What is Evolution? Study of how things change over … is Evolution? • Study of how things change...

10.2 Darwin’s Observations

What is Evolution?• Study of how things change over time

15 Darwin’s Theory of Evolution


Theories of Evolution - Lamarck

• Jean Baptiste Lamarck (1744 – 1829)► Law of Use and Disuse

- parts of the body that are used become more developed

- unused body parts become smaller and eventually disappear

► Law of Inheritance of Acquired Characteristics - organisms can pass traits acquired during their lifetime to their offspring

- ex. giraffe evolution


10.2 Darwin’s ObservationsTheories of Evolution - Lamarck• Lamarck’s explanation of how giraffes evolved long

neck:1) In order to reach higher leaves,

giraffes stretch their necks andacquire long necks. (Law of Useand Disuse)

2) They can pass their acquired long neck trait to their offspring.(Law of Inheritance of AcquiredCharacteristics)

3) Eventually, all giraffes have longnecks over time.

• Lamarck’s explanation was believed to be invalid.



Theories of Evolution - Darwin

• Charles Darwin (1809-1882)- traveled on HMS Beagle to Galapagos

Islands observing and collecting samples of organisms



Warbler finch

Woodpecker finchSmall

insectivoroustree finch

Largeinsectivorous

tree finch

Vegetariantree finch

Cactus finchSharp-beaked finch

Small groundfinch

Mediumground finch

Large groundfinch

Insect eaters

Bud eater

Seed eaters

Cactuseater

Theories of Evolution - Darwin• Darwin observed that:

1) the Galápagos Islands were close together but had very different climates.

2) the characteristics of many animals and plants varied noticeably among the different islands of the Galápagos. (ex: 14 species of finches)


10.2 Darwin’s ObservationsTheories of Evolution - Darwin• Darwin wondered if finches living on different islands

had once been members of the same species. • These separate species would have evolved from an

original South American ancestor species.




• Darwin’s conclusions: – variations in beaks

► differences in beaks in the original flock► adaptations to foods available on islands

– natural selection for most fit► over many generations, the finches were

selected for specific beaks & behaviors– offspring inherit successful traits

► accumulation of winning traits: both beaks & behaviors

– separate into different species




• Darwin collected the preserved remains of ancientorganisms, called fossils.

• Some of those fossils resembled organisms that werestill alive. Others looked completely unlike anycreature he had ever seen.

present day Armadillosancient Armadillo




• Darwin published the book“The Origin of Species” in 1859(32 years after the end of his voyage).

• Darwin proposed the Theory ofEvolution by Natural Selection:individuals with traits best suited for a specific environmentsurvived and passed on these traits to their offspring.

15 Darwin’s Theory of Evolution15 Darwin’s Theory of Evolution

10.2 Darwin’s ObservationsTheories of Evolution - Darwin• How would Darwin have explained the evolution of

giraffe’s long neck differently than Lamarck?• Based on Darwin’s theory of

natural selection:1) Long neck giraffes were better

suited for reaching higher leaves and survived better.

2) More long neck giraffes survivedover time and passed on the long neck traits to their offspring.

3) Short neck giraffes died out because they could not competewith the long neck giraffes.



Several key insights led to Darwin’s idea for natural selection. • Darwin noticed domesticated plants and animals

seemed to show traits that were not found in their wild relatives.

• Breeders of these domesticated plants and animals select the desired traits (instead of the environment).

neck feathers

crop

tail feathers



Several key insights led to Darwin’s idea for natural selection. • Artificial selection is the process by which humans

select traits through breeding. (aka “selective breeding”)



Several key insights led to Darwin’s idea for natural selection. • Darwin compared processes in nature to artificial

selection. • In artificial selection, human selects the desired

traits; while in natural selection, environment (or nature) selects the desired traits.

• In nature, there is always struggle for survival because of limited resources of food, water, and shelter.



• There are four main principles to the theory of natural selection.

Natural selection explains how evolution can occur.

1) Overproduction:

OVERPRODUCTION

A jaguar may produce more offspring than they can survive due to struggle for survival.



2) Variation: heritable differences among individuals.Natural selection explains how evolution can occur.

VARIATION

Jaguar 1 Jaguar 2

Jaguar 1 = larger jaws and teethJaguar 2 = smaller jaws and teeth



3) Adaptation: a feature that allows an organism to better survive in its environment


ADAPTATION

Jaguars with larger jaws and teeth have better adaptations for eating shelled reptiles, so they are more likely to survive and reproduce better.(survival of the fittest)



4) Descent with Modification:Over time, natural selection will produce more individuals with the adaptations that are better suited for a particular environment.


DESCENT withMODIFICATION

Larger jaws and teeth become the more common traitsin the population. So jaguars’ descendants showedmodification, or change, over time.



Modern Day Example of Natural Selection

• Industrial Melanism of peppered moths- Industrial Revolution in Europe during 1850s affected the natural selection on colors of the peppered moths

- As the environment changed, the moths that couldcamouflage themselves had better chancesof survival and reproduction.

Year % dark % light1848 5 951895 98 21995 19 81



Modern Day Example of Natural Selection– early 1800s = pre-industrial England

►low pollution► lichen on trees = light colored bark► light colored moths survived better

– late 1800s = industrial► factories = soot coated trees► killed lichen = dark colored bark► dark colored moths survived better

– mid 1900s = pollution controls► clean air laws► return of lichen = light colored bark► light colored moths survived better again



Natural selection acts on distributions of traits.

• A normal distribution, represented by a bell-shaped curve, is generally found in a typical population.

• Traits not undergoing natural selection have a normal distribution.

– highest frequency near mean value

– frequencies decrease toward each extreme value



Natural selection can change the distribution of a trait in one of three ways.

1) Stabilizing Selection- favors intermediate phenotype

- reduces variations




2) Directional Selection- favors phenotype at oneextreme

- leads to rapid evolution




3) Disruptive Selection- favors both extremephenotypes; intermediatephenotype is eliminated

- leads to evolution of two new species


Natural selection acts on different phenotypes in a population.

• Genetic variation leads to phenotypic variation.• The greater the genetic/phenotypic variations in a

population increases the chance that some individuals will survive

• Genetic variation is stored in a population’s gene pool.- gene pool = all the genes in all individuals in a

population

16 Evolution of Populations


• Allele frequencies measure genetic variation.

– measures how common allele is in population– can be calculated for each allele in gene pool– As allele frequencies and gene pools change over time,

the population evolve.



Genetic variation comes from several sources.

• Mutation is a random change in the DNA of a gene.

• Sexual reproduction results in new combinations of alleles. (crossing-over, independent assortment)

– can form new allele– can be passed on to

offspring if in reproductive cells

– usually occurs during meiosis – parents’ alleles

arranged in new ways in gametes



Genetic variation results in different types of adaptations.• Adaptation = variations that improve an organisms’

chance for survival and reproduction.

• Physical Adaptation1) Chemical: poison, toxin (ex: skunk)2) Mechanical:

Camouflage = adaptive coloration; blend in with the environment

Mimicry = resemble another species3) Structural: protective body forms (ex: fangs,

claws, spines)



Genetic variation comes from several sources.• Behavioral Adaptation

- actions taken by an organism to prolong survival (ex: hiding, running, migration, hibernating)



1) Genetic drift - changes allele frequencies due to random chance.

There are five factors that can lead to evolution.

- Genetic drift causes a loss of genetic diversity.- It is most common in small populations.



• A population bottleneck can lead to genetic drift. – It occurs when an event drastically

reduces population size.– The bottleneck effect is genetic drift

that occurs after a bottleneck event.

• The founding of a small population can lead to genetic drift.– It occurs when a few individuals start a new population.– The founder effect is

genetic drift that occurs after start of new population.



2) Gene flow - movement of alleles from one population to another- changes the allele frequencies in a gene pool• immigration = movement into the population• emigration = movement out of the population



• Positive mutations – help an organism better adapt to its environment

• Harmful mutations – organism dies and removes gene from population

3) Mutation- permanent change in DNA



4) Sexual selection - selects for traits that improve mating success.



5) Natural selection - selects for traits advantageous for survival.



The isolation of populations can lead to speciation.

• Populations become isolated when there is no gene flow. – Isolated populations adapt to their own environments.– Genetic differences can add up over generations.

• Speciation = the rise of two or more species from one existing species.

• A species is a group of organisms that breed with one another and produce fertile offspring.



The isolation of populations can lead to speciation. • Types of Isolation:

1) Geographical Isolation- isolated by physical barriers (ex: continental drift, earthquake, volcano)

2) Behavioral Isolation- differences in courtship and mating behaviors

3) Temporal Isolation- timing of reproductive periods prevents mating



Evolution through natural selection is not random. • Natural selection can have direction.• The effects of natural selection add up over time.



• Convergent evolution describes evolution toward similar traits in unrelated species.



• Divergent evolution describes evolution toward different traits in closely related species.

ancestor

red foxkit fox



Species can shape each other over time.

• Two or more species can evolve together through coevolution.– evolutionary paths become connected– species evolve in response to changes in each other– coevolution can occur in beneficial or competitive

relationships.



• Adaptive Radiation- Many species evolve from one species– ancestral species diversifies into many descendent

species– descendent species

usually adapted towide range ofenvironments



Species can become extinct.

• Extinction is the elimination of a species from Earth.

– occur at roughly the same rate as speciation

– usually affects a few species in a small area

– caused by local changes in environment



Evidence for evolution came from several sources.1) Fossils records

– provides a record of the earth’s past life forms• offers the most direct evidence for evolution• shows a pattern of development of early

ancestors to their modern descendants

17 The History of Life


• fossil – preserved or mineralized remains (bone, petrified tree, tooth, or shell) or imprint of an organism that lived long ago

• fossil record is incomplete – many organisms lived in places where fossils could not form –there are gaps in the record

17 The History of Life17 The History of Life


2) Biochemical Evidence – changes in DNA/amino acid/protein sequences- closely related organisms have similar DNA/amino acid/protein sequences and this also suggests common ancestry.



• Example: studying differences in hemoglobin between species



3) Comparative Anatomy– comparison of anatomy can reveal basic

structural similarities (even though the functions may be very different) indicating common ancestry

Human hand Bat wingMole foot



Homologous Structures - same structures but used for different functions through evolution

- ex. forelimbs in vertebrates all have the same basic bone structure

- have common ancestors(closely related)



Analogous Structures - different structures but used for same functions through evolution

- ex. bird wings, bat wings, insect wings- DO NOT have common ancestors( not closely related)

Bat wingFly wing



Vestigial Structures - structures that are reduced in size through evolution

- either have no use or have a less important function than they do in other related organisms

- provide evidence of an organism’s evolutionary past

- ex. hindlegs in whales, appendix in humans



4) Comparative Embryology– comparing embryos of related organism shows

similar developmental patterns- similar in embryos, but different in adult forms



- ex: the embryos of all vertebrates have similar characteristics during early development –all develop a tail, backbone, buds that become limbs, and pharyngeal pouches.


What is Evolution? Study of how things change over … is Evolution? • Study of how things change...

Documents

Transcript of What is Evolution? Study of how things change over … is Evolution? • Study of how things change...