LECTURE 2: DARWINIAN EVOLUTION

2 What is Evolution? Evolution is the slow, gradual change in a population of organisms over time

3 What was the Voyage of the Beagle? Charles Darwin Joined Crew of HMS Beagle, 1831 Naturalist 5 Year Voyage around world Collected specimens of South American plants and animals Observed adaptations of plants and animals that inhabited many diverse environments Main focus of geographic distribution of species = Galápagos Islands near the equator west of South America

4 Darwin Left England in 1831 Darwin returned 5 years later in 1836

5 Both Living Organisms & Fossils collectedBoth Living Organisms & Fossils collected Fossils included:Fossils included: TrilobitesTrilobites Giant Ground Sloth of South AmericaGiant Ground Sloth of South America This species NO longer existed. What had happened to them?

Noted flora and fauna on islands off of South America were more like continental species than those of other islands with similar climate and habitatsNoted flora and fauna on islands off of South America were more like continental species than those of other islands with similar climate and habitats Contributions of Lyell and Malthus along with his observations lead him to his mechanism for evolutionContributions of Lyell and Malthus along with his observations lead him to his mechanism for evolution He spent the next 28 years researching more evidence.He spent the next 28 years researching more evidence.

7 What are The Galapagos Islands? Small Group of Volcanic Islands 1000 km West of South AmericaSmall Group of Volcanic Islands 1000 km West of South America Very Different ClimatesVery Different Climates Animals On Islands UniqueAnimals On Islands Unique TortoisesTortoises IguanasIguanas FinchesFinches

9 What are The Galapagos Islands? Island species varied from mainland species & from island-to-island speciesIsland species varied from mainland species & from island-to-island species Each island had long or short neck tortoisesEach island had long or short neck tortoises

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11 What are Characteristics of Finches? Finches on the islands resembled a mainland finchFinches on the islands resembled a mainland finch More types of finches appeared on the islands where the available food was different (seeds, nuts, berries, insects…)More types of finches appeared on the islands where the available food was different (seeds, nuts, berries, insects…) Finches had different types of beaks adapted to their type of food gatheringFinches had different types of beaks adapted to their type of food gathering

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14 What were Darwin’s Observations? Left unchecked, the number of organisms of each species will increase exponentially, generation to generation In nature, populations tend to remain stable in size Environmental resources are limited

15 What were Darwin’s Observations? Individuals of a population vary extensively in their characteristics with no two individuals being exactly alike Much of this variation between individuals is inheritable

16 What were Darwin’s Conclusions? Production of more individuals than can be supported by the environment leads to a struggle for existence among individuals Only a fraction of offspring survive each generation Survival of the Fittest

17 What were Darwin’s Conclusions? Individuals who inherit characteristics most fit for their environment are likely to leave more offspring than less fit individuals Called Natural Selection

18 The unequal ability of individuals to survive and reproduce leads to a gradual change in a population, with favorable characteristics accumulating over generations (natural selection)The unequal ability of individuals to survive and reproduce leads to a gradual change in a population, with favorable characteristics accumulating over generations (natural selection) Eventually, New species evolveEventually, New species evolve What is Darwin’s Theory of Evolution?

19 What are Natural Selection Concepts? The Struggle for ExistenceThe Struggle for Existence –compete for food, mates, space, water, etc. Survival of the FittestSurvival of the Fittest –better adapted able to survive and reproduce Descent with ModificationDescent with Modification –new species arise from common ancestor replacing less fit species

20 What is Fitness? Ability of an Individual To Survive & Reproduce An individual’s contribution of genes to the next generation (i.e. number of offspring) Is Central To The Process Of Evolution –Fitness Is Central To The Process Of Evolution –Individuals With Low Fitness DieDie Produce Few OffspringProduce Few Offspring Survival of the Fittest AKA AKA Natural Selection

21 What are Adaptations? Inherited Characteristic That Increases an Organisms Chance for Survival Adaptations Can Be: –Physical Speed, Camouflage, Claws, Quills, etc.Speed, Camouflage, Claws, Quills, etc. –Behavioral Solitary, Herds, Packs, Activity, etc.Solitary, Herds, Packs, Activity, etc.

22 What is Survival of the Fittest? Key Concept Over Time, Natural Selection Results In Changes In The Inherited Characteristics Of A Population (adaptations). These Changes Increase A Species Fitness In Its Environment

23 Natural Selection Cannot Be Seen DirectlyCannot Be Seen Directly It Can Only Be Observed As Changes In A Population Over Many Successive GenerationsIt Can Only Be Observed As Changes In A Population Over Many Successive Generations –Radiation –Fossil Record

24 What is Common Descent with Modification? Darwin proposed that organisms descended from common ancestorsDarwin proposed that organisms descended from common ancestors Idea that organisms change with time, diverging from a common formIdea that organisms change with time, diverging from a common form Caused evolution of new speciesCaused evolution of new species

25 What is Descent With Modification? Takes Place Over of TimeTakes Place Over Long Periods of Time Species From Their AncestorsSpecies Today Look Different From Their Ancestors –Each Living Species Has Descended With Changes From Other Species Over TimeDescended With Changes From Other Species Over Time

26 Descent With Modification

27 What is Descent With Modification? ImpliesImplies –All Living Organisms Are Related –Single Tree of Life DNA, Body Structures, Energy SourcesDNA, Body Structures, Energy Sources Common Descent –All Species, Living & Extinct, Were Derived From Common Ancestors

#1: Variation is the raw material for natural selection.#1: Variation is the raw material for natural selection. #2 Some Variations are better than others#2 Some Variations are better than others Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig What are the 5 main points of Darwin’s Theory of Evolution by Natural Selection?

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings #3: Living things face a constant struggle for existence. “Survival of the fittest” #3: Living things face a constant struggle for existence. “Survival of the fittest” Organisms produce more offspring than can survive. Organisms produce more offspring than can survive. #4: Only some individuals survive and reproduce. #4: Only some individuals survive and reproduce. Some individuals survive the challenges of life better than others. They have favorable traits Some individuals survive the challenges of life better than others. They have favorable traits

#5: Natural Selection causes genetic change The ones with the favorable trait survive, reproduce and pass on this favorable trait to their offspring.The ones with the favorable trait survive, reproduce and pass on this favorable trait to their offspring. Over time the favorable trait increases in the population.Over time the favorable trait increases in the population.

What are the 5 main points of Darwin’s Theory of Evolution by Natural Selection? Population has variations. Some variations are favorable. More offspring are produced than survive Those that survive have favorable traits. A population will change over time.

Natural Selection and Adaptation Evolutionary biologist Ernst Mayr has dissected the logic of Darwin’s theory into 3 inferences based on five observations

Observation #1 For any species, population sizes would increase exponentially if all individuals that are born reproduced successfully Observation #2 Populations tend to be stable in size, except for seasonal fluctuations Observation #3 Resources are limited Inference #1: Production of more individuals than the environment can support leads to a struggle for existence among individuals of a population, with only a fraction of their offspring surviving

Observation #4 Members of a population vary in their characteristics; no two are exactly alike Observation #5 Much of this variation is heritable Inference #2 Survival depends in part on inherited traits; individuals whose inherited traits give them a high probability of surviving and reproducing are likely to leave more offspring than other individuals

Inference #3 This unequal ability of individuals to survive and reproduce will lead to a gradual change in a population, with favorable characteristics accumulating over generations

A flower mantid in Malaysia A stick mantid in Africa

Species adapt to their environment Natural Selection tends to make a population better suited to its environment.Natural Selection tends to make a population better suited to its environment. The environment determines the direction of genetic change.The environment determines the direction of genetic change. -ADD DIRECTIONAL SELECTION-ADD DIRECTIONAL SELECTION