Evolution Darwins Theory of Natural Selection MAIN IDEA

Evolution

Darwin’s Theory of Natural Selection MAIN IDEA: Charles Darwin developed a theory of evolution based on natural selection.

Why was Darwin’s work controversial?

Evolution vs. Creationism – belief that God created all living things to be unique o Evolution – theory that organisms have changed over time. o

Until the 1800 s People thought the same types of organisms on earth were always in existence o This changed when scientists found fossils of organisms no longer on earth o

What made Darwin question previous assumptions on how different organisms came to be?

Scientists observed… Fossil evidence o Many different species o Variations (differences) within species o

Change in Thought Scientists began to wonder how and why these changes took place o 2 biologists believed organisms changed in response to their environments: o n n French Jean Baptiste Lamarck British Charles Darwin

Lamarck’s Theory 1809 – Lamarck proposed his theory of evolution o Theory based on 2 hypotheses: o n n Organisms develop traits by the use and disuse of body parts Acquired characteristics – passed from parents to offspring

According to Lamarck, why do giraffes have long necks?

Lamarck’s giraffe example(Don’t Copy) o o o Lamarck assumed giraffes had short necks originally and ate grass Grass died due to climate change Giraffes ate leaves off trees As giraffes stretched necks, necks grew Giraffe’s acquired long necks – passed to future generations Scientists questioned this theory…

Charles Darwin o o o Born in 1809 Age 22, went on voyage on HMS Beagle (British ship) as a naturalist Mapping expedition of S. America and S. Pacific

Darwin’s Thoughts (Don’t Copy) o o Charles Lyell’s book influenced Darwin Lyell said Earth was millions of years old Observed fossils of marine animals on mountains, etc Observed changing earth: earthquakes, volcanoes, etc; saw change in the land Thought organisms would have to adapt to these changes

Darwin’s Studies Observed thousands of different species o Took careful notes o Collected specimens o Studies fossils o

Galapagos Islands (Don’t Copy) o o o Off coast of Ecuador Observed MANY different species Many similar to those on coast of S. America Observed tortoises, iguanas, finches, etc with slight differences on different islands Ex: different beaks of finches

Help from Gould (Don’t Copy) o o o John Gould, another British naturalist Concluded finches were different species, and were not on mainland of S. America Darwin though species changed after reaching islands

DO NOW What is the difference between natural selection and artificial selection? o What is the difference between natural selection and evolution? o

Artificial vs. Natural Selection o o Artificial - breeding for desired traits Natural – naturally “desired” traits are bred more often – causes gradual change in species over time (evolution)

Darwin’s Theory o o Published book: On the Origin of Species by Means of Natural Selection with help from another scientist, Alfred Russel Wallace Theory based on 4 main ideas: n Variations n Inheritance of traits n Overproduction n Survival of the fittest

Variations (differences) occur among members of the same species o Ex: different breeds of dogs, horses, cats, etc. Inheritance of Variations o Traits are inherited o

Overproduction o o o Organisms produce more organisms than can survive and reproduce This ensures that some offspring will survive to reproduce Ex: fish, insects, frogs, etc.

Survival of the Fittest o o o Organisms with traits that are better for adapting survive to reproduce Pass on these useful traits Natural selection – environment determines which variations will be selected

Peppered Moth Example (DON’T COPY) o o o Early 1800 s, England Peppered moths were mostly light gray; few were white, few were black (variations) Gray blended with tree trunks – birds didn’t see or eat them, so they survived, but black ones were eaten

Peppered Moth Cont’d (DON’T COPY) o o o Industrial Revolution – many factories built Black soot on trees Which moths were NOW more likely to survive?

Do Now o Once, many years ago, horses were the size of cats. Now, they are obviously much bigger. How would Lamarck explain this change? How would Darwin explain it?

Evidence of Evolution o o o Fossils Anatomy Embryos Molecules Biogeography

Fossil Evidence o o Show extinct species Show relationships between current and ancient organisms Show intermediate species – those in between ancient and modern species Difference in traits – derived vs. ancestral

Anatomical Evidence o o o Similar structures found in closely related species; have common ancestor Diverse vertebrates have similar limb structures, but may not have same function –homologous Vestigial structures – structures not currently used by organism; evidence of an organism’s evolutionary past Ex: hind limbs of dolphins/whales

Homologous Structures

Homologous vs. Analogous o o o Remember, homologous – similar STRUCTURE Analogous – structures with similar FUNCTIONS, but different structures/origins Ex: bat’s wing and bird’s wing analogous

Evidence in Embryos o o o Pattern of meiosis (gametes) fertilization mitosis (adults) All vertebrate embryos have homologous structures that may not be in adults: n Tails (most adults keep their tails!) n Limb buds – become limbs Vertebrates have a common ancestor

Molecular Evidence DNA: o Basic genetic code for each species o Ex: humans all have same basic genetic code o Species that are similar have many similarities in their DNA o Species with a more distant ancestor have more differences in DNA

Molecular Evidence Proteins: o Because of similar DNA, organisms of the same species have the same basic proteins o Similar species – similar amino acid sequences in their proteins

Biogeography o o Study of distribution of organisms on earth Similar environments lead to similar adaptations in organisms, even if far apart

Adaptations o o o Traits that allow for survival Fitness – way to measure how effective traits are Examples of adaptations: n n Camouflage Mimicry

Remember that… o o o Not all traits evolve slowly; Ex: bacteria Not all traits increase fitness Mutations can be a source of new traits

Evolution and Genetics

Population o o Members of same species living in same area All genes in a population = gene pool

Population Genetics o Allele frequency – percent of certain alleles (gene types) in a population’s gene pool n o Ex: all homozygous red flowers have a 100% frequency for red alleles Usually remains stable in a population

Changes in the Gene Pool o o o Changes can occur in the gene pool, which could cause evolution Kinds or percentages of genes can change 4 things cause these changes n n Natural selection Mutation Migration isolation

4 Factors Change the Gene Pool 1. Natural selection n n Well-adapted organisms survive to reproduce Pass on genes to next generation, increasing the gene frequency

4 Factors Change the Gene Pool 2. Mutation • • • Adds a new gene to the gene pool Can cause small, immediate change, or go undetected for generations Can be helpful, harmful, or neutral

4 Factors Change the Gene Pool 3. Migration • • Movement of organisms into or out of a population Causes gene flow – movement of genes in or out of populations

4 Factors Change the Gene Pool 4. Isolation n n Organisms become separate from other organisms (geographic isolation) Caused by physical barriers, natural disasters, etc Causes speciation Causes reproductive isolation between the now separate species

Create o With your group, pick any species, and create a scenario as to how it may evolve based on your assigned factor. Base your predictions on facts about the species. Describe and/or draw your predictions, and then present to the class!

The Rate of Evolution

Gradualism o o o Evolution through slow change Believed to be true by Darwin and many other scientists Fossil evidence supports this

Punctuated Equilibrium o o Species remain unchanged for thousands of years, then suddenly undergo rapid changes Fossil evidence of trilobites – unchanged for millions of years, then suddenly died off