Evolution by

Natural Selection

Life’s Natural History is a Record of Succession & Extinction

Evolution of life has altered theEarth

In historical context• Darwin did not originate the idea of evolution!!!

1. English naturalist who proposed the theory of evolution by natural selection

Charles Darwin (1809 – 1882)

1. Darwin sailed around the world on the HMS Beagle and carefully studied thousands of different plants and animals

HMS Beagle Voyage 1831-1836

800 km west of mainland

The Galapagos Islands1. Most of animal species on

the Galápagos live nowhere else in world, but they resemble species living on South American mainland.

Unique species

Galapagos Giant Tortiose

Blue-footed Booby

The Birds…1. Galápagos birds

a) 22 of the 29 species of birds on the Galapagos are endemic - found only on these islands

2. One particular group…a) at first, he paid little note

to a series of small but distinctive birds

b) some were woodpecker- like, some warbler-like, & some finch-like

Darwin’s finches1. Darwin was amazed to find out they were all

finchesa) 14 speciesb) but only one species on mainland of

South America - 800 km awayc) all presumably originated from mainland

Correlation of species to food source

Adaptive radiation - divergent evolution in which ancestral species evolve into an array of species to fit a number of diverse habitats.

Darwin’s finches1. Differences in beaks

a) associated with eating different foodsb) adaptations to foods available on islands

2. Darwin’s conclusionsa) when original South American finches

reached islands, adapted to available food in different environments

b) over many generations, the finches changed anatomically & behaviorally

c) accumulation of favorable traits led to the emergence of different species

1. Finches with beak differences allowed them to…a) successfully feedb) successfully competec) successfully

reproduced) pass successful traits

onto their offspring

Darwin’s finches

1. Evolution is the gradual change in a species, or populations over time, not individuals.

2. Darwin was the first scientist to realize that evolution can work by natural selection.

a)Natural Selection – Is a mechanism for change in populations. It occurs when organisms with favorable variations survive, reproduce, and pass their variations to the next generation

i. E.g. Thick fur is a favorable trait in cold environments

Evolution by Natural Selection

Essence of Darwin’s ideas• His theory was simple…

(1)Variation exists in natural populations

(2)Many more offspring are born each season than can possibly survive to maturity

(3) As a result, there is a struggle for existence

(4) Characteristics beneficial in the struggle for existence will tend to become more common in the population, changing the characteristics of a species

(5)Over time, and given a steady input of new variation into a population, these processes lead to the emergence of new species

Natural Selection1. Darwin referred to all of these factors together

as natural selection:a) Variationb) production of more offspring than can survivec) Competition

i. for food, for mates & nesting spots, to escape predators

d) differential survival based on traits

Variation in Populations1. Evolution by natural selection happens in

populations, not individuals. A single organism cannot evolve. Populations evolve.

2. Populations evolve because there is variation

3. Variation causes some organisms to be better fit than others. Better fit organisms are more likely to survive and pass their genes to the next generation

Witness to Evolution• Peppered Moth

◆ dark vs. light variants

Peppered moth

Peppered moth

Year % dark % light1848 5 951895 98 21995 19 81

Peppered moth• Why did the population change?

◆ early 1800s = pre-industrial England

• low pollution• lichen growing on trees = light

colored bark◆ late 1800s = industrial England

• factories = soot coated trees• killed lichen = dark colored bark

◆ mid 1900s = pollution controls• clean air laws• return of lichen = light colored bark

◆ industrial melanism

1. Artificial Selection: Humans choose individuals with certain traits for breeding

2. After many generations of selection, dramatic evolutionary changes can resulti. Dogsii. Fruits/Vegetablesiii. Livestock

Evolution by Artificial Selection

1. Adaptationsa) Structuralb) Mimicryc) Camouflaged) Physiological

2. Fossil Record

3. Comparative Anatomya) Homologousb) Analogousc) Vestigial

4. Embryological Development

5. DNA Similarities

Evidence for Evolution

1. All organisms have adaptations which help them survive in their particular environment

2. Adaptation: a structure or behavior that helps an organism better survive in its environment

Evidence #1 - Adaptations

Evolution of Mole Rats

Adaptations #1 - Structural

Adaptations #2 - Mimicry1. Mimicry: a structural adaptation that

enables one species to resemble another species

a) E.g. A harmless species might mimic a poisonous one

Adaptations #3 - Camouflage1. Camouflage: a structural adaptation

that allows a species to blend in with its surroundings

1. Many bacteria have evolved resistance to antibiotics in the last 50 years

2. Pests have evolved resistance to pesticides

Adaptations #4 - Physiological

Natural selection in action1. Insecticide & drug

resistancea) insecticide didn’t kill

all individualsb) resistant survivors

reproducec) resistance is

inheritedd) insecticide becomes

less & less effective

1. Fossil: Any trace of a dead organism

a) Fossils show the evolution of species over the past millions of years

b) Fossil evidence proves that modern species have evolved from ancient species

Evidence #2 - Fossil Evidence

Archaeopteryx

Puijila the walking seal

Tiktaalik

Evidence #3 - Comparative Anatomy

1. Homologous structures: Body structures on different organisms that are similar in structure (same bones) and DID evolve from a common ancestor

Homologous Structures

Comparative Anatomy2. Analogous structures: Body

structures on different organisms that are similar in function but DID NOT evolve from the same ancestor (bird wing and butterfly wing)

Analogous Wing Structures

Moth (insect)

Pterodactyl (reptile)Bird Bat (mammal)

Comparative Anatomy3. Vestigial structure: body structure

in an organism that no longer serves its original purpose but was useful to an ancestor (useless wings on the African ostrich)

Evidence #4 - Embryological Development1. Early in development, human embryos and

embryos of all other vertebrates are very similar, which suggests that all vertebrates are related

Evidence #5 - DNA Similarities1. Nearly all organisms have DNA, ATP,

and many of the same enzymes2. The DNA (genes) of closely related

organisms looks very similar