EvolutionDiversity of Life

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•Evolution is the slow, gradual change in a population of organisms over a long period of time

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Lamarck’s Theory of Evolution• One Of First

Scientists To Understand That Change Occurs Over Time

• Stated that Changes Are Adaptations To Environment acquired in an organism’s lifetime

• Said acquired changes were passed to offspring 3

Lamarck’s Theory of Evolution

• Inheritance of Acquired Characteristics

• Proposed That By Selective Use Or Disuse Of Organs, Organisms Acquired Or Lost Certain Traits During Their Lifetime

• These Traits Could Then Be Passed On To Their Offspring

• Over Time This Led To New Species

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Lamarck’s Theory of Evolution• Use & Disuse -

Organisms Could Change The Size Or Shape Of Organs By Using Them Or Not Using Them

• Blacksmiths & Their Sons (muscular arms)

• Giraffe’s Necks Longer from stretching)

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Lamarck’s Theory of Evolution

• Inheritance Of Acquired Traits– Traits Acquired During Ones

Lifetime Would Be Passed To Offspring

7Clipped ears of dogs could be passed to offspring!

Lamarck’s Mistakes

• Lamarck Did NOT Know how traits were inherited (Traits are passed through genes)

• Genes Are NOT Changed By Activities In Life

• Change Through Mutation Occurs Before An Organism Is Born

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Darwin’s Conclusion

• Production of more individuals than can be supported by the environment leads to a struggle for existence among individuals

• Only a fraction of offspring survive each generation

• Survival of the Fittest

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Darwin’s Observations

• Individuals of a population vary extensively in their characteristics with no two individuals being exactly alike.

• Much of this variation between individuals is inheritable.

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Darwin’s Conclusion

• Individuals who inherit characteristics most fit for their environment are likely to leave more offspring than less fit individuals

• Called Natural Selection

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•The The unequal ability of individuals unequal ability of individuals to survive and reproduceto survive and reproduce leads to leads to a gradual change in a population, a gradual change in a population, with favorable characteristics with favorable characteristics accumulating over generations accumulating over generations (natural selection)(natural selection)•New species evolveNew species evolve

Darwin’Darwin’s s

Theory Theory of of

EvolutioEvolutionn

EVOLUTIONEVOLUTIONEvidence and Evidence and

Mechanisms for Mechanisms for EvolutionEvolution

Evidence for Evolution

Evidence in organisms:• 1. Biochemistry & DNA• 2. Fossil Evidence• 3. Embryology• 4. Structures

• Our genes provide an ‘evolutionary record’• If we evolved from a common ancestor:

– We should have same genetic molecule (DNA)– We should use the DNA in the same way

(dogma)– Portions of our DNA should be the same (and

they are)

• Closely related organisms share large portions of

DNA (amino acid) sequence…

1. Biochemistry & Molecular Biology

87 88 89 90 91 92 93 94 95 96 97 98 99 100 101

Human THR LEU SER GLU LEU HIS CYS ASP LYS LEU HIS VAL ASP PRO GLU

Chimpanzee THR LEU SER GLU LEU HIS CYS ASP LYS LEU HIS VAL ASP PRO GLU

Gorilla THR LEU SER GLU LEU HIS CYS ASP LYS LEU HIS VAL ASP PRO GLU

Rhesus Monkey GLN LEU SER GLU LEU HIS CYS ASP LYS LEU HIS VAL ASP PRO GLU

Horse ALA LEU SER GLU LEU HIS CYS ASP LYS LEU HIS VAL ASP PRO GLU

Kangaroo LYS LEU SER GLU LEU HIS CYS ASP LYS LEU HIS VAL ASP PRO GLU

102 103 104 105 106 107 108 109 110 111 112 113 114 115 116

Human ASN PHE ARG LEU LEU GLY ASN VAL LEU VAL CYS VAL LEU ALA HIS

Chimpanzee ASN PHE ARG LEU LEU GLY ASN VAL LEU VAL CYS VAL LEU ALA HIS

Gorilla ASN PHE LYS LEU LEU GLY ASN VAL LEU VAL CYS VAL LEU ALA HIS

Rhesus Monkey ASN PHE LYS LEU LEU GLY ASN VAL LEU VAL CYS VAL LEU ALA HIS

Horse ASN PHE ARG LEU LEU GLY ASN VAL LEU ALA LEU VAL VAL ALA ARG

Kangaroo ASN PHE LYS LEU LEU GLY ASN ILE ILE VAL ILE CYS LEU ALA GLU

Cladogram – a graphic representation that shows relatedness of organisms

• Fossils – any trace left by a previous organism

• Rocks, ice, amber, bogs, tar, etc.• Most are preserved in

sedimentary rocks• Oldest rocks (fossils) have

simplest life forms and found deeper in the crust

2. FOSSIL EVIDENCE FOR EVOLUTION

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Evidence for Evolution – The Fossil RecordEvidence for Evolution – The Fossil Record

• Early embryos of different mammal species look very much alike – they share common features, such as gills, eyes, ear holes, tails

3. Developmental Biology

• Homologous structures: Share same common origin or structure, but may have different functions.

• For example: same bone structure found in a human arm, bat wing, dolphin flipper, bird wing…

4. Comparative Anatomy

• Analogous structures: organs that have similar functions in different organisms, but do not share a common evolutionary origin or same structures

• For example:Wings of insects vs. wings of birds

• Vestigial strucutres: organs or parts of organs that are non-functional and degenerate

• For example: wisdom teeth, appendix

• Vestigial leg bones in snakes and whales

Vestigial organs

What does this say about whales?

Why do snakes have two lungs but only one is functional?

• Natural Selection• Mutation• Genetic Drift• Gene Flow

Four Types of Evolutionary Mechanisms

• There is variation in traits.For example, some beetles are green and some are brown.

• There is differential reproduction.Since the environment can't support unlimited population growth, not all individuals get to reproduce to their full potential. In this example, green beetles tend to get eaten by birds and survive to reproduce less often than brown beetles do.

• There is heredity.The surviving brown beetles have brown baby beetles because this trait has a genetic basis.

• End result:The more advantageous trait, brown coloration, which allows the beetle to have more offspring, becomes more common in the population. If this process continues, eventually, all individuals in the population will be brown.

If you have variation, differential reproduction, and heredity, you will have evolution by natural selection as an outcome. It is as simple as that.

Natural Selection

• Stabilizing – Baby weight– Pays to be average

• Directional– Peppered moth– Pays to be different

• Disruptive– Lizards on volcanic

rock

Types of Natural Selection

• Disruptive selection: selection that tends to divide a population into two categories

• A species of spadefoot toads that lives in Oregon has two color phases that are genetically determined so that these toads are either light or dark in color. Spadefoot toads live in arid regions and like most prey animals are active at night. A variety of predators feed on these toads. Spadefoot toads prefer dry habitats and are mostly nocturnal. These toads burrow into the ground to keep from drying out during the day and can stay underground for long periods of time when conditions are too dry.

In the Diamond Craters area of Oregon the soil is very dark due to the dark volcanic material deposited in the area. Almost all of the spadefoot toads living in this area are the dark variety while those from the surrounding desert are the light variety.

Disruptive

• directional selection: selection that favors individuals with an extreme value of some feature, so that a population will shift in one direction

• African elephants typically have large tusks. The ivory in the tusks is highly valued by some people, so hunters have hunted and killed elephants to tear out their tusks and sell them (usually illegally) for decades. Some African elephants have a rare trait -- they never develop tusks at all. In 1930, about 1 percent of all elephants had no tusks. The ivory hunters didn't bother killing them because there was no ivory to recover. Meanwhile, elephants with tusks were killed off by the hundreds, many of them before they ever had a chance to reproduce.

Directional

Stabilizing selection: selection that tends to maintain some feature of a population at an average value

• Inheritable change in genetic material– Ex: bacteria and viruses

Mutation

• Change in allele frequency due to chance– Ex: disease, population crash,

natural disaster

Genetic Drift

• Movement of alleles in and out of a population

• Ex: immigration or emigration of organisms

Gene Flow

• Adapt if the genes are already present

• Migrate to another area• Become extinct

Selection Pressures may cause the organism to:

• ADAPTATIONS are traits that promote the survival and reproductive success of an organism in a particular environment.

• Specific behavioral, Physiological, Physical, Chemical, Mimicry that arise during evolution, as a response to specific environmental pressures.

ADAPTATIONS

• Physiological – bodily processes– Ex: sweating, fever

• Behavioral– Ex: hibernation,

bird calls for mating

Behavioral and Physiological Adaptations

• Thorns on a cactus to avoid predation

• Cuticle on a leaf to prevent water loss

Physical Adaptations

• Release of a chemical substance to ward off predators– Ex: poison ivy,

skunks releasing odor, squid releasing ink

Chemical

• Mimicry: a harmless species may resemble a dangerous species. – Ex: Monarch butterfly

is toxic, but Viceroy is not.

– Ex: Coral snake: venomous vs. impostor

• “Red on black, venom lack. Red on yellow, kill a fellow”

Mimicry and protective coloration

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• Geographic isolation – a physical barrier prevents reproduction

Migration Types

Reproductive isolation – physical changes prevent reproduction

•Lack of "fit" between sexual organs:Hard to imagine for us, but a big issue for insects with variably-shaped genitalia!

•Offspring inviability or sterility:All that courting and mating is wasted if the offspring of matings between the two groups do not survive or cannot reproduce.

These damselfly penises illustrate just how complex insect genitalia may be.

Temporal isolation – timing of mating prevents reproduction

The evolution of different mating location, mating time, or mating rituals:Genetically-based changes to these aspects of mating could complete the process of reproductive isolation and speciation. For example, bowerbirds (shown below) construct elaborate bowers and decorate them with different colors in order to woo females. If two incipient species evolved differences in this mating ritual, it might permanently isolate them and complete the process of speciation.

All of which can lead to speciation – the development of a new species

• The loss of a species due to selective pressures

• Variation – difference within species reduces the chances of extinction

• Biodiversity – differences among species

Extinction

• Divergent evolution – a single species becomes adapted to different environment and becomes less alike

• Darwin believed that at one time, all the finches originated from one species.

• Due to their variation in their beak sizes, the finches fed on different diets.

• In order to survive, the finches moved to areas where their diet could be found.

Darwin’s Finches – speciation and divergent evolution

• Coevolution: the long term evolutionary adjustment of one group of organisms to another.

• Coevolution is a reciprocal process in which characteristics of one organism evolve in response to specific characteristics of another

Coevolution

• Mutual evolutionary influence between two species (the evolution of two species totally dependent on each other). Each of the species involved exerts selective pressure on the other, so they evolve together.

• For example: Moth and Yucca plant• Yucca flowers are a certain shape so only that tiny

moth can pollinate them. The moths lay their eggs in the yucca flowers and the larvae (caterpillars) live in the developing ovary and eat yucca seeds.

Coevolution

• There’s ANTS in PLANTS!• Acacia trees and ants –

coevolution.

Examples of co-evolution: symbiosis

• Flowers & insects/birds coevolution for pollination.

Pollination: coevolution of plants and insects