Individuals don t evolve
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Individuals are selected…. Individuals survive or don’t survive…. Populations evolve!. Individuals DON’T evolve…. Populations Evolve!. Natural selection acts on individuals differential survival “survival of the fittest” differential reproductive success who bears more offspring

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Individuals don t evolve

Individuals are selected…

Individuals survive or don’t survive…


Individuals DON’T evolve…

Populations evolve
Populations Evolve!

  • Natural selection acts on individuals

    • differential survival

      • “survival of the fittest”

    • differential reproductive success

      • who bears more offspring

  • Populations evolve

    • genetic makeup of population changes over time

    • favorable traits (greater fitness) become more common


Changes in populations


Target site

Target site

Resistanttarget site

Insect cellmembrane

Decreased number of target sites

Changes in Populations

Pocket Mice in desert lava flows

Bent Grass on toxic mine site

Insecticide resistance

Evolutionary fitness
Evolutionary Fitness

  • Survival & Reproductive success

    • individuals with one phenotype leave more surviving offspring

Body size & egg laying in water striders

Variation natural s election
Variation & Natural Selection

  • Variation is the raw material for natural selection

    • there have to be differences within population

    • some individuals must be more fit than others

Where does variation come from

Wet year

Beak depth

Dry year

Dry year

Dry year







Beak depth of

offspring (mm)


Medium ground finch






Mean beak depth of parents (mm)

Where does variation come from?

  • Mutation

    • random changes to DNA

      • errors in mitosis & meiosis

      • environmental damage

  • Sex

    • mixing of alleles

      • recombination of alleles

        • new arrangements in every offspring

      • new combinations = new phenotypes

    • spreads variation

      • offspring inherit traits from parent

5 agents of evolutionary change


Gene Flow

Non-random mating

Genetic Drift


5 Agents of Evolutionary Change

1 mutation variation
1. Mutation & Variation

  • Mutation creates variation

    • new mutations are constantly appearing

  • Mutation changes DNA sequence

    • changes amino acid sequence?

    • changes protein?

      • changes structure?

      • changes function?

    • changes in protein may change phenotype & therefore change fitness

2 gene flow
2. Gene Flow

  • Movement of individuals & alleles in & out of populations

    • seed & pollen distribution by wind & insect

    • migration of animals

      • sub-populations may have different allele frequencies

      • causes genetic mixingacross regions

      • reduce differences between populations

Human evolution t oday
Human Evolution Today

  • Gene flow in human populations is increasing today

    • transferring alleles between populations

Are we moving towards a blended world?

EC – 28; October 2010 Scientific American

3 genetic drift



Tree finches

Ground finches

3. Genetic Drift

  • Effect of chance events

    • founder effect

      • small group splinters off & starts a new colony

    • bottleneck

      • some factor (disaster) reduces population to small number & then population recovers & expands again

Founder effect
Founder Effect

  • When a new population is started by only a few individuals

    • some rare alleles may be at high frequency; others may be missing

    • skew the gene pool of new population

      • human populations that started from small group of colonists

      • example:colonization of New World

Journey of Man

Eyes of Nye—Race!

Distribution of human blood types
Distribution of Human Blood Types

  • Distribution of the O type blood allele in native populations of the world reflects original settlement

Distribution of human blood t ypes
Distribution of Human Blood Types

  • Distribution of the B type blood allele in native populations of the world reflects original migration

Out of africa

Journey of Man

Out of Africa

Likely migration paths of humans out of Africa




Many patterns of human traits reflect this migration!

Bottleneck effect
Bottleneck Effect

  • When large population is drastically reduced by a disaster

    • famine, natural disaster, loss of habitat…

    • loss of variation by chance event; NOT SELECTION

      • alleles lost from gene pool

        • not due to fitness

      • narrows the gene pool


  • All cheetahs share a small number of alleles

    • less than 1% diversity

    • as if all cheetahs are identical twins

  • 2 bottlenecks

    • 10,000 years ago

      • Ice Age

    • last 100 years

      • poaching & loss of habitat

Conservation issues

Peregrine Falcon

Conservation Issues

  • Bottlenecking is an important concept in conservation biology of endangered species

    • loss of alleles from gene pool

    • reduces variation

    • reduces adaptability

Breeding programs must consciously outcross

Golden Lion Tamarin

4 non random m ating
4. Non-Random Mating

  • Sexual selection

Sexual selection

Survival doesn’t matterif you don’t reproduce!

Sexual Selection

  • Acting on reproductive success

    • attractiveness to potential mate

    • fertility of gametes

    • successful rearing of offspring

The lion s mane
The lion’s mane…

  • Females are attracted to males with larger, dark manes

  • Correlation with higher testosterone levels

    • better nutrition & health

    • more muscle & aggression

    • longer life

  • But imposes a cost to male

    • HOT! Worth it??

Sexual selection1

Is there a testablehypothesis in there?

Sexual Selection

  • Sexual selection acts in all sexually reproducing species

    • “the traits that get you mates”

    • it influences morphology & behavior

    • it acts on both males and females

Can sexual selection change populations
Can sexual selection change populations?

  • male African long-tailed widowbirds had different amounts of nests based on tail length

  • either artifically or naturally lengthened or shortened


5 natural selection
5. Natural Selection

  • Differential survival & reproduction due to changing environmental conditions

    • climate change

    • food source availability

    • predators, parasites, diseases

    • toxins

  • combinations of allelesthat provide “fitness” increase in the population

    • adaptive evolutionary change

Natural selection
Natural Selection

  • Selection acts on any trait that affects survival or reproduction

    • predation selection

    • physiological selection

    • sexual selection

Predation selection
Predation Selection

  • Acting on predator & prey

    • behaviors & habits

    • camouflage (mimicry)

    • speed

    • defenses (physical & chemical)

Physiological selection

HOT STUFF!Some fish had thevariation of producinganti-freeze proteins

Physiological Selection

  • Acting on body functions

    • fitness (food-gathering)

    • physiology efficiency (oxygen, food, water)

    • disease resistance

    • protection from injury

    • biochemical versatility

5.5 myaThe Antarctic Ocean freezes over

Effects of selection
Effects of Selection

  • Driving changes in a population

5 agents of evolutionary c hange


Gene Flow

Non-random mating

Genetic Drift


5 Agents of Evolutionary Change