History of EVOLUTIONARY THEORY & DARWIN & NATURAL SELECTION Ms. Kim Honors Biology

On November 24, 1859, Charles Darwin published On the Origin of Species by Means of Natural Selection. Darwin’s book drew a cohesive picture of life by connecting what had once seemed a bewildering array of unrelated facts. Darwin made two points in The Origin of Species: – Today’s organisms descended from ancestral species. – Natural selection provided a mechanism for evolutionary change in populations. Introduction

What is the difference between Hypothesis and Theory? Hypothesis: Tentative explanation of observations Hypothesis: Tentative explanation of observations Theory: General explanation of important natural phenomena, developed through extensive & reproducible observations & experiments

What is a Scientific Theory? A theory in science is not a “guess” It represents the best model for making sense out of all the evidence. – Germ theory, Electrical theory, Cell theory, etc. Evolution is a well-supported theory drawn from a variety of sources of data: – Observation of the fossil record – Genetic information – Distribution of plants and animals – Similarities across species of anatomy and development

Darwin made two major points in his book called Origins of Species: 1. Many current species are descendants of ancestral species 2. Natural selection is a mechanism for this evolutionary process

Nature and Classification of Species Greek philosopher Aristotle – organisms were perfectly formed and adapted to the world (fixed and unchanging) – Saw adaptations as evidence that a Creator had designed each species for a specific purpose – founder of taxonomy (biology concerned with classifying organisms) & binomial nomenclature (scientifically naming organisms- Species genus) Carolus Linnaeus ( ) “King Philip Came Over For Good Spaghetti”

Fossils, Cuvier, and Catastrophism The study of fossils helped to lay the groundwork for Darwin’s ideas Fossils remains or traces of organisms from the past, usually found in sedimentary rock, which appears in the layers or strata

Western Historical Context French anatomist who largely developed paleontology, the study of fossils Georges Cuvier ( )

Western Historical Context Georges Cuvier ( ) Deeper strata contain older taxa Preferred hypothesis for profound geologic change = catastrophism = Stated that species disappear due to a catastrophic event of the earth’s crust (volcano, earthquake…)

Western Historical Context Scottish geologist who offered an alternative to catastrophism James Hutton ( ) Preferred hypothesis for profound geologic change = gradualism Changes in Earth’s crust due to slow continuous processes (erosion, earthquakes, volcanoes…)

Charles Lyell ( ) Proposed theory of Uniformitarianism Geological processes at uniform rates building & wearing down Earth’s crust Proposed that the Earth was millions of years instead of a few thousand years old

Western Historical Context Jean Baptiste Lamarck ( ) Stated that Changes Are Adaptations To Environment acquired in an organism’s lifetime Said acquired changes were passed to offspring

Lamarck’s Theory of Evolution (1809) Lamarck hypothesized species evolve through use and disuse and inheritance of acquired traits Tendency toward perfection The mechanisms he proposed are unsupported by evidence

Lamarck’s Theory of Evolution Idea called Law of Use and Disuse If a body part were used, it got stronger If body part NOT used, it deteriorated

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inheritance of acquired traits Will his kids be born with big muscles because he has them?

WILL THE OFFSPRING BE NICELY PRUNED?

Tendency toward Perfection Organisms are continually changing and acquiring features that help them live more successfully in their environment. Example: Bird Ancestors Desired to Fly So they tried until wings developed.

Lamarck’s Mistakes Lamarck did NOT know how traits were inherited (traits are passed through genes) Genes are NOT changed by activities in life Change through mutation occurs before an organism is born.

Western Historical Context Thomas Malthus ( ) English demographer Hypothesis: Plants and animals are capable of producing far more offspring than resources can support; the “struggle for existence” (e.g., famine, war) is an inescapable consequence Each Species Struggles For: – Food – Living Space – Mates

Charles Darwin ( ) LOVED nature Sails on HMS Beagle at 22 and voyaged around world Noted flora and fauna on islands off of South America Contributions of Lyell, Hutton and Malthus lead him to his mechanism for evolution species change through natural selection

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

What is a population? A.A group of individuals of the same species inhabiting one area B.All individuals of a species on Earth C.All organisms of all species in an area

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

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

The Galapagos Islands Small group of islands 1000 km west of South America Very different climates Animals on islands unique – Tortoises – Iguanas – Finches

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

What are Characteristics of Galapagos Finches?  Finches on the islands resembled a mainland finch  More types of finches appeared on the islands than the mainland  Finches had different types of beaks

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Darwin’s Focus on Adaptation Adaptation= a change in structure or habits, often hereditary, to improve survival and reproduction in environment – Adaptation to environment and the origin of new species  are closely related processes EXAMPLE – Finches on the islands resembled a mainland finch – Finches had different types of beaks adapted to their type of food gathering

LE 22-6 Cactus eater. The long, sharp beak of the cactus ground finch (Geospiza scandens) helps it tear and eat cactus flowers and pulp. Seed eater. The large ground finch (Geospiza magnirostris) has a large beak adapted for cracking seeds that fall from plants to the ground. Insect eater. The green warbler finch (Certhidea olivacea) used its narrow, pointed beak to grasp insects.

Darwin’s Overall Observations Left unchecked, the # of organisms of each species will increase In nature, populations tend to remain stable in size Environmental resources are limited

More of Darwin’s Observations Individuals of a population vary in characteristics with no 2 individuals being exactly alike. Much of this variation between individuals is inheritable.

Darwin’s Overall Conclusions #1. Variation exists in every population which may have been inherited and the result of a mutation #2. 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

Darwin’s Conclusion #3. Adaptation: Individuals who inherit characteristics (adaptations) that are most fit (suitable/favorable) for their environment are likely to leave more offspring than less fit individuals Called FITNESS High survival = more offspring = more fit #4. Descent with Modification. Over time these adaptations will increase in the population.

What is Common Descent with Modification?  Darwin proposed that organisms descended from common ancestors  Idea that organisms change with time, diverging from a common form  Caused evolution of new species  Takes Place Over Long Periods of Time  Species Today Look Different From Their Ancestors Each Living Species Has ○ Descended With Changes From Other Species Over Time

Darwin’s Descent with Modification descent with modification refers to idea that all organisms are related through descent from common ancestor that lived in the remote past the history of life is like a tree

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) Fitness Is Central To The Process Of Evolution Individuals With Low Fitness ○ Die ○ Produce Few Offspring Survival of the Fittest AKA Natural Selection

Having good “biological fitness” means you are the strongest and biggest. True False

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

Darwin’s Conclusion Natural Selection – gradual, nonrandom process by which traits become more/less common in a population – Acts on PHENOTYPES (adaptations), which influences GENOTYPES – only organisms best adapted to environment tend to survive and transmit genetic traits to future generations while those less adapted tend to be eliminated Key mechanism to evolution

44 Natural Selection  Cannot Be Seen Directly  It Can Only Be Observed As Changes In A Population Over Many Successive Generations Radiation Fossil Record

Video #4: How Does Evolution Really Work?

1844 Darwin wrote an essay on natural selection but did not publish it 1858 Alfred Russell Wallace developed a similar theory of natural selection to Darwin’s (organisms evolve from common ancestors) Darwin quickly finished The Origin of Species and published it the next year

Darwin’s 1 st Idea: Evolution What is evolution? – All accumulated changes across successive generations in inherited characteristics of populations – A change over time in the genetic combination in a population  give rise to diversity Darwins definition = Descent with modification Darwin’s 2 nd Idea: Natural Selection If an environment changes over time, natural selection may result in adaptation to these new conditions  new species can also evolve

What are the 4 conditions of Darwin’s Theory of Evolution by Natural Selection? Population has variations. More offspring are produced than survive Some variations are favorable. Those that survive have favorable traits. A population will change over time.

Use Inheritance of acquired characteristics Generation 1 Generation 2 Natural selection Genetic inheritance from selected population Lamarckism Darwinism