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Topic 5
Evolution and Biodiversity
• There are 2 million named species on Earth,
with insects being the largest group.
• The organisms on the Earth today represent
less than 1% of all life that has ever existed.
• This Topic focuses on how natural selection
brings about evolution in organisms.
5.1 Evidence for Evolution
Charles Darwin and Alfred Wallace
Darwin explored the world from 1831-1836 and
came up with the theory of evolution by natural
selection.
In 1858, Darwin discovered that Wallace had
come up with a nearly identical theory.
What is evolution?
• The process of cumulative change in the
heritable characteristics of a population.
• Over time, changes can create a new species,
a process called speciation.
• The new species is different enough that it can
no longer reproduce with the original species.
• We will look at three phenomena that provide
evidence for evolution by natural selection.
Evidence for evolution
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The fossil record
Animal breeding
Homologous structures
Later in the unit we will look at DNA evidence
that supports natural selection
The Fossil Record
• Fossils are the petrified remains or traces of
plants and animals.
• The fossil record is the accumulation of
evidence from these remains and traces, such
as skeletons and footprints.
• Scientists who look for and study fossils are
called Paleontologists.
Evidence from the fossil record
• Life from 500 million years ago was vastly
different that today.
• Fish didn’t appear until around 500 million
years ago.
• None of todays top predators existed before
the dinosaurs.
• With a few exceptions, none of the organisms
of today had a similar form in the fossil record.
Ageing Fossils
• The age of a fossil can be determined by
looking at the ratios of certain isotopes.
• Example: Carbon-14 vs Carbon-12 also
written as 14C vs 12C.
• The more 14C a fossil has, the younger it is
because 14C is radioactive and slowly decays to
Nitrogen-14, or 14N.
• This process is called radioactive decay
• The speed or rate of this decay is referred to
as an isotope’s half-life.
• Half-life is defined as the time it takes half of
the parent isotope to decay to the more stable
daughter isotope.
• The half-life of 14C is 5730 years.
• After a long enough period of time, most of
the isotope is gone, so it is no longer accurate.
• Other isotopes with longer half-lives can be
used for older specimens, ex: 40K, especially
useful for aging rocks.
Artificial selection
• By choosing males and females with desired
characteristics, species can be changed to
reflect the desired traits.
• This is evidence that changes in organisms can
occur over a period of time. The choices are
being made by man but the same happens if
choices are made by nature.
Homologous structures
• Homologous structures are similar in form but
found in dissimilar species.
• A great example of this is the 5 fingered limb
found in humans, whales and bats.
• The function of the limbs is different, but the
basic structure is the same.
• This is viewed as evidence of a common
ancestor in the past.
Species Divergence
• Two populations of a species have become
different enough (diverged or separated) that
they can no longer inter breed and a new
species is created.
• Both species will continue on their own paths.
Adaptive Radiation
• Several different but similar species evolving
from a single species.
• Usually due to different environmental
conditions (niches).
• There is usually some kind of barrier keeping
the different species from each other,
mountains, body of water, etc.
• Darwin’s finches are an example
Continuous Variation and Gradual
Divergence
• A slow change in a species due to changing
environmental conditions, leading to eventual
formation of a new species.
• The new species has diverged from the
original species.
Transient Polymorphism
• Different forms of the same species.
• Usually the result of a mutation.
• The Peppered Moth is an example, having a
grey and a black form.
• Anywhere that there is a lot of pollution, the
black moth does better, otherwise the grey
moth is predominant.
• Transient has to do with predominant color
changing due to change in environment.
5.2 Natural Selection
• Darwin and Wallace offered Natural Selection
as the mechanism for evolution.
• The steps of natural selection are:
• Overproduction of offspring
• Variation in the offspring
• Competition or struggle for resources
• Some will do better than others and pass
traits on to their offspring.
Variation
• The process of sexual reproduction causes
variation in offspring.
• Variation is important to the survival of a
species.
• A change to the environment might kill many,
but some are likely to survive.
• What causes this variation? Mutation, meiosis
and sexual reproduction.
Mutation
• Mutations (changes to DNA) can cause genetic
disease and death, but sometimes the change
can be good.
• Mutations are rare and most cause no change
so mutation is not a strong creator of
variation.
Meiosis
• Creation of haploid gametes (2n
n)
• Each gamete is different due to random
assortment during Metaphase I
• Crossing over during Prophase I adds further
variation to the gametes.
Sexual Reproduction
• Asexual reproduction produces organisms that
are the same, they either all do well or they all
die. ( Irish potato famine)
• Variety in a population allows some to do well
when others don’t.
• In sexual reproduction, which sperm and
which egg form a zygote creates variation.
Adaptation
• An organism can’t adapt during it’s lifetime, it
is born with traits that are well adapted to the
environment it is born into.
• Natural selection tends to eliminate organisms
that aren’t well adapted to the environment
and support those who are.
• Scientists sometimes use the word “fit” to
describe an organism well adapted to it’s
particular environment.
Overproduction of offspring
• Maximizes the chance that some of the
offspring will survive.
• Due to limited resources, competition exists to
stay alive so the more there are, the greater
the odds are that some will survive.
Variation in the offspring
• Which organisms survive and which ones
don’t isn’t just by chance.
• Some offspring have variations that make
them more likely to survive and some less
likely to survive.
Competition or struggle for resources
• Due to the limited resources, organisms with
the good variations (more fit) will get more
and those with poor variations (less fit) will
get less.
Passing on Genes
• Because they are more likely to reach maturity
and reproduce, organisms with good
variations are more likely to pass their good
traits on to their offspring.
• Now there are more organisms with the good
variation.
• Over many generations, the accumulation of
changes causes evolution, the gene pool has
changed.
Modern Examples
• Pesticide resistance in rats
• Farmers use pesticide to kill rats
• Due to variation, a few of the rats are not affected by
the pesticide.
• These rats are better adapted to survive in the new
environment (pesticides)
• They thrive due to little competition.
• They pass on the pesticide resistance to their offspring.
• Farmer sees rats again and uses same pesticide but
nothing happens.
• A new pesticide is needed.
Modern Examples
• Antibiotic resistance in bacteria
• A person has a disease
• A doctor gives her an antibiotic to kill the
bacteria
• She gets better because most of the bacteria
are killed by the antibiotic.
• A few have a variation that allows them to be
unaffected by the antibiotic and they grow
and make the person sick again.
• Next time doctor gives her the antibiotic, it
doesn’t work.
• They need a new antibiotic.
• Because bacteria reproduce asexually, they
don’t show much variation but they can
become different two ways:
• Mutation and plasmid transfer.
• MRSA
Plasmid Transfer
• One bacterium donates a plasmid to another.
• Both bacteria develop openings in their cell
walls.
• A copy of a plasmid (DNA) is passed from one
to the other.
Examples
• MRSA Staph aureus
• Syphilis Treponema pallidum
• Tuberculosis Mycobacterium tuberculosis
• We need to limit our use of antibiotics to slow
down the process.
5.3 Classification
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The Binomial system for naming species.
Bi means two
Nomial means name
Two names
We are Homo sapiens
The first name is the genus of the organism
and it is always capitalized, the second name
is lower case and is the species name.
Binomial system
• In italics when typed or underlined when written
by hand.
• Most are Latin or Greek
• Credited to Swedish naturalist Carolus (Carl)
Linnaeus.
• Goals of the system:
• Each organism has a unique name
• Each name is universally understood
• Stability, people don’t change names without
valid reasons.
Naming New Species
• Originally there were only two kingdoms,
Plants and Animals.
• Over time, especially after the microscope,
new kingdoms were added.
• New organism has to be described, location
described, named using the rules of the
International Code of Nomenclature, an
example (holotype) put on display for other
scientists to see.
Scientific Names
• Sometimes scientific names are easy to
decipher because they contain the common
name:
• Amoeba amazonas
• Equus zebra
• Gekko gecko
• Gorilla gorilla
• Paramecium caudatum
Scientific Names
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Sometimes its difficult:
Apis mellifera
Aptenodytes patagonicus
Loxodonta cyclotis
Malus domestica
Hierarchy of Taxa
• Taxa (taxon) are categories that organisms are
put in.
• At the top, there are three domains:
• Archaea, Eubacteria, and Eukaryote domains
Archaea
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Single celled organisms that are not bacteria.
Very ancient
Live in very diverse habitats
Extremophiles – Thermophiles (heat loving)
Methanophiles (methane loving) and
halophiles (salt loving).
Eubacteria
• Bacteria
• Eukaryote
• Everything else, from single cell yeast to blue
whales.
7 Principal Taxa
• Each of the three domains is divided into 7
groups or taxa:
• Kingdom
Largest group Most variety
• Phylum
• Class
• Order
• Family
• Genus
• Species
Smallest group Most the same
Other ways of classifying
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Feeding – carnivore vs herbivore
Habitat – land dwelling vs aquatic
Daily activity – nocturnal vs diurnal
Risk – harmless vs venomous
Anatomy – vertebrates vs invertebrates
Common Ancestor
• One of the objectives of classification is to
show how organisms have descended from
common ancestors.
• Before knowledge of DNA, scientists used
characteristics of organisms.
Reclassification
• Due to increased knowledge, especially DNA
studies, many species have been identified as
being in the wrong genus and have been
moved.
• Example: Used to be a genus called aster that
had all the different aster species in it.
• Now there is another genus with some of the
asters in it.
Natural Classification
• Uses ancestry to group organisms together,
whereas artificial classification uses arbitrary
characteristics like does it taste good.
• Natural classification shows evolutionary links
and characteristics shared by groups.
Plant Phyla
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Bryophyta – mosses , very short height
Filicinophyta – ferns
Coniferophyta – produce cones, pines, cedars
Angiospermophyta – make flowers, fruit
Bryophytes
• Non-vascular, no method of transporting
materials through plant. No Xylem or Phloem.
• They have to be short due to the lack of ability
to transport material. Produce spores
Filicinophytes
• Are vascular
Do not produce flowers
• Recognizable by their triangular fronds made
up of many small, long, thin leaves. Make
spores
Conifers
• Leaves are in the form of needles or scales
• Produce seed cones
Angiosperms
• Produce flowers and fruit with seeds inside
• The flower is the reproductive organ
• The fruit is actually the ovary of the flower.
Animal Phyla
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Porifera – sponges
Cnidaria – jellyfish and coral
Platyhelminthes – flatworms
Annelida – segmented worms
Mollusca – snails, clams, octopuses
Arthropoda – insects, spiders and crustaceans
Chordata – animals with a backbone
Porifera
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Sponges are marine animals that are sessile.
No mouth of digestive tract.
Filter food out of the water.
No muscle or nerve tissue.
No distinct internal organs
Cnidaria
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Diverse so hard to easily characterize.
Corals, anemones, jelly fish,
They all have stinging cells called nematocysts
Use tentacles to catch food.
One opening, food in and waste out same
opening.
• Radial symmetry
Platyhelminthes
• Flatworms - Most notable is the tapeworm
• Only organ is a gut with opening at beginning
and end.
• They are flat so all cells can be close to the
surface for diffusion.
• They do not have segmented bodies.
Annelids
• Segmented worms like earthworms and
leeches.
• Have bristles on their bodies but sometimes
hard to see.
• Have a digestive or gastric tract with a mouth
at one end and an opening for waste at the
other.
Molluscs
• Snails, clams and octopuses
• Most make a hard shell out of calcium
• Have digestive tract with mouth and anus but
not segmented
Arthropods
• Have hard exoskeleton made of chitin,
segmented bodies, and jointed limbs.
• Includes insects, spiders, scorpions and
crustaceans such as crabs and shrimps.
• Most diverse group with over a million species
• Range in size from mites at 100 um to
Japanese giant spider crab at 4 meters
Chordata
• Have a notochord at some point of their
development.
• Notochord is a line of cartilage going down the
back that provides support.
• Most have a bony backbone and are called
vertebrates.
Vertebrates
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5 classes of vertebrates
Fish
Amphibians
Reptiles
Birds
Mammals
Fish
• Aquatic organisms with gills
• Skulls made of bone or cartilage.
• Most have jaws and teeth but some ( lamprey)
have suckers.
• Can have fins but no fingers or digits inside
the fins.
Amphibians
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Frogs and salamanders
Start their lives in the water
Young have gills but adults have lungs
Most can absorb oxygen through their skin
Most have 4 legs as adults but some have no legs.
Unlike reptiles, their eggs have no membrane
around the embryo
• Ectothermic – cold blooded
Reptiles
• Snakes, lizards, turtles and alligators
• Have a membrane around embryo just like
birds and mammals (amniote eggs)
• Unlike birds and mammals, they have scales
• Ectothermic
Birds
• Bipedal – two legs and wings, even if they
can’t fly.
• Have feathers, lay eggs with hard shells
• Hollow bones for lightness
• Beaks, no teeth
• High metabolism
Mammals
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Hair on their bodies
Females produce milk for their young
Most have 4 limbs and live on land
Whales and dolphins adapted to water
Thermoregulators, can maintain body temp at
a fixed level.
Dichotomous Key
• Step by step yes or no questions used to
determine the taxa of an organism.
• Asks a question about the organism. If yes,
you go to a certain question #2, if no, you go
to a different question #2, etc
5.4 Cladistics
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Characteristics used for classifying organisms:
Morphology – shape
Anatomy – number of petals, type of digestion
Cytology – structure of its cells
Phytochemistry – chemicals made by plants
for protection
• Chromosome number
• Protein and DNA sequences
Clades
• A clade is a group of organisms that have
evolved from a common ancestor.
• Evidence comes from DNA or amino acid
sequences.
• Primitive traits are same structure and
function and evolved early in the history of
the organism.
• Derived traits are same structure and function
but have evolved more recently.
• Example: leaves are a primitive trait in plants,
but flowers are a derived trait.
• When a group can be split into two parts, one
having a certain derived trait and the other
not, the group forms two separate clades.
• A clade is monophylitic, meaning it is the most
recent common ancestor and all of its
descendants.
Evidence for clades
• All organisms on earth use DNA for their
hereditary material and the same 20 amino
acids.
• This shows all life had a common ancestor.
• Phylogeny is the study of the evolutionary
past of a species.
• Species that are most similar (DNA) are more
closely related.
Evolutionary clock
• Changes to DNA over time happen and can be
used as a type of clock to estimate how much
time has passed since a split from a common
ancestor.
• If there are 26 DNA differences between A and
B, and 83 differences between A and C, you
can conclude that A split from C three times
longer ago than when it split from B.
Analogous vs Homologous Traits
• Used to put organisms into clades
• Homologous traits are traits derived from a
common ancestor.
• Example: 5 fingered limbs of humans, whales,
bats. Shape and number can vary but the
general format is the same for all.
• Example: eyes
• Can be seen in DNA also, same groups of code
• Analogous characteristics serve the same
function but not same structure and not from
a common ancestor.
• Example: wings of birds and wings of
mosquitoes
• Example: fins of fish and fins of dolphins
Cladograms
• A diagram showing cladistics, sort of like a
family tree.
• The point of branching, where the common
ancestor is located is called a node.
Cladograms and Classification
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Every cladogram is a working hypothesis
They change as scientific knowledge changes.
Example: Birds and dinosaurs
Reclassification occurs when new information
is gained.
• Moving species to reflect correct
monophyletic grouping is called
circumscription.
• Paraphyletic group isn’t a common ancestor and
all it’s descendants, something is omitted.
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Reptilia (green field) is a paraphyletic group comprising all
amniotes (Amniota) except for two subgroups Mammalia
(mammals) and Aves (birds); therefore, Reptilia is not a clade.
In contrast, Amniota itself is a clade, which is a monophyletic
group