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Biology 20Evolution

McGraw-Hill Ryerson Inquiry into Biology

Pages 72 to 151

I) Classification of OrganismsA) Taxonomic Systems

a) Introduction• First try to grasp the number of organisms that

exist• There is somewhere between 2 and 4.5

million different types of living plants and animals.

• There are several more million bacteria and microorganisms

• Also consider the fact that the majority of life that has existed on the planet is now extinct, well over 95% of all the life that has existed throughout the Earth’s history no longer does.

• Taxonomy is the science of classification according to the inferred relationships among organisms.

• We classify organisms for two main reasons:i) To identify organismsii) To recognize natural groupings of living things.

• Carl Linnaeus developed a system of classification that scientists currently use

• he based it on an organism’s structural and physical features thinking the more features organisms have in common the closer their relationship.

• we call this system of naming organisms binomial nomenclature

• Binomial nomenclature:• A method of naming organisms by using two

names, the genus name and the species name.• This is what is referred to as a plant or animals

scientific name.• Scientific names are always italicized or

underlined

ExampleCommon Name Scientific Name

House Cat Felius domesticusNeanderthal Homo neanderthalensisHuman Homo sapiens sapiens

• We use a dichotomous key to work out the scientific name of an organism.

b) The Levels of Taxonomy• there are seven main levels or taxa in the current

classification system.(taxa are categories used to classify organisms)

• the seven levels are:kingdom (the largest grouping)phylumclassorderfamilygenusspecies (the smallest grouping)

• the full classification of a human is:

Estimated Number of Members

CharacteristicsHumanLevel of Classification

1UsSapiensSpecies

1UsHomoGenus

5Chimps, gorillas, humans, and orangutansHominidaeFamily

233PrimatesOrder

4,629warm-blooded, presence of sweat glands (including those that produce milk), the presence of hair, three middle ear bonesused in hearing, and a neocortex region in the brain.

MammaliaClass

50’000having, at some time in their life cycle, a notochord, a hollow dorsal nerve cord, pharyngeal slits, an endostyle, and a post-anal tail.

ChordataPhylum

9,812,298Eukaryotic, multicelluar, heterotrophic,lack cell walls, are motile,

AnimaliaKingdom



1UsSapiensSpecies

1UsHomoGenus


233PrimatesOrder


MammaliaClass


ChordataPhylum

9,812,298Eukaryotic, multicellular, heterotrophic,lack cell walls, are motile

AnimaliaKingdom



1UsSapiensSpecies

1UsHomoGenus


233PrimatesOrder


MammaliaClass


ChordataPhylum

9,812,298Eukaryotic, multicelluar, heterotrophic,lack cell walls, are motile

AnimaliaKingdom

From Wikipedia

• The notochord is a flexible, rod-shaped body found in embryos of all chordates. It

is composed of cells derived from the mesoderm and defines the primitive axis of

the embryo. In lower vertebrates, it persists throughout life as the main axial

support of the body, while in higher vertebrates it is replaced by the vertebral

column. The notochord is found on the ventral surface of the neural tube.

From Wikipedia• Pharyngeal slits, found in both hemichordata and chordata, are used by organisms in feeding. The wall of the pharynx is perforated by up to 200 vertical slits, which are separated by stiffening rods.Rows of beating cilia cause currents of water to flow through the mouth, through the pharyngeal slits and out of the body through a hole in the body wall called the atripore. Small particles in the water are trapped by the cilia in different parts of the mouth chamber and separated into materials that the organism can eat.In primitive chordates the pharyngeal slits are used to strain water and filter out food particles; in fishes they are modified for respiration. Most terrestrial vertebrates have pharyngeal slits only in the embryonic stage.

From Wikipedia

• An endostyle is a longitudinal ciliated groove on the ventral wall of the pharynx which

produces mucus to gather food particles. It is found in urochordates and

cephalochordates, and in the larvae of lampreys. It aids in transporting food to the

esophagus. It is also called the hypopharyngeal groove. The endostyle in larval lampreys

(ammocetes) metamorphoses into the thyroid gland in adults, and is regarded as being

homologous to the thyroid gland in vertebrates. However, Dumont, et al. question

whether the endostyle in ammocetes is homologous with that of the urochordates and

cephalocordates.

From Wikipedia

• Human embryos have a tail that measures about one-sixth of the size of the embryo

itself. As the embryo develops into a fetus, the tail is absorbed by the growing body. The

developmental tail is thus a human vestigial structure. Infrequently, a child is born with a

"soft tail", which contains no vertebrae, but only blood vessels, muscles, and nerves,

although there have been a very few documented cases of tails containing cartilage or up

to five vertebrae.



1UsSapiensSpecies

1UsHomoGenus


233PrimatesOrder


MammaliaClass


ChordataPhylum


AnimaliaKingdom



233Forward-facing eyes, color vision,

opposable thumbs, flattened nails,

generalist teeth for an opportunistic,

complicated social organization

PrimatesOrder


MammaliaClass


ChordataPhylum


AnimaliaKingdom



1UsSapiensSpecies

1UsHomoGenus

5Chimps, gorillas, humans, and orangutans, Bonobo

HominidaeFamily

233Forward-facing eyes, color vision,

opposable thumbs, flattened nails,

generalist teeth for an opportunistic,

complicated social organization

PrimatesOrder


MammaliaClass

c) The Changing Kingdoms• Originally all organisms were placed into two

kingdoms, plants and animals.

• Then organisms with both animal and plant characteristics were discovered so a third kingdom was added, protista.

• when someone took a closer look at the protista kingdom they discovered lots of organisms with really unique characteristics so another kingdom was created called, monera.

• the monerans are what is known as the prokaryotes because they lack a true nucleus.

• a closer look at the monera kingdom shows that there are actually two distinct kingdoms in that one, they are called the:

• Archaebacteria• Eubacteria

• After further investigations we currently use a six kingdom system of classification

i) Eubacteriaii) Archaebacteriaiii) Protistaiv) Fungiv) Plantaevi) Animalia

i) Eubacteria• Simple prokaryotic organisms• either heterotrophs or autotrophs• can reproduce asexually• live nearly everywhere• cell wall present and contains peptidoglycan• examples:

bacteriacyanobacteria

ii) Archaebacteria• prokaryotes• heterotrophs• live in salt lakes, hot springs and animal guts• reproduce asexually• have a cell wall with no peptidoglycan• examples:

methanogensextreme thermophiles, extreme halophiles

iii) Protista• eukaryotic (has a true nucleus)• majority are single celled.• mixture of autotrophs and heterotrophs and

some are both.• reproduce asexually and sexually• live everywhere• no cell wall• examples:

algaeprotozoa

iv) Fungi• eukaryotic• all are heterotrophs• reproduce asexually and sexually• most are terrestrial• has a cell wall• examples:

mushroomsyeastmoulds

v) Plantae• eukaryotic• autrotrophs• reproduce asexually and sexually• terrestrial and aquatic• has a cell wall• examples:

mossesfernstrees

vi) Animalia• eukaryotic• heterotrophs• most reproduce sexually• terrestrial and aquatic• no cell wall• examples:

spongesreptilesmammals

d) Phylogeny• the history of the evolution of organisms is called the

phylogeny.• The evolutionary history of different organisms

is illustrated by a phylogenetic tree or cladogram.

Cladogram (Phylogenetic Tree) Example

II) Developing the Evolutionary TheoryA) The People Involved

i) Galen• First to collect and document anatomical data of different animalsii) Andreas Vesalius• Started comparative anatomy.• Only trust what you can observe.• Recognized humans had few unique and many common traits with

animals.iii) Reverend William Paley• Founded scientific theology• Started the process of wanting to know the function of different parts

of the body.iv) Nicholas Steno• Founded paleontology.• Proposed that fossils were once living creatures.• Came up with the law of Superposition.v) Carolus Linnaeus• Developed a way to classify living and extinct organisms.• Slotted humans in his classification scheme as if they were just like

any other animals.

vi) Buffon

• Thought the Earth to be old than originally thought.

• Established that life on the Earth was changing.

vii) Thomas Malthus

• Established that natural resources will limit the reproductive rates

and survival of plants and animals.

• There are limited amounts of resources to support organisms that can

reproduce without limits.

viii) George Cuvier

• There are periodically sudden changes to the Earth that wipe out a

number of species (mass extinction events)

ix) Jean Baptiste Lamarck

• Species change over time.

• The theory of use and disuse. A species that uses an anatomical

feature will have it grow strong and that will be passed on to its’

offspring. A species that does not use a feature will have that feature

wither away and it will not be passed on to it’s offspring.

• Inheritance

• Nature drives life from simpler forms to more complex forms.

x) Karl von Baer

• Defeated the idea of recapitulation.

• The concept that as an embryo we pass through different

“lower” life form stages (we recapitulate it) on our way to

being a higher more complex life form.

xi) William Smith

• Create the geological time scale.

• The age of the Earth and life on it is much older than anyone has

previously thought.

xii) Charles Lyell

• The Earth is gradually changing through a uniform and constant

mechanism. (uniformitarianism)

xiii) Gregor Mendel

• Traits can be inherited. Some traits are dominant and some are

recessive.

B) The Evolutionary Theory

i) Definitions

– In the life sciences, evolution is a change in the traits of living organisms over generations, including the emergence of new species.

– Natural selection is the differential survival and reproduction of organisms with genetic characteristics that enable them to better utilize environmental resources

ii) Darwin and Wallace

• Darwin and Wallace developed the theory of evolution through natural selection

– The reason why Charles Darwin is so famous is that he wrote the book On the Origin of Species by Means of Natural Selection which sold out on the first day it went on sale.

iii) The Theory of Evolution by Natural Selection

• Three observations made by Darwin and Wallace

– Individuals within any species exhibit many inherited variations

– Every generation produces far more offspring than can survive to

reproduce.

– Populations of species tend to remain stable

• These three observations led to three inferences

– Individuals of the same species are in a constant struggle for survival.

– Individuals with more favorable variations are more likely to survive

and pass these variations on. Survival is not random. This is natural

selection.

– Since individuals with more favorable variations contribute

proportionately more offspring to succeeding generations, their

favorable inherited variations will become more common. This is

evolution.

C) The Evidence

– All successful scientific theories can be supported by observable

evidence.

– The evidence that is easiest to understand that supports the

evolutionary theory falls into three categories:

• Paleontology

• Biology

• Biochemistry

i) Paleontology

• Paleontology is the study of fossils.

• Scientists have found approximately 250’000 fossils species

(only a fraction of organisms that have lived on Earth form fossils)

• Fossils provide us with direct physical evidence of the patterns of past life.

• What we have found:

– Different species lived on Earth at various times in the past.

– Very few of the species that were alive one million years ago are alive today.

– Almost all the species that have lived are now extinct.

– Complexity of living organisms is generally increasing.

– Living species and their most closely matching fossils are typically located in the same geographical region.

• For the fossilization process to occur the Earth would have to be much older than

originally predicted.

– Scientists use radiometric dating to determine the age of rocks and fossils.

• Radiometric dating is a variety of absolute dating methods based on the

rates of the transformation of an unstable radioactive isotope into a stable

element.

• The most common example is carbon-dating.

– Carbon-dating is based on the fact that all living organisms have two

types of carbon inside them, regular carbon (12C) and radio-active

carbon (14C).

– Once the organism dies the 14C decays into nitrogen (14N).

– It takes 5,730 years for half a 14C sample to decay into 14N.

– By measuring the amount of 14C remaining in a specimen and

comparing it to the amount of 12C one can tell how long ago the

organism died

Table 1. Half Lives for Radioactive Elements

5730 yearsNitrogen 14Carbon 14

4.47 billion yearsLead 206Uranium 238

704 million yearsLead 207Uranium 235

14 billion yearsLead 208Thorium 232

48.8 billion yearsStrontium 87Rubidium 87

1.25 billion yearsArgon 40 Potassium 40

Half LifeStable DaughterRadioactive Parent

• With the ability to date specimens that are very old we can build a geological calendar or timescale of the Earth.

ii) Biogeography

• Biogeography is the study of geographic distribution of life on Earth.

• Fossil distribution corresponds to a planet whose continents are constantly

in motion.

Pangaea

225 million years ago

• 150 million years ago pangaea was in full break up.

– Fossils of similar species that are older than 150 million years are

found on many different continents of today’s world.

• These species evolved when all the land masses were together and

their fossils were carried along with the moving continents.

– Fossils younger than 150 million years do not show the same

similarities because those animals evolved in isolation after the break

up of pangaea.

• Evolution and Geographic Distribution

– If evolution has been happening it should be able to explain how an organism came to be in a certain area.

– Organisms that are most closely related tend to be found in the same area.

• Two populations evolving in isolated regions may follow very different evolutionary paths.

This is called divergent evolution and is usually caused by physical barriers.

– Produces homologous structures. Having common origin but different uses today.

Homologous structures: vertebrate limbs: human, dog, horse, whale

• There may also be convergent evolution in which dissimilar organisms evolve toward

a similar form.

– Produces analogous structures. Have different origins but evolve toward a similar form

due to selective pressure.

Analogous structures: wing of an insect, bat, bird and pterosaur.

iii) Biology

a) Embryology/Comparative Anatomy

• Species that descend from a common ancestor should show

similarities in structure.

• New adaptations for an old trait may result in the trait being

modified but it may still exist in some form.

• Organs that no longer have an apparent use due to evolution are

called vestigial organs.

– Such as the appendix in humans & hip bones in whales.

• Many species share traits in the embryonic stages of development

(gill slits, post anal tails)• Embryos also show traits that

are a throw back to earlier forms of the species.

embryonic humans having gills

b) Biochemistry

• Scientists can look at an amino acid sequence in a particular protein

common to many different organisms to look for similarities.

– Animals with a closer amino acid sequence will be closer

evolutionarily

– Animals with a differing amino acid sequences will be farther apart

evolutionarily.

• Hemoglobin, the molecule that carries oxygen in an animals body

is an example.

– It is a protein that has been around a long time.

– Many animals have it.

Human

Based on physical appearance place these animals on the phylogenetictree.

• Lamprey

• Bird

• Dog

• Frog

• MacaqueCommon

Ancestor

Differences in amino acid sequences in a

portion of hemoglobin protein reflect the degree

of similarity among different species

Human Macaque

DogBird Frog

Lamprey

8

32

45

67

125

Common

Ancestor

• Comparing the DNA (deoxyribose nucleic acid) sequences among different

species exhibits the same relationship that is observed in protein

sequencing.

– The more related evolutionarily the animal the more similar its DNA

is.

• All organisms have certain biochemical properties in common:

– They are DNA or RNA based.

– They use amino acids and proteins as building blocks.

– They use glycolysis as a method of energy production.

(every one produces energy in the same manner, some have other

mechanisms to be more efficient, cellular respiration)

Sea Cabbage

Sea Cabbage

Broccoli

Sea Cabbage Broccoli

Cauliflower

Sea Cabbage Broccoli Cauliflower

Brussels Sprouts

Sea Cabbage Broccoli Cauliflower Brussels Sprouts

What is the connection?

iv) Artificial Selection

• Broccoli, cabbage, brussels sprouts, cauliflower, kale are all

products of artificial selection over many generations of sea

cabbage.

– Artificial selection is the process of humans selecting and

breeding individuals with the desired traits.

• Most widely used in agriculture

– Humans can adapt the evolution process of natural

selection to artificially select and create new species.

“what works in nature works in the lab (or farm)”

II) The Big Picture

A) The Process.

The Evolutionary dance works like this:

Step 1. You have many members of a species, we call this a

population, that is full of variation or diversity.

Step 2. The environment changes, this makes it difficult for all the members

of a population to survive, we call this a selective pressure.

examples: loss of food, climate change, disease

Step 3. Only those members that are best fit (fitness) or adapted for the

new environment survive and reproduce, we call this natural selection.

Step 4. Over time the traits that make an organism the best fit for the

environment accumulate and a new species emerges (speciation), this is

evolution.

• Some important points:

– Variation or diversity in the population must be present before the environment changes

• This means the solution to the problem that the population will face has to be present before the problem is known.

• No one can predict what the selective pressure will be.

• Populations that are not diverse are more likely to go extinct.

• The traits that a species has that will make it the best fit for it’s new environment come about through changes in the DNA.

• It takes many generations for those traits, or changes in the DNA, to accumulate and form a new species.

– Animals with long life spans evolve slower than those with shorter life spans.

» compare a bacteria (20 minutes) to a human (75 years)

B) The Source of Change

• variation in a species comes about through two ways:

– Sexual reproduction

– Mutations in the genetic code

i) Mutations

– All the characteristics organisms have are encoded for in genes which are

discrete areas of DNA (or RNA) on your chromosomes

– Genotype: this is the actual genetic blueprint of an organism.

– Phenotype: this the physical product of the genotype, it is what we

see.

» The genotype of her eyes causes them to have a blue

phenotype.

– Genes are found in the chromosomes, which are found in the nucleus

(eukaryotes) or nuclear area (prokaryotes) of a cell.

• Genes (DNA) are made from four bases:

adenine (A), thymine (T), cytosine (C), guanine (G)

• Every organism that exists in our world and that has existed has been

encoded from a genetic code that is made up of only four different

kinds of chemicals.

– But those 4 bases can be used billions of times.

• The DNA of an organism will normally remain constant through out its

life.

– Sometimes DNA can change:

» Bases randomly change.

» Sections of DNA are deleted or inserted.

» Sections of DNA can be duplicated.

– These mutations are rare. But over many generations and millions

of years they add up.

• a mutation in the DNA can have one of three effects on an organisms fitness (reproductive success).

no effect, we call this a neutral mutation.

it can enhance an organism’s fitness, this is a beneficial mutations.

it can reduce an organism’s fitness, this is a harmful mutation.

(most mutations are neutral or harmful)

• some common mutations misconceptions:

misconception: mutations occur when needed in response to the environment.

the truth: mutations are random, there is no design to them.

misconception: harmful mutations can accumulate in a species.

the truth: harmful mutations are selected against reducing or eliminating an individual’s chance of reproductive success. No accumulation occurs.

misconception: because mutations are random, evolution is random.

the truth: beneficial mutations may be random but they are selected for by the environment.

ii) Sexual Reproduction

• asexual reproduction

• is the production of offspring from a single parent; offspring inherit the genes of that parent only.

example: bacteria

• sexual reproduction

• the production of offspring by the union of sex cells from two different parents, the offspring inherit a combination of genes from both parents.

example: animals

• asexual reproduction produces very little variation compared to sexual

reproduction.

• because of the variation produced sexually-reproducing species have

many traits that natural selection can act upon.

• what makes sexual-reproducing species so variable?

i) Sexually-reproducing species have two copies of each gene.

• each parent contributes one copy of each gene to the offspring.

– The offspring therefore has a different combination of genes than either parent, therefore it has its own set of unique traits.

ii) Random-assortment

• the assortment of genes that an offspring inherits from either parent is determined randomly.

– Other then identical twins, siblings produced from sexual reproduction are unique with their own traits.

iii) Mates

• sexually-reproducing species can choose different mates.

– each combination of parents will give rise to different combinations of genes and traits in the next generation.

• Darwinian Evolution and Genetic Mechanisms

Genetic MechanismsDarwinian Evolution

• inherited characteristics (phenotypes) are determined by genes (genotypes)

Inherited characteristics

• individuals of the same species differ from one another because of different combinations of genes. The genetic makeup of all individuals in a population is called a gene pool.

Population variability

• new traits can arise when genes become mutated.Source of new variations

• some genes determine traits that make an individual better suited for survival and reproductive success. Individuals with these traits will produce more offspring that may inherit these genes.

Natural selection

• over many generations individuals carrying advantage genes of favourable traits become more numerous in the population. Evolution is the change in the population’s gene pool.

Evolutionary change

C) Speciation and Evolution

i) Allopatric Speciation

• Natural selection provides an explanation for how species become better adapted to their environment.

• The process of forming a new species and from that, entirely newgroups of living organisms (evolution) is thought to occur through allopatric speciation.

The Three Steps to Allopatric Speciation

1) A physical barrier separates a single interbreeding population into two or more groups that are isolated from each other.

• Each population develops its own variation through unique mutations.

2) Natural selection works on the separate groups independently, resulting in inherited differences in the two populations.

• The two groups evolve independently because of different environments causing different selective pressures.

2) Natural selection works on the separate groups independently, resulting in inherited differences in the two populations.

• The two groups evolve independently because of different environments causing different selective pressures.

3) Over time accumulated physical and/or behavioural differences between the populations become very pronounced.

• If the groups were to come back together they would no longer be sexually compatible.

• They have formed two or more distinct species.

• New species have developed.

C) Speciation and Evolution

• physical and behavioural barriers that can lead to speciation can be:

• mountain ranges

• oceans

• rivers

• canyons

• dams

• highways

• mating rituals

• being nocturnal

• speciation can also occur in a single geographic area when one population splits into a distinct breeding population.

• this frequently occurs in plants.

ii) Rate of Evolution

• at first scientists thought change to species occurred at a slow and steady rate.

• this is called the Theory of Gradualism

Theory of gradualism is the idea that speciation takes places slowly.

• there are three patterns in the fossil record that make the Theory of Gradualism doubtful:

• many species evolve very rapidly in evolutionary time.

• speciation usually occurs in small isolated populations, so intermediate fossils are very rare.

• after an initial burst of evolution , species are well adapted to their environment and do not change significantly over long periods of time.

• this lead to the Theory of Punctuated Equilibrium

The idea that species evolve rapidly, followed by a period of little or no change.

iii) Macroevolution

• macroevolution are periods in the history of the Earth where evolution occurred relatively quickly or quite profoundly resulting in changes in the taxaat levels higher than that of just species.

• it follows major extinction events

• it is recognized in the fossil record as periods of accelerated divergent evolution.

iv) Testing Evolution

• all scientific theories are judged by their ability to:

a) Account for old and new evidence

b) Make testable predictions.

• It is possible to see how any trait of any organism makes it a better fit for its environment and reproductively more successful.

Biology 20 Evolution - Wikispaces20i...added, protista. • when someone took ... • the monerans are what is known as the prokaryotes ... – Natural selection is the differential

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