Natural SelectionHow have species adapted to their environments over time?

Natural Selection Includes:

1. OVERPRODUCTION: Organisms produce more offspring than their environment can support.

2. HERITABLE VARIATION: Offspring are different in their appearance and function; some of these variations are heritable.

3. COMPETITION: Offspring must compete for survival, food and reproduction.

4. SURVIVAL OF THE FITTEST: Offspring who have the highest fitness for their environment will live longer and/or leave more offspring than those less suited for the environment.

Can we see natural selection in one generation?• No…• This process occurs very slowly, over many

generations• Natural selection can only be observed as

changes in the characteristics or behaviors in populations over time.

Natural Selection…

Caterpillars… what is the benefit of looking like bird poop?

Overproduction & Heritable Variation in butterflies…• How many offspring do butterflies produce?

• 1000+ offspring … not that many survive

• What kind of variation could we see in larva (caterpillars)?• Different color patterns• Different sizes• Diet

• Is this variation in color patterns heritable? • Genes control color patterns in all organisms…

• Offspring from a butterfly (caterpillar) that was green as a larva?• Offspring from a butterfly (caterpillar) that was brown and white as a

larva?

Competition & Survival of the Fittest…• Caterpillars have competition for food, survival &

reproduction.• Who will survive the longest?

• Best camouflage = less likely to be seen by predators = longer survival = more reproduction

• If those that look like bird poop survive longer, what will the population start to look like over many generations?• Like bird poop!

• NATURAL SELECTION – the natural selection of characteristics that allow an animal to blend in with their environments – makes them more fit.

Other examples of selection for survival…

Natural Selection…

Cheetahs… why can they run so fast?

Overproduction & Heritable Variation in cheetahs…• How many offspring do cheetahs produce?

• 5-6 offspring per year … not that many survive

• What kind of variation could we see in cheetahs?• Size of the heart• Length of the legs• Color patterns• + many others

• Is this variation in length of legs heritable? • Genes control color length of limbs in all organisms…

• Offspring from a cheetah with long legs?• Offspring from a cheetah with short legs?

Competition & Survival of the Fittest…• Cheetahs have competition for food, survival & reproduction.• Who will survive the longest?

• Those that can run fast enough to catch prey to survive = longer survival = more reproduction.

• If those that look run faster eat more, what will the population start to look like over many generations?• Fast runners!

• NATURAL SELECTION – the natural selection of characteristics that allow an animal to get more food with their environments – makes them more fit.

Sexual Selection…

The male peacock… why waste so much energy producing feathers?

Overproduction & Heritable Variation in peacocks• How many offspring do they produce?

• 6-8 per year are hatched… not all survive/reproduce

• What kind of variation could we see in male peacocks?• Different color patterns• Different feather sizes• Size of bird

• Is this variation in feather size heritable? • Genes control how large feathers will get…

• Offspring from a peacock with large feathers?• Offspring from a peacock with short feathers?

Competition & Survival of the Fittest…• Peacocks have competition for food, survival & reproduction.• Who will reproduce the most?

• Largest feathers = more reproduction

• If those with large feathers reproduce more, what will the population start to look like over many generations?• Larger feathers, on average.

• SEXUAL SELECTION – the natural selection of secondary sex characterizes in males is WORTH the energy they spend because it increases levels of reproduction – makes them more fit.

Other interesting secondary sex characteristics….

Natural Selection in the last few years…

Antibiotic Resistance

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Methicillin (oxacillin)-resistant Staphylococcus aureus (MRSA) Among ICU Patients, 1995-2004

Source: National Nosocomial Infections Surveillance (NNIS) System

Penicillin resistance in Streptococcus pneumoniae, United

States, 1979–2004

• 1979–1994: CDC Sentinel Surveillance System• 1995–2004: CDC Active Bacterial Core Surveillance

(ABCs) System, Emerging Infections Program

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Vancomycin-resistant EnterocociAmong ICU Patients,

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Source: National Nosocomial Infections Surveillance (NNIS) System

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3rd generation cephalosporin-resistant Klebsiella pneumoniae Among ICU Patients,1995-2004

Source: National Nosocomial Infections Surveillance (NNIS) System

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Fluoroquinolone-resistant Pseudomonas aeruginosa Among ICU Patients,

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Source: National Nosocomial Infections Surveillance (NNIS) System

AZT-Resistant HIV (AIDS virus)

AZT-Resistant HIV (AIDS virus)Resistance to AZT has evolved in all patients taking the drug

(usually in ~6 months)!

How does HIV evolve so rapidly?1. High mutation rate• HIV’s mutation rate is 106 higher than ours!2. Short generation time• 1 year 300 viral generations.≅10 years of viral 2-3 x 10≅ 6 years of human evolution!

Bt-resistant Cotton Bollworm