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Chapter 22 Descent with Modification: A Darwinian View of Question?

• How did the diversity of life originate? • Through the process of . Evolution

• The processes that have transformed life on earth from its beginnings to today's diversity. • Evolution is the most pervasive principle in biology. Theory vs theory

theory Theory • Layman’s and TV use • Hypothesis supported of the word repeatedly by data • Confused with • Makes testable hypothesis in Science predictions Examples of Theory

• Cell Theory • Big Bang Theory • Atomic Theory • Theory of Gravity • Theory of Evolution Evolution

• Has itself "evolved" or changed over time. • Illustrates “Science as a Process”. • Students should be able to give the main points of several views. Pre-Darwinian Views

1. Greeks 2. Fixed Species 3. Catastophism 4. Hutton and Lyell 5. Lamarck Greek Philosophers

1. - Organisms are already perfectly adapted to their environments. 2. - Organisms arranged on a “scale of life” from simple to complex. Result

• No evolution. • Life is already perfect and doesn’t need to change. • All the rungs on life's "ladder" are already occupied. Fixed Species Concept

• The creator had designed each and every species for a particular purpose. Result

• No evolution. • Created the viewpoint that all species could be identified and named (Taxonomy). • A major factor in the Linnaeus classification system.

• (1769-1832). • Attempted to relate fossils to current life. Theory

• Fossils were the remains of species lost due to catastrophe. • No new species originated; species could only be lost over time. • Result - No evolution.

• 1795 - Gradualism • Profound change is the cumulative product of slow, but continuous processes. Result

• Changes on the earth were gradual, not catastrophic.

Charles Lyell

• 1797 - 1875. • Incorporated Hutton’s gradualism into a theory called Uniformitarianism. Uniformitarianism

• Geological processes have operated at the same rate over the Earth’s history.

Result

• The Earth must be VERY old. (much older than 6000 years of the fixed species concept). • Idea that slow and subtle processes can cause substantial change. Jean Baptiste Lamarck

• Published theory in 1809. • Theory - Life changed from simple to complex over time. Lamarck

• Fossils were the remains of past life forms. • Evolution did occur.

Mechanisms

1. Use and Disuse - – Body parts used to survive become larger and stronger. – Body parts not used to survive deteriorate.

Mechanisms

2. Acquired Characteristics – Modifications acquired by use/disuse were passed on to offspring. Problem

• No of genetics. • Acquired traits are not transmitted to offspring. Lamarck’s Credits

• Did suggest correctly the role of fossils in evolution. • Did suggest that to the environment is a primary product of evolution. Thomas Malthus

• Essay on human population growth in 1798. • Disease, famine, homelessness, and war are inescapable because human populations grow faster than food supplies. • Darwin read Malthus.

• Father of the modern theory of evolution. • Theory - Descent with Modification. Darwin's Background

• Trained as a Naturalist (after trying religion and medicine). Voyage of the Beagle

Result

• Darwin's training and travel opportunities allowed him to formulate and support his ideas on . Galapagos Finches

Alfred Wallace - 1858

• Paper on Natural Selection identical to Darwin's ideas. Result - July 1, 1858

• Dual presentation of the Wallace-Darwin ideas to the Linnaean Society of London.

Darwin - 1859

• Publication of "The Origin of Species” Comment

• Darwin best remembered for the theory because of his overwhelming evidence and because he published. Darwinian View

• is like a tree with branches over time from a common source. • Current diversity of life is caused by the forks from common ancestors.

Example

“The Origin of Species”

• Documented the occurrence of evolution. • Suggested that the mechanism for evolution was Natural Selection. :

Observation 1 – Members of a population often vary greatly in their traits.

. 2

• Traits are inherited from parents to offspring. Observation 3

All species are capable of producing more offspring than their environment can support.

Observation 4

• Owing to lack of food or other resources, many of these offspring do not survive. Inference 1

• Individuals whose inherited traits give them a higher probability of surviving and reproducing in a given environment tend to leave more offspring than other individuals. Inference 2

• This unequal ability of individuals to survive and reproduce will lead to the accumulation of favorable traits in the population over generations.

• Determines which characteristics are favorable. • Determines who survives. • Result - “Natural Selection” Natural Selection in action Artificial Selection

• When man determines the characteristics that survive and reproduce. • Result - the various breeds of animals and plants we’ve developed. Ex. - Mustard Plant

Original Cultivars

Evolution Success Measured By

• Survival • Reproduction • Whoever long enough and has kids is the “winner” in evolution. Requirements

• In order for Natural Selection to work, you must have: – Variations within a population. – Long periods of time (according to Darwin).

Subtleties of Natural Selection

1. Populations are the units of Evolution. 2. Only inherited characteristics can evolve. Comment

• Acquired characteristics may allow a species to evolve "outside" of Natural Selection. • Ex: culture, learning Evidences for Evolution

• Direct observation of evolutionary changes. • Fossils • • Convergent Evolution • • Molecular Direct Observations

• Color patterns in guppies • Drug resistant HIV • Beak size in Birds • Others 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).

HIV Drug Resistance

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

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. Homology

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

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

Evolution Viewpoint

• Remodeling of ancestral structures as their functions or changed. Homology in Embryos

• Problem - closely related organisms go through similar stages in their embryonic development. • Ex: Gill pouches in vertebrates

Convergent Evolution

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

Biogeography

• The geographical distribution of species. • Problem: – Species mixtures on islands – Marsupials in Australia Evolution Viewpoint

• Biogeographical patterns reflect descent from the ancestors that colonized that area.

Molecular Biology

• Study of Evolution at the DNA or protein levels. • Problem - related species have similar DNA sequences.

Evolution Viewpoint

• Related species share a common ancestral DNA. The closer the relationship, the more similar the DNA sequences should be. 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. • Know Darwin’s “observations” and “inferences”. • Be able to discuss the various evidences of Darwinian evolution.