Convergent Evolution Unrelated organisms show similar adaptations. Cause – lived in a similar environment with similar selection pressures.

Biogeography Darwin’s observations of biogeography, the geographic distribution of species, formed an important part of his theory of evolution Islands have many endemic species that are often closely related to species on the nearest mainland or island Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Earth’s continents were formerly united in a single large continent called Pangaea, but have since separated by continental drift An understanding of continent movement and modern distribution of species allows us to predict when and where different groups evolved Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Evolution Viewpoint Biogeographical patterns reflect descent from the ancestors that colonized that area.

Molecular Biology Study of Evolution at the DNA or protein levels. Related species have similar DNA sequences.

Evolution Viewpoint Related species share a common ancestrial DNA. The closer the relationship, the more similar the DNA sequences should be.

What Is Theoretical About Darwin’s View of Life? In science, a theory accounts for many observations and data and attempts to explain and integrate a great variety of phenomena Darwin’s theory of evolution by natural selection integrates diverse areas of biological study and stimulates many new research questions Ongoing research adds to our understanding of evolution Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Individuals in a population vary in their heritable characteristics. Fig. 22-UN1 Observations Individuals in a population vary in their heritable characteristics. Organisms produce more offspring than the environment can support. Inferences Individuals that are well suited to their environment tend to leave more offspring than other individuals and Over time, favorable traits accumulate in the population.

Fig. 22-UN2

Fig. 22-UN3

You should now be able to: Describe the contributions to evolutionary theory made by Linnaeus, Cuvier, Lyell, Lamarck, Malthus, and Wallace Describe Lamarck’s theories, and explain why they have been rejected Explain what Darwin meant by “descent with modification” List and explain Darwin’s four observations and two inferences Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Explain why an individual organism cannot evolve Describe at least four lines of evidence for evolution by natural selection Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Summary Darwin's ideas now a "Theory”. Predictions of a Theory are tested by experiments and observations. Be familiar with the pre-Darwin views of evolution.

Summary Know Darwin’s “observations” and “inferences”. Be able to discuss the various evidences of Darwinian evolution.