INTRODUCTION TO EVOLUTION An Overview of Chapters 16 & 17

EVOLUTION  Genetic changes in a species or population over time  Lamarck/Darwin/Wallace  Natural Selection and “Survival of the Fittest”

Vocabulary  Population  Group of individuals from the same species that live in the same area and interbreed  Gene Pool  All the genes and all of their alleles in a population  Evolution (on a population scale)  Any change in the proportions of alleles over time (One allele becomes more common, another becomes less common)  Change in a population NOT change in an individual  Fitness  How well a particular organism can survive and reproduce to pass on its genes to the next generation

 Large-scale, often over a very long time  Branching of one species into two species  All species share a common ancestor Example: Evolution of whales from four-legged land mammals Macro-Evolution

Micro-Evolution  Small-scale  Changes in a population’s gene pool over time  Caused by natural selection and/or genetic drift Example: CF allele becomes more common in European populations because it protects against tuberculosis Micro-evolution leads to Macro-evolution \

How Does Natural Selection Happen? Video: Hummingbirds in Ecuador  What are some adaptations that these hummingbirds have?

Principles of Natural Selection  Genetic variation between individuals Due to mutation and gene shuffling (sexual reproduction)  More offspring are born than can survive  Competition/struggle for limited resources  Some individuals are more genetically “fit” than others – they are better at surviving, reproducing, and passing on their genes Result: Over many generations, the “fit” alleles become more common in the whole population because they are more helpful for surviving and reproducing. SUMMARY: SURVIVAL & REPRODUCTION OF THE FITTEST

Examples of Natural Selection: Ex. 1: Long beaks become more common in a hummingbird population because long beaks help get food Ex. 2: Sickle cell anemia becomes more common in African populations because SCA protects against malaria Ex. 3: CF becomes more common in Europeans because it protects against tuberculosis Ex. 4: Some TB bacteria have evolved to resist antibiotics

SPECIES and SPECIATION Species -  A group of similar organisms  Can breed with each other and produce fertile offspring Examples:  Human species (Homo sapiens)  Horses and donkeys = two separate species because their offspring (mules) aren’t fertile

Speciation -  The formation of new species from a common ancestor  The gene pools of two populations must become separated Ex: The Galapagos Finches

Two Main Steps of Speciation 1. Reproductive Isolation 2. Changes in the Gene Pool Gene Pools Diverge (become different) Genetic Barriers to Reproduction Arise

Reproductive Isolation One population becomes separated and stops breeding with the rest of the species 1. Behavior: Changes in courtship or other reproductive strategies 2. Geographic Geographic barrier splits population (i.e.: river, mountain, body of water, etc.) Populations are separated and cannot interbreed 3. Temporal Species reproduce at different times or have other behavior that becomes time sensitive (i.e.: feeding)

Changes in the Gene Pool A. Gene Pools Diverge (become different): The isolated populations become genetically different. The new environments or behaviors favor different genetic traits (natural selection) B. Genetic Barriers to Reproduction Arise The two populations can no longer interbreed Due to genetic differences in habitat preference, mating behavior, or physical compatibility They are now two separate species!

Hybrid -  The offspring of a mating between two different species  If a hybrid can’t have offspring, there are still two separate species!

Reproductive Barriers That Maintain Separate Species  Before mating occurs  Geographic barriers  Ecological/habitat differences  Temporal differences  Behavioral/courtship differences  Mechanical differences  Chemical differences

Reproductive Barriers That Maintain Separate Species  After mating occurs:  Hybrid dies before birth  Hybrid is weak and sickly  Hybrid is sterile (can’t reproduce)

EVIDENCE FOR EVOLUTION What is the evidence that all species on earth are related to each other and share common ancestors? Overview: 4 Major Types of Evidence: 1. Homologous Structures 2. Embryos 3. Gene Sequences 4. Fossils

1. HOMOLOGOUS STRUCTURES – Similar body parts or bone structures due to sharing a common ancestor that had those structures  Don’t necessarily have the same function now, but did in the common ancestor  Ex: human arm, cat leg, whale flipper, bat wing all have same bones

Homologous Structures, continued: Vestigial Traits -  Don’t have a function now, but suggest that they descended from an ancestor that did use them.  Examples: human tailbone/ostrich wings Ex: human tail bone, human goose animal.nationalgeographic.com

Don’t confuse Homologous Structures with Analogous Structures Analogous Structures - structures that have the same function but NOT the same skeletal structure  This suggests these organisms did NOT descend from a common ancestor with that trait Ex: insect wing and bird wing bio.miami.edu Insect wing Bird wing

2. Embryos Similar characteristics appearing during specific embryonic/ developmental stages of development

3. Gene Sequences Similarities between DNA or amino acid sequences for different organisms  Closer the similarities = Closer relationships

4. FOSSILS Fossils show…  show species that are now extinct  show transitions to new body forms Fossil Artist Rendering

FOSSILS, cont.  Example: Archaeopteryx (lived 150 million years ago)  earliest bird… but has many dinosaur features