Charles Darwin • 1859 – “Origin of Species” published

1. Argued from evidence that species inhabiting Earth today descended from ancestral species *****Descent with modification explains life’s unity and diversity

2. Proposed a mechanism for evolution Natural Selection

In 1844, Darwin wrote an essay on the origin of species and natural selection but did not introduce his theory publicly, anticipating an uproar

In June 1858, Darwin received a manuscript from Alfred Russell Wallace, who had developed a theory of natural selection similar to Darwin’s

Darwin quickly finished The Origin of Species and published it the next year

•Charles Darwin had a consuming interest in nature•First studied medicine (unsuccessfully), and then theology at Cambridge University•After graduating, he took an unpaid position as naturalist and companion to Captain Robert FitzRoy for a 5-year around the world voyage on the Beagle

NORTHAMERICA

EUROPE

AFRICA

AUSTRALIA

GREATBRITAIN

SOUTHAMERICA

ATLANTICOCEAN

PACIFICOCEAN Cape of

Good Hope

Tierra del Fuego

Cape HornTasmania

NewZealand

An

des

Equator

TheGalápagosIslands

Pinta

MarchenaGenovesa

SantiagoDaphneIslands

PinzónFernandina

IsabelaSan

Cristobal

SantaFe

SantaCruz

Florenza Española

•During his travels on the Beagle, Darwin collected specimens of South American plants and animals•He observed adaptations of plants and animals that inhabited many diverse environments

• The most influential stop on the voyage was to the Galápagos Islands

• Darwin noticed that many of the birds and reptiles were unique to specific islands in the Galápagos archipelago

– These included tortoises…

• In the Darwinian view, the history of life is like a tree with branches representing life’s diversity

• Darwin’s theory meshed well with the hierarchy of Linnaeus

https://www.youtube.com/watch?v=Gb_IO-SzLgk

Artificial Selection, Natural Selection, and Adaptation

• Darwin noted that humans have modified other species by selecting and breeding individuals with desired traits, a process called artificial selection

• Darwin then described four observations of nature and from these drew two inferences

https://www.youtube.com/watch?v=bi9Pa0DHG5Y

Fig. 22-9

Kale

Kohlrabi

Brussels sprouts

Leaves

Stem

Wild mustard

Flowersand stems

Broccoli

Cauliflower

Flowerclusters

Cabbage

Terminalbud

Lateralbuds

• Observation #1: Members of a population often vary greatly in their traits

• Observation #2: Traits are inherited from parents to offspring

• Observation #3: All species are capable of producing more offspring than the environment can support

• Observation #4: Owing to lack of food or other resources, many of these offspring do not survive

• Inference #1: Individuals whose inherited traits give them a higher probability of surviving and reproducing in a given environment tend to leave more offspring than other individuals

• Inference #2: This unequal ability of individuals to survive and reproduce will lead to the accumulation of favorable traits in the population over generations

An example of the process of evolution:

• Some populations of head lice won’t be killed by the chemical permethrin, a common treatment

• Studies have shown that this evolution occurred after only about 30 months (40 generations of lice)

The Process of Evolution

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

• Individuals DO NOT evolve

– One louse did not, all of a sudden, have the ability to stay alive when permethrin was in the environment

– The resistance that developed was genetic, passed on from one generation to the next

Fig. 22-12

(b) A stick mantid in Africa

(a) A flower mantid in Malaysia

Direct Observations of Evolutionary Change

• New discoveries continue to fill the gaps identified by Darwin in The Origin of Species

• Examples provide evidence for natural selection:

– Alcohol metabolizing flies

– evolution of drug-resistant HIV

– Antibiotic resistance in bacteria

– Pesticide resistance in insects

Fig. 22-14

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Fig. 22-UN2

• Natural selection does not create new traits, but edits or selects for traits already present in the population

• The local environment determines which traits will be selected for or selected against in any specific population

1. The Fossil Record

• The fossil record provides evidence of the extinction of species, the origin of new groups, and changes within groups over time

(a) Pakicetus (terrestrial)

(b) Rhodocetus (predominantly aquatic)

(c) Dorudon (fully aquatic)

(d) Balaena (recent whale ancestor)

There are 5 major pieces of evidence that supports the theory of evolution

https://www.youtube.com/watch?v=I2C-3PjNGok

Fig. 22-17

Humerus

Radius

Ulna

Carpals

Metacarpals

Phalanges

Human WhaleCat Bat

2. Homologous structures are anatomical resemblances that represent variations on a structural theme present in a common ancestor

Homologous Structures

• 3. Biochemical Evidence

– Molecular level genes shared among organisms inherited from a common ancestor

Fig. 22-18

Human embryoChick embryo (LM)

Pharyngealpouches

Post-analtail

4. Comparative embryology reveals anatomical homologies not visible in adult organisms

5. Vestigial structures are remnants of features that served important functions in the organism’s ancestors

Natural Selection Does Not Result in Perfection

• Natural selection causes populations to be more fit for their environment, not necessarily “better” organisms

• Increased success in one environment does not mean success in a different environment

Poisonous bacteria

Natural Selection Results from Current Environmental Conditions

Changing the population:

• Directional selection – the traits move in a particular direction

– i.e. toward higher metabolism rates; fast metabolizers in fruit flies

– Horse evolution

https://www.youtube.com/watch?v=aTftyFboC_M

Natural Selection Results from Current Environmental Conditions

Stabilize the population:

• Stabilizing selection – extremes are selected against and the traits of the population remain the same because the average condition is the most fit

– i.e. birth weight of human babies (being very small or very large is not as favorable)

Natural Selection Results from Current Environmental Conditions

Splitting the population:

• Diversifying selection – the average condition is the least fit

• Increases the diversity – two or more variants are fit

– i.e. HIV particles – better to evade the immune system

• Differences in individuals arise from differences in their genes

• If DNA is mutated, new alleles may occur

• Natural selection and evolution will occur and the mutation will survive or die out

Biological Species Are Reproductively Isolated

• Alleles do not spread among different species

• Separate species evolve differences, such as lions and leopards

• There is evidence of a common ancestor with spotted coat

– Allele for spots was lost in lions but maintained in leopards

Biological Species Are Reproductively Isolated• Gene pool – all the alleles from all

the individuals in a species

• Gene flow – the spread of an allele through a species’ gene pool

– A change in the frequency of an allele in a gene pool – evolution of that species

• Gene flow does not occur between different species

The Nature of Reproductive Isolated

• If two organisms of different species try to mate, no fertile offspring will be produced

• This is reproductive isolation

• Reproductive barriers to reproduction take two general forms…

– Pre-fertilization

• No attempt to mate

• Or, no fertilized egg is produced – if mating is attempted

– Post-fertilization

• Mating does occur but offspring either do not survive or are sterile

The Nature of Reproductive Isolated

Pre-fertilzation barriers:

• Spatial (habitat) isolation is the most obvious impediment to mating

– The two species never come into contact

• Behavioral isolation is one barrier to species that are close in space

– Differences in mating behaviors

• mating rituals, fireflies blinking, birds songs

The Nature ofReproductive Isolated

• One example of behavioral isolation can be see in the blue-footed boobies

– Male blue-footed boobies have a mating dance to attract females

– Then the female engages in pointing behavior with the male

• If the proper courting display is not present, mating will not occur

http://www.youtube.com/watch?v=lMbDjNDD4cM

http://www.youtube.com/watch?v=T2Bsu4z9Y3k&feature=related

The Nature of Reproductive Isolated

• A barrier to mating resulting from physical incompatibility between sexual organs of two different individuals is called mechanical isolation

• A barrier resulting from the timing of reproduction is a temporal isolation

– Plants produce flowers at different times of year

– Cicadas

– Eastern and western spotted skunks

The Nature ofReproductive Isolated

• Gamete incompatibility is the most common pre-fertilization barrier

– Mating does occur, but the egg and sperm are not compatible

– Fertilization does not occur

The Nature of Reproductive IsolatedPost-fertilization barriers:

• Most interspecies hybrids – offspring of parents from two different species – do not survive long after fertilization

– Incompatibility between genes in different species is the primary cause

• In the case of some species, such as horses and donkeys, the difference in genes is not so large, which is why mules survive and exist sterile

The Process of Speciation

Speciation is the evolution of one or more species from an ancestral form

Three steps are necessary for one species to give rise to another:

1. Isolation of gene pools of populations

2. Evolutionary change in gene pools

3. Evolution of reproductive isolation preventing gene flow

Isolation & Divergence of Gene Pools

• Gene pools may become isolated if a small population migrates to a location far from the main population

Isolation & Divergence of Gene Pools

• The intrusion of a geologic barrier may also isolate gene pools from each other

Isolation and Divergence of Gene Pools

• Allopatric species: isolated populations due to barriers or distance

• Sympatric species: isolated by other means – populations are near one another

The Evolution of Reproductive Isolation

• The exact mechanism of the development of reproductive isolation is still unknown

– When it occurs, the two species follow different evolutionary paths

– The rapidity and course of different forms evolving from a common ancestor is a source of debate between two hypotheses

The Evolution of Reproductive Isolation

• Gradualism – an accumulation of tiny changes over millions of years

• Punctuated equilibrium – no change for millions of years and then drastic changes that are fairly quick (thousands of years)

– The fossil record seems to support the punctuated equilibrium hypothesis

What is a species?

• The biological species concept defines species as a group of individuals that can reproduce with each other, but not other species

• Most commonly used by biologists interested in the process of species formation

• The genealogical species concept defines a species as the smallest group of reproductively compatible organisms containing all of the known descendants of a single common ancestor

– This definition emphasizes evolutionary lineages

– Can be used with asexual organisms

• Genealogical species concept allows easier identification

• If a population is consistently different from other populations, it is a different species, even if it can reproduce with other populations

The Morphological Species Concept

• Paleontologists use the morphological species concept to define a species – a group of individuals that have some reliable physical characteristics distinguishing them from all other species

– They have a similar morphology; look alike in some key feature

• Easy to use in practice on both living and fossil organisms

• Only a few key features needed for identification

• Fossils could represent different ages and genders rather than different species

Convergent Evolution

• Convergent evolution is the evolution of similar, or analogous, features in distantly related groups

• Analogous traits arise when groups independently adapt to similar environments in similar ways

• Convergent evolution does not provide information about ancestry

Flyingsquirrel

Sugarglider

Changes in allele frequencies due to chance is called genetic driftFounder Effect

• Occurs when a small sample of a larger population establishes a new population

• The sample’s gene pool differs from the larger population’s

http://glencoe.mheducation.com/sites/0010122009/student_view0/chapter4/animation_quiz_-_simulation_of_genetic_drift.html

Population Bottleneck

• A dramatic but short-lived population size reduction followed by a rapid increase is called a population bottleneck

• Like the founder effect, it results in the new population differing from the original

Genetic Drift in Small Populations

• Small populations are highly susceptible to changes in allele frequency even by chance

• Humans have a long history of small populations, and thus have been quite vulnerable to genetic drift

Sexual Selection

• Mate preferences exist in many populations

• When a trait influences the likelihood of mating the trait is under the influence of sexual selection, a form of natural selection

– Male peacocks have large showy tails

– Male lions have dramatic manes

• Traits sometimes appear to have not relation to fitness

http://www.youtube.com/watch?v=VuQI8-PsnuM&feature=related