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Evolution and Diversity of Life

• Theodosius Dobzhansky stated, "Nothing in biology makes sense except in the light of evolution."

History of Evolutionary Thought

• Aristotle believed species were fixed creations arranged by complexity, an idea lasting 2000 years.
• Linnaeus was the first to group similar organisms and assign Latin names.
• The two-word naming system is known as binomial nomenclature

Classification of Animals

• Animals are classified into a hierarchy of groups: Domain, Kingdom, Phylum, Class, Order, Family, Genus, and Species.

Catastrophism

• George Cuvier proposed the idea of catastrophism, based on the study of the fossil in sedimentary rock strata of Paris.
• Cuvier found species that completely disappeared in more recent layers, stating that species disappear due to catastrophic events of the earth's crust like volcanoes and earthquakes

Hutton's Theory of Geological Change

• James Hutton, a Scottish geologist in 1795, studied invertebrate fossils in the Paris Museum.
• Hutton described geological forces that changed Earth over millions of years, such as erosion, earthquakes, and volcanoes.
• Hutton's idea known as gradualism explains changes in the Earth's crust due to slow, continuous processes.

Charles Lyell and Uniformitarianism

• Charles Lyell proposed the theory of uniformitarianism stating that geological processes at uniform rates build and wear down Earth's crust.
• Lyell proposed that the Earth was millions of years old and not thousands of years old.
• Lyell's "Principles of Geology" was published just before the Beagle set sail and was read by Darwin.
• Lyell explained geological processes that shaped the Earth and helped Darwin understand sea shells in the Andes Mountains at 12,000+ feet.

Lamarck's Theory of Evolution

• Jean-Baptiste Lamarck (1809) was one of the first scientists to recognize that change occurs over time.
• Lamarck stated that changes are adaptations to the environment acquired in an organism's lifetime, and these acquired changes were passed to offspring.
• Lamarck's theory is known as the Inheritance of Acquired Characteristics proposed that by selective use or disuse of organs, organisms acquired or lost certain traits during their lifetime. Example:
  • If a body part was used, it got stronger known as Law of Use.
  • If a body part was NOT used, it deteriorated known as Law of Disuse.
  • These traits could then be passed on to their offspring.

Examples of Use and Disuse

• Organisms could change the size or shape of their organs by using them or not using them
• Blacksmiths & Their Sons would have muscular arms
• Giraffe's Necks get Longer from stretching
• Clipped ears of dogs would be passed to offspring as an acquired trait.
• Bird Ancestors Desired To Fly, So They Tried Until Wings Developed.

Lamarck's Mistakes

• Traits are passed through genes, but Lamarck did NOT know how traits were inherited.
• Genes are NOT changed by activities in life
• Change through mutation occurs before an organism is born.

Evolutionary Timeline

Charles Darwin and the Voyage of the Beagle

• Charles Darwin was born on Feb. 12, 1809.
• Darwin joined the crew of HMS Beagle in 1831 as a naturalist.
• Duration of the voyage was 5 years traveling around the world.
• Darwin was an avid collector of flora & fauna, and was astounded by variety of life.
• Darwin left England in 1831 and returned 5 years later in 1836.

The Galapagos Islands

• The Islands are a small group of islands 1000 km West of South America.
• There are very different climates with unique animals like tortoises, iguanas and finches
• The Galapagos Islands are volcanic islands off the coast of South America.
• Island species varied from mainland species & from island-to-island
• Each island had long- or short-neck tortoises and also had different types of beaks adapted to the type of food gathering.

Darwin's Observations & Conclusions

• During the Voyage of the Beagle, Darwin made numerous observations and collected evidence leading to a revolutionary hypothesis about the way life changes over time.
• Darwin observed that the species were not evenly distributed (ex. Australia has Kangaroos but no Rabbits and S. America has Llamas)
• Darwin collected both living organisms and fossils such as trilobites and giant grand sloth of south America leading him to believe that the species no longer exist and made him question what had happened to them
• Evolution is the slow, gradual change in a population of organisms over time.
• Darwin observed that the number of organisms of each species will increase exponentially if left unchecked, while In nature populations tend to remain stable however environmental resources arelimited

Darwin's Conclusion

• 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 causing a survival of the fittest.
• Individuals of a population vary extensively in their characteristics with no two individuals being exactly alike
• Much of this variation between individuals is inheritable. Individuals that inherit characteristics most fit for their environment are likely to leave more offspring than less fit individuals, knowns a Natural Selection

Darwin’s Theory of Evolution

• 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).
• New species evolve.
• Key contributors to Darwin's thinking included Charles Lyell (uniformitarianism), Georges Cuvier (species extinction, catastrophism), Thomas Malthus (struggle for existence, resources), James Hutton (gradualism), John Baptiste Lamarck (inheritance of acquired characteristics, Law of Use and Disuse), and Alfred Russel Wallace (organisms evolved from common ancestors)

Thomas Malthus and Population Growth

• Thomas Malthus, a 1798 economist, observed that babies were being born faster than people were dying.
• Malthus reasoned that resources such as food supply, limit population size.
• Malthus' Influence included High Birth Rates & Limited Resources forcing a Life & Death Competition. Also included the fact that each species struggles for food, living space, and mates

Malthus' Principles

• Malthus reasoned, If The Human Population Continued To Grow Unchecked, Sooner or Later There Would Be Insufficient Living Space & Food For Everyone
• Malthus influenced Darwin stating that plants & animals produce far more offspring than can be supported, leading to the fact that plants and animals have a high death rate and if most of them didn't die world will be overrun
• Death Rate Will Increase To Balance Population size & Food Supply

Common Descent with Modification

• Darwin proposed organisms descended from common ancestors and organisms change with time diverging from a common form Causing Evolution of New Species.

Driving Force for Evolution

• Stongest survive & reproduce during the struggle for resources, which is at least in part b/c The differences between individuals which impact their survival and fertility are inheritable.
• Darwin knew that his theory would be extremely controversial and challenged established religious & scientific beliefs, particularly about the creation of man.
• Darwin refused To Publish Until He Received An Essay From Alfred Wallace, A Fellow Naturalist Who Independently Developed The Same Theory

Wallace's Contribution

• Wallace independently came to the same conclusion as Darwin stating that species changed over time because of their struggle for existence.
• Darwin Presented Wallace's Essay & Some Of His Work At A Scientific Conference of the Linnaean Society in July of 1858 and Then He Started on his book "Origin of Species" and Took It Took Darwin 18 Months To Complete The Book

Natural Variation and Artificial Selection

• Darwin abandoned the idea that species were perfect & unchanging and observed significant variation in all species
• Darwin observed that Farmers Use Variation To Improve Crops & Livestock known as Selective Breeding
• Artificial Selection: Nature Provided The Variation Among Different Organisms, And Humans Selected Those Variations That They Found Useful.

Descent With Modification

• Descent with modification takes Place Over Long Periods of Time and Natural Selection Can Be Observed As Changes In Body Structures, Ecological Niches, orHabitats
• Species Today Look Different From Their Ancestors b/c Each Living Species Has Descended, With Changes, From Other Species ,Over Time
• Implies All Living Organisms Are Related Through a Single Tree of Life »DNA, Body Structures, and Energy Sources by way of Common Descent where All Species, Living & Extinct, Were Derived From Common Ancestors.

Major Problem in Darwin's Theory

• Darwin had no mechanism to explain natural selection and How could favorable variations be transmitted to later generations?
• With the rediscovery of Mendel's work in the first half of the 20th century, the missing link in evolutionary theory was found. The upheaval surrounding evolution began with Darwin's publication of On the Origin of Species By Means of Natural Selection, however , The debate continues nearly 150 years later

Theory of Evolution Today

• Evolution is now found through Homologous Structures, Fossil Record, and Similarities in DNA Sequence.
• Structures That Have Different Mature Forms But Develop From The Same Embryonic Tissues Providing Strong Evidnce of the fact that All Four-Limbed Animals With Backbones Descended, With Modification, From A Common Ancestor are known as Homologous Structures.
• Not All Homologous Structures Serve Important Functions for example Wisdom Teeth are Vestigial Organs
• Earth is Billions of Years Old and Fossils In Different Layers of Rock (sedimentary Rock Strata) Showed Evidence Of Gradual Change Over Time
• Geographic Distribution of Living Species include Different Animals In Different Locations that But Share a Common Ancestor (Ex. Darwin's Finches from South America and spreading to nearby islands and evolving fast and similar Early Development

Key Concepts of The Arguments Darwin made About Evolution.

• Fossil Record
• The Geographical Distribution of Living Species
• Homologous Structures of Living Organisms
• Similarities In Early Development

Darwin's Theory

1. Individual Organisms In Nature Differ From One Another. Some Of This Variation Is Inherited
2. Organisms In Nature Produce More Offspring Than Can Survive, And Many Of These Offspring Do No Reproduce
3. Because More Organisms Are Produced Than Can Survive, Members Of Each Species Must Compete For Limited Resources
4. Because Each Organism Is Unique, Each Has Different Advantages & Disadvantages In The Struggle For Existence
5. Individuals Best Suited To Their Environment Survive & Reproduce Successfully - Passing Their Traits To Their Offspring.
6. Species Change Over Time. Over Long Periods, Natural Selection Causes Changes That May Eventually Lead To New Species
7. Species Alive Today Have Descended With Modifications From Species That Lived In The Past
8. All Organisms On Earth Are United Into A Single Tree Of Life By Common Descent

Factors that Influence Speciation

• Mutation
• Migration
• Natural Selection
• Genetic Drift- Frequency when Alleles show up (due to chance)
• Natural Selection is the process where species adapt to their environment.
• Evolution By Natural Selection Concepts include Variations, The Struggle for Existence, Survival of the Fittest and Descent with Modification.

Natural Selection:

• Results from Variation and the Genetic or Phenotypic, Differences Within A Species and can lead to Survival of the Fittest by way of Adaptations ( Inherited Characteristic That Increases an Organisms Chance for Survival )
• Results from Variation and the Genetic or Phenotypic, Differences Within A Species and can lead to Survival of the Fittest By way of Adaptations ( Inherited Characteristic That Increases an Organisms Chance for Survival -Adaptations Can Be Physical or Behavioral

Key To Survival

• Fitness Is Central To The Process Of Evolution and Individuals With Low Fitness will Die and not Produce Few Offspring therefore Survival of the Fittest aka Natural Selection Leads to Over Time, Natural Selection Results In Changes In The Inherited Characteristics Of A Population and These Changes Increase A Species Fitness In Its Environment
• 4 Types of Natural Selection include Directional, Stabilizing or Disruptive as well as Sexual Selection

Genetic Drift

• Changes to Allele Frequencies due to random chance and can result from The Founder Effect or A Bottleneck Effect.
• Two Evolutionary Time Scales include Microevolution (Short time scale events that change the genotypes and phenotypes of populations) and Macroevolution (Long time scale events that create and destroy species).