Evolution for Beginners Only a theory?

Evolution – science at the core Evolution is not a belief system. It is a scientific concept. It has no role in defining religious beliefs Evolution is a theory…but you don’t get any better than that in science There is a lot of contention about evolution, but not among scientists or scientific organizations.

Basic Definitions Fact: an observation that has been repeatedly confirmed Law: a descriptive generalization about how the physical world behaves Hypothesis: a testable statement that can be used to build inferences and explanations

Basic definitions Theory: a well-substantiated explanation that incorporates facts, laws, inferences and tested hypotheses. Examples? In science, you don’t get any better than a theory.

What is evolution? Let’s start by seeing what evolution is not.

So what does the definition mean? Evolution is a change in the number of times specific genes that code for specific characteristics occur within an interbreeding population Individuals don’t evolve, populations do

A brief history of evolution Charles Darwin was born on February 12, 1809 in Shrewsbury, England. From 1831 to 1836 Darwin served as naturalist aboard the H.M.S. Beagle on a British science expedition around the world. He observed much variation in related or similar species of plants and animals that were geographically isolated from each other. These observations were the basis for his ideas.

A brief history of evolution Contrary to popular belief, Darwin was not the first person to describe the concept of evolution, but he was the one who gave it its driving force.

The Other Scientists Jigsaw

Natural Selection Darwin knew nothing of genes, but what he did have were two observations and a little inference that provided the motive force for evolution.

Scientific Method Review What is the first step of the scientific Method? Make Observations! What is an inference? Using prior knowledge, known facts, evidence and experience to draw a conclusion

Natural Selection Observation 1: Organisms generally have more offspring than can survive to adulthood. Observation 2: Offspring are not identical. There is variation in their appearance, size, and other characteristics.

Natural Selection Inference: Those organisms that are better adapted to their environment have a greater likelihood of surviving to adulthood and passing these characteristics on to their offspring. Survival of the “fittest.”

Darwinian Evolution Before publishing The Origin of Species, Darwin received a letter from a colleague. Alfred Russell Wallace, exploring in Asia, had come to the same conclusion as Darwin. In Darwin’s lifetime he would be recognized as one of the great masters of science. By the 1870s almost all serious scientists in England had accepted evolution.

Review of Genetics Cells are the basic unit of life Cells have DNA DNA contains genes Genes code for proteins, usually enzymes Genes that differ slightly are called alleles Different alleles make different forms of the same enzyme These enzymes determine an organisms phenotype Alleles can be inherited

EVOLUTION & SPECIATION

VOCABULARY REVIEW EVOLUTION – CHANGE OVER TIME NATURAL SELECTION - INDIVIDUALS BETTER ADAPTED TO THE ENVIRONMENT ARE ABLE TO SURVIVE & REPRODUCE. A.K.A. “SURVIVAL OF THE FITTEST”

POPULATION – GROUP OF INDIVIDUALS OF SAME SPECIES THAT INTERBREED GENE POOL – COMMON GROUP OF ALL GENES PRESENT IN A POPULATION

Gene Pool Combined genetic info. of all members Allele frequency is # of times alleles occur

How does Evolution Occur? Mutation No gene flow Small population size Non-random mating Natural selection Disruptive Directional Stabilizing

Do we see variation within different wild species ? Natural Selection: It is the production of variations due to: Mutations: Changes in the DNA Meiosis: crossing over during Prophase I Random mate selection & fertilization

Variations With in a Family:

Variation in Populations 2 processes can lead to this: A. Mutations - change in DNA sequence B. Gene Shuffling– from sexual reproduction

Genetic Drift changes populations……. Random change in allele frequency causes an allele to become common

Founder Effect: a cause of genetic drift attributable to colonization by a limited number of individuals from a parent population

phenotypes of original population phenotype of island population A seabird carries a few seeds, stuck to its feathers, from the mainland to a remote oceanic island. Founder Effect

Bottleneck Effect: Elephant seal Año Nuevo State Park Reduction of a population’s gene pool produced when a few members survive the widespread elimination of a species.

Bottleneck Effect

Gene Flow: genetic exchange due to the migration of fertile individuals or gametes between populations (reduces differences between populations)

Natural Selection: differential success in reproduction; only form of microevolution that adapts a population to its environment

Sexual selection Sexual dimorphism: secondary sex characteristic distinction Sexual selection: selection towards secondary sex characteristics that leads to sexual dimorphism

Single-Gene vs. Polygenic Traits Single-Gene: 2 Distinct Phenotypes Polygenic: Many Phenotypes (EG: tongue rolling)

Natural Selection on Polygenic Traits Shifts to middle range Shifts to 2 extremes Shifts to 1 extreme

Main Types of Selection Pressures Directional Selection Natural selection favors one extreme of the population for that trait often happens when environment changes in a consistent way- e.g.climate gets colder. Disruptive Selection Natural selection favors both extremes selected Causes species to diverge Stabilizing Selection Natural selection favors the average for population selected

Original Population

Directional Selection Neck of Giraffe Antibiotic resistance of bacteria Moth color (melanin) Camouflage/Mimicry

Directional Selection: Mimicry (mimic environment)

Stabilizing Selection When the extremes of the trait aren’t as well suited Examples bird clutch size Human birth weight Human height

Disruptive Selection Causes divergence within the species Occurs when two different types of resources in one area Results in specialization for each branched group May lead to formation of new species E.g. Darwin’s Finches

What acts as a selection pressure on a population? Competition for food Competition for a mate Changes in the environment Predators Parasites

Examples of selection pressures... Predators - variants with adaptations allowing them to escape predators have more offspring - e.g. speed, defensive weapons, camouflage, mimicry Prey/Food - variants with adaptations allowing them to obtain food have more offspring - e.g. Speed, senses for finding prey/food, weapons for killing prey or obtaining food, camouflage for stealth Climate - those who can survive new climate best have more kids - e.g. ice age, change in climate due to migration. Mates - variants with adaptations allowing them to attract a mate to have offspring - e.g. strong, attractive, good provider

Original Population Mechanisms of Evolution: Natural Selection

After Chemical Spill Mechanisms of Evolution: Natural Selection

Many Generations Later Mechanisms of Evolution: Natural Selection

Mechanism of Evolution: Mutations Original Population

Mechanism of Evolution: Mutations After Mutation

Mechanism of Evolution: Mutations Many Generations Later

 R eal-World Examples: 01/IIIC2aCasestudy.shtml Mechanisms of Evolution: Mutations

Mechanism of Evolution: Gene Flow Original Population Neighboring Population

Mechanism of Evolution: Gene Flow After Migration

Mechanism of Evolution: Gene Flow Many Generations Later

 Real-World Examples: C4aGeneflowdetails.shtml Mechanisms of Evolution: Gene Flow

Original Population Mechanisms of Evolution: Genetic Drift

After Lightning Mechanisms of Evolution: Genetic Drift

Many Generations Later Mechanisms of Evolution: Genetic Drift

 Real-World Examples: home/harvey/lect/lectures.html?flnm=nsln&ttl= Population%20change%20and%20natural%20s election&ccode=el&mda=scrn hill.com/sites/dl/free/ /126997/anim ation45.html Mechanisms of Evolution: Genetic Drift

Original Population Mechanisms of Evolution: Artificial Selection

Many Generations Later Mechanisms of Evolution: Artificial Selection

 Real-World Examples: iation/artificial/ Mechanisms of Evolution: Artificial Selection

What is a Species?  A group of individuals that actually or potentially interbreed in nature. A species is the biggest gene pool possible under natural conditions.  Scientists group organisms according to their similarities.  The most similar organisms belong to a species.  Members of the same species can mate and produce fertile offspring. Ex: Humans belong to the species Homo sapiens.

SPECIATION THE FORMATION OF NEW SPECIES AS NEW SPECIES EVOLVE, POPULATIONS BECOME REPRODUCTIVELY ISOLATED REPRODUCTIVE ISOLATION – MEMBERS OF 2 POPULATIONS CANNOT INTERBREED & PRODUCE FERTILE OFFSPRING.

3 ISOLATING MECHANISMS…….. BEHAVIORAL ISOLATION- CAPABLE OF BREEDING BUT HAVE DIFFERENCES IN COURTSHIP RITUALS (EX. MEADOWLARKS) GEOGRAPHICAL ISOLATION – SEPARATED BY GEOGRAPHIC BARRIERS LIKE RIVERS, MOUNTAINS, OR BODIES OF WATER (EX. SQUIRREL) TEMPORAL ISOLATION – 2 OR MORE SPECIES REPRODUCE AT DIFFERENT TIMES.

Table 23.1a

Tigon Result of male tiger and female lion mating incaptivity. Offspring are infertile. Separated both geographically and ecologically.

Table 23.1b

Fig Four species of leopard frogs: differ in their mating calls. Hybrids are inviable.

These squirrels live on opposite sides of the Grand Canyon. This is an example of allopatric speciation.

SPECIATION IN DARWIN’S FINCHES SPECIAITON IN THE GALAPAGOS FINCHES OCCURRED BY: - FOUNDING OF A NEW POPULATION, - GEOGRAPHIC ISOLATION which led to - - REPRODUCTIVE ISOLATION and CHANGES IN THE NEW POPULATION’S GENE POOL due to COMPETITION.

Evidence of Evolution 1. Fossil Record 2. Geographic Distribution of Living Species 3. Homologous Body structures 4. Similarities in Embryology

Evidence of Evolution Fossil Record provides evidence that living things have evolved Fossils show the history of life on earth and how different groups of organisms have changed over time

Rat like common ancestor Mammalia Placental mammals Marsupial Mammals Sugar Glider Flying Squirrel Convergent Evolution and Analogous Structures

Big Question!!!  How did life arise on the big blue planet??  Scientists attempt to answer this question scientifically.

Relative Dating versus Absolute Dating

Relative Dating Can determine a fossil’s relative age Performed by estimating fossil age compared with that of other fossils Drawbacks – provides no info about age in years

Absolute dating Can determine the absolute age in numbers Is performed by radioactive dating – based on the amount of remaining radioactive isotopes remain Drawbacks - part of the fossil is destroyed during the test

Carbon-14 Dating

Fossil Formation

 A cosmic explosion that hurled matter and in all directions created the universe billion years ago  Evidence  it explains why distant galaxies are traveling away from us at great speeds  Cosmic radiation from the explosion can be observed  The Big Bang theory probably will never be proven; consequentially, leaving a number of tough, unanswered questions. Big Bang Theory

What was early earth like?  Earth was Hot!!  Little or no oxygen  Gasses in atmosphere:  Hydrogen cyanide (poison to you!)  Hydrogen sulfide  Carbon dioxide  Carbon monoxide  Nitrogen  water

So how did the earth get oxygen?  Some of that oxygen was generated by photosynthetic cyanobacteria  Some came from the chemical separation of water molecules into oxygen and hydrogen.

 Oxygen drove some life forms to extinction  Others evolved ways of using oxygen for respiration

How did life begin? Miller and Urey’s Experiment  Passed sparks through a mixture of hydrogen methane ammonia and water  This produced amino acids – the building blocks of life

Miller’s experiment suggests that lightning could have produced amino acids

How can simple amino acids result in life? There are 3 theories 1. Formation of microspheres  Large organic molecules can sometimes form tiny proteinoid microspheres  Store and release energy, selectively permeable membranes, may have acquired more characteristics of living cells

2 nd Hypothesis for Life Evolution of RNA to DNA RNA was assembled from simple organic molecules in a primordial soup RNA was assembled from simple organic molecules in a primordial soup RNA was able to replicate itself and eventually form DNA RNA was able to replicate itself and eventually form DNA Not scientifically proven to be possible Not scientifically proven to be possible

3 rd Theory of Life Endosymbiotic theory  eukaryotic cells arose from living communities formed by prokaryotic organisms  Ancient prokaryotes entered primitive eukaryotic cells and remained there as organelles