EvolutionEvolution

Genetic change in population or Genetic change in population or species over generations.species over generations.

Look at us now!!!Look at us now!!!

• Put some clothes on!

Theories of EvolutionTheories of Evolution

• I. Lamarck’s Explanation:– French scientist (1744-1829)– Proposed that similar species descended

from a common ancestor (fossil records)– He hypothesized that acquired traits were

passed on to offspring.

Acquired TraitAcquired Trait

• It’s not determined by genes!

• Instead, it arises during an organism’s lifetime as a result of the organism’s experience or behavior.– Ex: 1. webbed foot on water birds resulted

from repeated stretching of the membrane between the toes

– 2. tails – if you don’t use it you loose it!

Thomas MalthusThomas Malthus

– Said, “much of human suffering – disease, famine, homelessness and war was the inescapable consequence of the human populations potential to grow much faster than the rate at which supplies of food and other resources could be produced

– Resources couldn’t keep up with the increase in population this kept the population number down.

What were some of DarwinWhat were some of Darwin’’s s observations…observations…

• 1. OVER PRODUCTION OF OFFSPRING all species tend to produce excessive numbers of offspring

• 2. HERITABLE VARIATIONS – individuals of a population vary extensively in their characteristics and that many are inherited

• 3. LIMITED NATURAL RESOURCES – environmental resources are limited

EVOLUTION and NATURAL EVOLUTION and NATURAL SELECTION is NOT the same thing!!SELECTION is NOT the same thing!!

• Evolution = genetic change

• Natural Selection = over production, limited natural resources and heritable variation influence a gradual change in the population!!

Charles Lyell (Scottish Geologist)Charles Lyell (Scottish Geologist)

• Darwin was strongly influenced by his book Principles of Geology

• Gradual forces gradually change Earth’s surface and these forces are still operating today.

• Because of Lyell, Darwin believed that slow natural processes such as growth of mountains due t o earthquakes could account for the presence of marine fossils on the top of mountains!

• Natural catastrophes very important in evolution

Last one!Last one!

• Alfred Wallace:– Had theory IDENTICAL to Darwin!– Caused Darwin to publish “Origin of Species”

by means of natural selection!!!

Beginning of Modern Evolutionary Beginning of Modern Evolutionary TheoryTheory

• II. Charles Darwin (1809-1882) & Alfred Wallace (1823-1913)– “natural selection”-hypothesis that

organisms best suited to their environment reproduced more successfully than other organisms

– Darwin & Wallace announced their hypotheses at the same time

– Darwin’s name became more associated with evolution The Origin of Species published

DarwinDarwin’’s Voyage on the Beagles Voyage on the Beagle

• Sailed in 1831 for five years

• Collected specimens and kept careful records of his observations

• Sailed to South America (Galapagos Islands) and the South Pacific

DarwinDarwin’’s Findingss Findings

• 1. returned to England in October 1836

• 2. collected 13 similar but separate species of finches.

• 3. Each finch species had a distinctive bill for specialized food source.

• Implied that the finches shared a recent common ancestor

DarwinDarwin’’s Finchess Finches

DarwinDarwin’’s Findingss Findings

A GRUB!!!!!!!A GRUB!!!!!!!

• !

DarwinDarwin’’s Theoriess Theories

• TWO THEORIES;– 1. DESCENT WITH MODIFICATION – The

newer forms appearing in the fossil record are actually the modified descendants of older species

• Organisms similar to each other come from a recent common ancestor, organisms that are more dissimilar such as finches and armadillos share a more remote ancestor

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• 2. MODIFICATION BY NATURAL SELECTION – states HOW evolution occurs.– Organisms having traits that make them

better suited for survival tend to leave more offspring than organisms with fewer beneficial traits. Darwin called the different degrees of successful reproduction among organisms in a population NATURAL SELECTION

Evidence to support DarwinEvidence to support Darwin’’s s theory:theory:

• Biogeography – the geographic distribution of species, first suggested to Darwin that organisms evolve from common ancestors

• Comparative Anatomy – the study of the body structures in different organisms, anatomical similarities gives evidence of a common ancestor

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• Homologous structures – structures that are similar in different species of common ancestry but have different functions

• Comparative embryology – closely related organisms often have similar stages in their embryonic development

• Fossils – imprints or remnants of organisms that lived in the past

BiogeographyBiogeography

• Biogeography – is the study of the geographical distribution of fossils and of living organisms.– A comparison of recently formed fossil types

with types of living organisms in the same geographic area shows that new organisms arise in areas where similar forms already lived.

• Ex: armadillos in North & South America where glyptodonts lived in the past.

ArmadillosArmadillos

GlyptodontsGlyptodonts

Evidence of EvolutionEvidence of Evolution

• 1. HOMOLOGOUS STRUCTURES: similar features that originated in a shared ancestor– Similar in structure BUT differ in

function!!– Ex: penguin, bat, alligator, & human (all derive

from the same embryological structures)– These examples i.e. share a fairly recent

common ancestor

Homologous StructuresHomologous Structures

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• 2. ANALOGOUS STRUCTURES: Similar functions BUT differ in structure and embryological development– Ex: wings of a hummingbird and humming

moth – both can hover to feed

Analogous StructuresAnalogous Structures

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• 3. Vestigial Structure: Features that were useful to an ancestor, but they are not useful to the modern organism that has them. – Ex: tailbone in humans, appendix, some

snakes have tiny pelvic bones and limb bones, some whales have pelvic bones along with four chambered stomach like a cow!

Vestigial StructuresVestigial Structures

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• 4. Similarities in Embryology

– Ex: all vertebrate embryos are similar, but those similarities fade as development proceeds – evidence that indicates that vertebrates share a common ancestor

Vertebrate EmbryosVertebrate Embryos

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• 5. Similarities in Macromolecules: The more similar homologous proteins are in different species, the more closely related the species are thought to be.– Ex: the amino acid sequence in human

hemoglobin and gorilla hemoglobin differ by ONE amino acid

– While the Hb of humans and frogs differ by 67 amino acids!!

WhatWhat’’s natural selection?s natural selection?

• A mechanism of evolution that allows for differential (unequal) success in reproduction

• Examples: – Finches – dry years large beaks (stronger)– Finches – wet years small beaks– Insecticides evol. Of hundreds of species

WAIT!!!!!WAIT!!!!!What do you think of this??What do you think of this??

• Oh boy!

LetLet’’s sum it up!s sum it up!

• SURVIVAL OF THE FITTEST!– Those whose characteristics adapt them best

to the environment are most likely to survive and reproduce!!

– Favored traits will be seen more and more while unfavored ones will be seen less and less in ensuing generations

– EVOLUTION IS MEASURED IN A POPULATION NOT IN ONE INDIVIDUAL!

Patterns of EvolutionPatterns of Evolution

• 1. Coevolution: the change of two or more species in close association with each other is called coevolution– Predators and their prey sometimes co-evolve

• Ex: “tropical region” bats feed on nectar– Bats have slender muzzle and long tongue that help

them to feed,flowers are light in color which helps bats to see them at night and have a fruity odor that is attractive to the bats.

Tropical Bats!Tropical Bats!

Baby Bats!!Baby Bats!!

CLOSE UP!!!!CLOSE UP!!!!

• COOL!

Flowers with Nectar!Flowers with Nectar!

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• 2. Convergent Evolution: occurs when the environment selects similar phenotypes, even though the ancestral types were quite different from each other.– Analogous structures, such as similar fins in

very different animals, are associated with convergent evolution

• Ex: sharks and porpoises

PorpoisesPorpoises

SharksSharks

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• 3. Divergent Evolution: two or more related populations or species become more and more dissimilar. Divergence is nearly always a response to differing habitats and can result in new species– A) adaptive radiation: many related species

evolve from a single ancestral species ex: Galapagos finches

– B) artificial selection: all domestic dogs are the same species “Canis familiaris”

DarwinDarwin’’s ideas are supported by s ideas are supported by ARTIFICIAL SELECTIONARTIFICIAL SELECTION

• Artificial Selection – The selective breeding of desired traits that in

fact modify species. Whoa nelly!!!• Ex. Domestic dogs, cats, and plants

– Broccoli, caulif., cabbage, brussel sprouts,

Canis familiarisCanis familiaris

• !

So Darwin reasoned that if..So Darwin reasoned that if..

• So much change could be achieved in a relatively short period of time by artificial selection, then over millions of years and hundreds of thousands of generations, natural selection should be able to modify species considerable.– YEAH BOY, UH-HUH

POPULATION GENETICSPOPULATION GENETICS

• Populations a group of individuals of the same species, living in the same place at the same time

• Populations are the smallest unit that can evolve.

How can we measure evolution?How can we measure evolution?

• As a change in the prevalence of certain traits in a population over several generations

Individuals of a population do NOT Individuals of a population do NOT evolveevolve

• AGAIN…

• Natural selection acts on individuals-their char. Affect their chances of survival and reproduction.

• Evolution is only apparent when a population is tracked over time

Darwin understood evol., but didnDarwin understood evol., but didn’’t t understand the genetic basis of a understand the genetic basis of a

population change…population change…

• Today we know:– Spontaneous mutations may produce new

traits– Segregation & indep. Assort. Produce

variations in gametes & thus in offspring– Genes are passed through gametes from

parents to offspring

MODERN SYNTHESISMODERN SYNTHESIS

• Theory developed in the 1940’s

• Includes genetics and

evolution!!

• POPULATIONS ARE THE UNITS OF EVOLUTION BASED ON NATURAL SELECTION

CONTINUE..CONTINUE..

• Modern synthesis deals with THE RELATIONSHIP BETWEEN POPULATIONS AND SPECIES

• SPECIES=group of organisms that can reproduce fertile offspring!

Where the species live matters!Where the species live matters!

• Species distributed over a geographic range –> have different gene pool

• THAN

• Species localized due to water, islands, mountains etc.!!!

Studying evolution at the Studying evolution at the population level scientist population level scientist focus on the GENE POOLfocus on the GENE POOL

• GENE POOL IS THE SUM OF THE GENES IN A POLULATION!

• (It’s where all members of the next generation get their genes!)

MICROEVOLUTIONMICROEVOLUTION

• When allele frequencies in a population change over generations, this is evolution at its smallest scale.

•(genes are represented by alleles) Ex: gene for the color of your eyes has many alleles – B,b)….

LetLet’’s Review!s Review!

• 1. What is a GENE POOL?

–Sum of genes in a population that will be passed on!!

What is microevolution?What is microevolution?

• when allele frequency in a population change over generations this is evolution at its SMALLEST scale.

Remember!Remember!

• Sexual reproduction on its own does NOT cause microevolution

• Other agents must also act on the population! (environment)

There are several potential There are several potential cause of microevolution:cause of microevolution:

• 1. Genetic Drift:

• - a) bottleneck effect

• - founder effect

• 2. Gene Flow

• 3. Mutation

Genetic DriftGenetic Drift• A change in the gene pool of a small population due to chance!

Genetic DriftGenetic Drift Ex: Northern Elephant Seal (extinct)

The Bottleneck EffectThe Bottleneck Effect

• Genetic drift resulting from an event that drastically reduces population size! Ex: hunting to the point of extinction!

The Bottleneck EffectThe Bottleneck Effect• *

Bottleneck EffectBottleneck Effect• !

The Founder EffectThe Founder Effect•Genetic drift that results from the colonization of a new location by a small number of individuals – small size, less representative of the gene pool.

Founder EffectFounder Effect• Ex: Amish residents of Lancaster County,

PA – Ellis-van Creveld Syndrome

Genetic Drift & Founder EffectGenetic Drift & Founder Effect

• Symptoms: short arms & legs, extra fingers, & in some cases heart defects.

Gene flowGene flow•When fertile individuals move into or out of a population or when gametes are transferred between populations.

Gene FlowGene Flow• *

Gene flowGene flow• *

MutationsMutations•A random change in an organism’s DNA that may create a new allele.

mutationmutation• HUH??

HARDY-WEINBERG HARDY-WEINBERG EQUILIBRIUMEQUILIBRIUM

•Allele frequency with ONLY sexual reproduction involved! •NO OUTSIDE AGENTS

VARIABLESVARIABLES

p = dominantq = recessive2pq = heterozygousp + q = 1p2 + 2pq + q2 = 1

5 Conditions are required for 5 Conditions are required for Hardy-Weinberg EquilibriumHardy-Weinberg Equilibrium

• 1. no mutations

• 2. no migration

• 3. very large population size

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• 4. random mating

• 5. NO NATURAL SELECTION OCCURS!

Hardy-Weinberg EquillibriumHardy-Weinberg Equillibrium

• Conditions rarely met by a natural population

• Gives us a basis to compare nonevolving population vs. actual ones with gene pools that are changing!

Patterns of SelectionPatterns of Selection

• Stabilizing Selection or Balancing Selection

• Disruptive Selection or Diversifying Selection

• Directional Selection

Stabilizing SelectionStabilizing Selection

• Stabilizing selection is a type of natural selection that favors the average individuals in a population. This process selects against the extreme phenotypes and instead favors the majority of the population that is well adapted to the environment. Stabilizing selection is often shown on a graph as a modified bell curve that is narrower and taller than the norm.

Stabilizing CurveStabilizing Curve

Disruptive SelectionDisruptive Selection

• Disruptive selection is a type of natural selection that selects against the average individual in a population. The make up of this type of population would show phenotypes of both extremes, but have very few individuals in the middle. Disruptive selection is the rarest of the three types of natural selection.

Directional SelectionDirectional Selection

• Directional selection is a type of natural selection that favors one extreme phenotype over the mean or other extreme. This phenomena is usually seen in environments that have changed over time. Changes in weather, climate, or food availability lead to directional selection.