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Evolution occurs when heritable characteristics of a species change
Evolution concerns itself with heritable characteristics passed down through
generations not acquired characteristics in a life time by an individual
Mechanism of evolution is natural selection
Gradual development of life in geological time, from earliest beginnings to
now; development of organisms by accumulation of genetic differences over
long periods of time through natural selection and chance variation
The fossil record provides evidence for evolution
First half of 19th century, eras were named because rock depositions were
worked out
20th century, radioisotope dating revealed ages of rock and fossils; fossil
research is known as paleontology
Evidence
 Bony fish occurred 420 million years ago, amphibians 340, reptiles
320, birds 250, and placental mammals 110
 Plants appeared before animals, plants on land before animals on
land, plants suitable for pollination before pollinators
 Horses, donkeys, and zebras are closely related to Equus species
which as rhinos and tapirs; fossils from 60mya link them to
Hyracotherium, an animal like rhino
Selective breeding of domesticated animals shows that artificial
selection can cause evolution
Artificial selection caused by humans to obtain domesticated breeds; it is the
repeated selection of individuals with desired traits for breeding
Shows that selection can cause changes and evolution; but its not proof for
natural selection or natural evolution; its proof of change
Charles Darwin bred pigeons; all of them descended from rock dove
Evolution of homologous structures by adaptive radiation explains
similarities in structure when there are differences in function

Analogous Structures
 Similarities in structure between organs which are superficial
 Structures are actually very different but end up looking similar
because they perform the same function (wings of bat and insect)
Homologous Structures
 May look superficially different and perform different functions, but
have a “unity of type”
 Eg: Forelimbs of horses, humans, moles, and bat
 Occupy similar positions on different organisms
 Then over time function changes and structures diverges; this is
known as adaptive radiation
Rudimentary Organs
 Reduced structures that serve no function; vestigial organs
 Eg: appendix; thigh bones in whales and some snakes
 Structures that no longer have a function and so are being
gradually lost


More Evidence

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Populations of a species can gradually diverge into separate
species by evolution
Organisms will evolve differently if two populations separate and can’t
interbreed, and natural selection acts differently on them
After some time, they will be recognizably different; when they are
merged and are given the chance to interbreed they might not breed; this
process of separation is speciation
Often occurs when population extends to an island; explains large
numbers of endemic species on islands
Endemic species is only found in a certain area
Continuous variation across the geographical range of related
populations matches the concept of gradual divergence
Eg: Red grouse of Britain and willow ptarmigan of Norway
They are sometimes classified as separate species and sometimes as
varieties of Lagopus lagopus
Species can divere over long periods of time; the decision to lump
populations together or split them is arbitrary
Originally, a population shares a gene pool; but once separated mutations
could trigger changes in one of the populations without changing the
other
New population could come from a larger group and the new group may
have very different features from the older larger group

Natural Selection and Variation

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During Industrial Revolution, air pollution such as gases and soot
blackened the trees and killed off the mosses and lichen
The number of dark varieties of some 80 species of moth increased in
the habitats
The melanic form of the Biston betularia increased in industrial areas, but
low in non polluted areas where a lighter speckled form of the moth was
common
The melanic form became dominant in industrial areas as it could easily
camoflague and wasn’t as preyed upon
...

Acquired characteristics are not significant and cannot be passed down
Natural selection increases the frequency of characteristics that
make individuals better adapted and decreases the frequency of
other characteristics leading to chances within the species
There is an increase in the population with characteristics that make them
well adapted; characteristics of population gradually change
Major changes occur over long time peridos and many generations and so
usually can’t be seen by humans

Galapagos Finches and Antibiotic Resistance 6/11/2016
7:49:00 PM

Darwin observed size and shape of beaks in finches and they varied
between 14 species but had other similarities between the species
Peter and Rosemary Grant have shown that beak and diet are closely
related and when changes, so does the other
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Antibiotic resistance occurs due to genes in bacteria and so it is
inheritable;
Evolution of multiple antibiotic resistance strains has occurred in just a
few decades and this is because:





Widespread use of these antibiotics, both for disease and animal
feeds
Bacteria can reproduce very quickly
Populations of bacteria are often huge, increasing the chance of
a gene for antibiotic resistance being formed through mutation
Bacteria can pass genes on to other bacteria through several
ways, including plasmids

Binomial System

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Trends in antibiotic resistance:
 After an antibiotic is introduced and used on patients, bacteria
showing resistance appear within a few years
 Resistance to the antibiotic spreads to more and more species of
pathogenic bacteria
 In each species the proportion of infections that are caused by a
resistance strain increases
Biodiversity is the total number of different species living in a defined
area or ecosystem

The binomial system of names is universal and has been agreed
and developed at a series of congresses
The binomial system is also called binomial nomenclature; consists of two
words
The first name is a genus name (a group of species that share certain
characteristics); the second name is the species name
Rules:




Genus name begins with upper case and the species name is
lower case
Shown in italics
After being fully displayed once, it can be abbreviated by writing
the genus letter and the whole species name (L
...

Differences in the gene sequence and thus the amino acid sequence come
from mutations, which accumulate over time
There is evidence that mutations occur at a roughly constant rate, so it is
possible to use them as a molecular clock
The number of differences in sequence can be used to deduce how long
ago species split from a common ancestor
Traits can be analogous or homologous


Homologous structures are similar because of similar ancestry;
the structure may not look the same but it will have evolved
from a similar ancestor



Analogous structures are similar because of convergent
evolution; they may look the same but that doesn’t mean they
come from a common ancestor, rather they developed
independently

Failures in correct distinguishing have led to mistakes in classifications;
thus, the morphology of organisms is rarely used, instead the inner
biology is taken into account (gene sequences and amino acid sequences)

Cladograms

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Cladograms are tree diagrams that show the most probable
sequence of divergence in clades
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