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SCI 102
Major themes in Biology
Unity and diversity among organisms
Unity : the following and many other properties are
shared by all organisms;
 cell is the basic unit
 Have DNA as genetic material
 Life requires energy transfer
 Structure and function are
correlated, …
Core theme in Biology
 1.8 million species have been identified and named
 Estimated number of species is 10-100 million
Along with a vast diversity we find many shared
Evolution can explain both unity and diversity
Core theme of biology is EVOLUTION!!!
Observations of Charles Darwin
 Org’s are strikingly well suited to their env.
 They share many characteristics of life (unity)
 There is a rich diversity among org’s
Darwin’s voyage with Beagle
Darwin in 1840,
after his return
from the
HMS Beagle in port
20 40
Santa Santa
Cape of
Good Hope
Cape Horn
Natural Selection: A Summary
 Individuals with certain heritable traits survive and reproduce at a
higher rate than other individuals
 If an environment changes over time, natural selection may result in
adaptation to these new conditions and may give rise to new species
 Natural selection increases the match between organisms and their
environment over time
 It is the populations not the individuals that evolve
 If individuals are genetically identical (no inherited variations in the
population), evolution cannot take place.
 A trait favorable in one place or time may be useless or damaging in
other places and time. Thus, in natural selection which traits are
favored depends on where and when the species live and mate.
 Nature selects the traits  natural selection
Cumulative effects of natural selection
 Natural selection over years cause ancestral species to
change and give rise to descendant species
Ex: due to geographical isolation
Ex: 14 species of finches identified by Darwin in Galapagos
islands is an example of speciation due to geographical
(Galapagos islands are volcanic islands in
Pacific ocean close to South America)
Adaptations of finches in Galapagos islands
(a) Cactus-eater
(b) Insect-eater
(c) Seed-eater
Source of heritable variation: Mutations
 Mutations are changes in the DNA sequence of an organism.
 They give rise to new forms of a given gene  alleles
Ex: Gene 1; encoding for protein A
Allele a of gene 1: encoded protein functions with 80% efficiency
Allele b of gene 1: encoded protein functions with 40% efficiency
 Alleles are different forms of a gene
 Mutations may have neutral, harmful
or beneficial effects on the gene and
the encoded product by that gene.
Mutations occur due to;
 Mistakes during copying of DNA in the cell (DNA
replication) before the cell splits into two
 Collisions of DNA with other molecules
 Damage from radiation and chemical agents
Mutations occur randomly
Mutations do not occur when the organism needs them,
They occur randomly at any time and not directed toward a goal
Ex: bacteria accumulate mutations that confers resistance to
By using these antibiotics in an uncontrolled way, the bacteria
having resistance to that antibiotic are selected and survive. The
antibiotic sensitive ones die.
The mutation that confers resistance to bacteria does not
appear when we take the antibiotic, it is already
present in the bacterial population.
Mechanisms of Evolution
 Mutations: raw material on which evolution can work
 Natural selection: organisms best suited to the
environment survive and reproduce better than individuals
less suited to the environment.
 Genetic drift: chance events that cause some individuals
to leave more offspring than others
 Gene flow: introduction of alleles to a population due to
an exchange of alleles between different populations
Genetic Drift
 Chance events that can cause some individuals to leave more
offspring than others
 Genetic drift and natural selection cause random fluctuations
in the genetic make-up of populations over time
 They act together to produce evolutionary change
 However, in small populations the effect of genetic drift can
be a disadvantage for the species
Genetic Drift
• It can cause loss of an allele even in two generations
• It leads to fixation of only one allele in the population that can be
neutral, beneficial, or harmful
Genetic drift in small populations
 In large populations its effect can be overcome by natural
selection and other evolutionary mechanisms.
 It is important to know about genetic drift for preservation
of rare species
African cheetah
Genetic bottleneck
Small population  genetic drift  loss of genetic
variation  fixation of harmful alleles Extinction
of species
A population experiencing such a situation is said to be in
‘genetic bottleneck’.
Ex: African cheetah
Ex: Florida panthers: males have low sperm counts due to a
harmful mutation that is fixed.
30-50 panthers  increased to 100s
Gene Flow
 When individuals move from one population to the other
they may introduce new alleles to the population they
(As if there occurred a mutation in the new population)
Ex: an allele that confers resistance for a pesticide in
mosquito spread over three continents –Asia, Europe and
North America
The mutation is advantageous for the mosquito but it
counteract the effects of natural selection.
Gene Flow
How gene flow counteracts the effects of natural
If populations are isolated from each other natural
selection favors accumulation of mutations and
species isolation.
However, gene flow among isolated populations keep
their genetic make-up similar.
They may remain genetically similar despite the effects
of natural selection.
Evidence for evolution
 Surveys showed that about 50% of adults in our
country do not believe that evolution is at work
and humans evolved from earlier species of
 Evolution has been defined for 150 years and
evidence is very strong.
 For scientists the issue is not whether evolution
has occurred but is how evolution works.
Evidence for evolution
 Darwin could not convince some of other scientists
at his time in natural selection because mechanisms
of inheritance was not known.
Lines of evidence
There are four types of data that document the pattern
of evolution;
 Direct
 Homology
 The fossil record
 Biogeography
The Evolution of Drug-Resistant Bacteria
 The bacterium Staphylococcus aureus is commonly
found on people
 One strain, methicillin-resistant S. aureus (MRSA) is a
dangerous pathogen
 Resistance to penicillin evolved in S. aureus by 1945, two
years after it was first widely used
 Resistance to methicillin evolved in S. aureus by 1961,
two years after it was first widely used
 MRSA strains are now resistant to many
Evidence of evolutionary history: homology
 Evolutionary relationships among organisms can be
determined by their anatomical features.
Ex: bat wing and human arm; remarkable similarity in
limb structure with different function
human cat
Evidence of evolutionary history: homology
 Homology is similarity resulting from common ancestry
 Homologous structures are anatomical resemblances that
represent variations on a structural theme present in a common
Ex: Whale embryos with teeth (disappear in adult)
Ex: Human embryos have gill pouches (develop into ear bones)
Fossil records: Whales evolved from organisms with teeth.
A group of fish  first amphibians : a group of amphibians  first
reptiles: a group of reptiles  first mammals: a group of
mammals  human
They are preserved remains or impressions of formerly
living organisms.
 Document extinction of species
 How descendants of species changed overtime
 How new organisms have evolved from ancestral organisms
 How environments changed over time
(Fossils of whales in Sahara desert; fossils of trees and
tropical marine organisms in Antarctica)
(Manatees and relatives)
Elephas maximus (Asia)
Loxodonta africana (Africa)
Loxodonta cyclotis (Africa)
5.5 2104 0
Millions of years ago
Years ago
In 32 MY, 7 elephant
species became extinct.
Thus, there is no species to
fill in the gap between elephants
and their nearest relatives
99% of species are now extinct!!!
Fossil records have many gaps due to several reasons:
 Organisms decompose very rapidly after death
 May be destroyed by geographical processes
(erosion, heat, pressure)
 Difficult to find
Each year new discoveries fill in these gaps.
Fossil records show five mass extinctions of species.
 Each caused about 50% of species to be lost
 After each mass extinction surviving groups diversified, caused
bursts of evolution
 Each of these bursts in evolution lasted about 10 million years.
Ex: dinosaurs went extinct 65 mya, mammals diversified in size and
ecological role, otherwise human probably would not exist.
 Sixth mass extinction can be the one that is caused by human
Evidence of evolutionary history
 DNA sequence/ protein analyses:
the higher the homology between
the DNA sequence the more closer
the species in evolutionary tree.
 If organisms were not related to
one other by a common ancestor,
there would be no reason to expect
a degree of similarity in DNA and proteins.
Evidence of evolutionary history
 These different sources of information (anatomy and
DNA sequence) are usually the same.
 Independent lines of evidence yield the same result.
Evolutionary tree
Branch point
and snakes
Hawks and
other birds
Evidence for evolution: Biogeography
Biogeography, the scientific study of the
geographic distribution of species, provides evidence
of evolution.
Earth’s continents were formerly united in a single
large continent called Pangaea, but have since
separated by continental drift.
An understanding of continent movement and
modern distribution of species allows us to predict
when and where different groups evolved.
Evidence for evolution: Biogeography
Continental drift
 Earth’s continents move over time.
 South America and Africa move away from each other
Ex: today’s lungfish is found only in Australia, its ancestors lived in
the single continent of earth (Pangaea)
and their fossils are found on all continents
except Antarctica.
Ex: today’s modern horse first evolved in North America, oldest
fossils are found in North America. The land bridge between
North and South America formed 3 mya. Fossils of ancestors in
South America is less than 3 million years old.
Genetic changes within species
 The tremendous variation produced by human
within dogs and ornamental flowers
 Breeding organisms only with certain characteristics
 artificial selection
 Natural selection can produce
similar evolutionary changes
What Is Theoretical About Darwin’s View of Life?
 In science, a theory accounts for many observations
and data and attempts to explain and integrate a
great variety of phenomena
 Darwin’s theory of evolution by natural selection
integrates diverse areas of biological study and
stimulates many new research questions
 Ongoing research adds to our understanding of
Human Evolution
 Human beings are animals;
 Mammals  primates  hominid
 As other animals we have body hair and mammary
 As primates we have;
Flexible shoulder and elbow joints
Five functional fingers and toes
Thumbs that are opposable
Flat nails (not claws)
Brains large in relation to our body size
Who are we? Where do we come from?
 Genetic analyses and fossil discoveries lead to
understanding our evolution
 Chimps and human diverged about 5-7 mya
 Diverged from gorilla about 7-8 mys
 Diverged from the lineage of orangutans about 12-16
DNA analyses results
 The difference between chimp and human DNA is
about 1%.
 In some regions our DNA is closer to that of gorillas.
 In still other regions chimps and gorilla are more
closely related to each other than to human.
We are Apes
 We are not just closely related to APES but we are
Characteristics shared by apes;
 Use of tools
 Capacity for symbolic language
 Sense of self-awareness
HOMINIDS (pr0-human)
 Primates are thought to have originated 80-85 mya
from small mammals (fossils date 56 mya).
 They were eating insects and living in trees.
 Over time they diversified giving rise to hominids.
 Have large brain
 An upright walking posture
 Complex tool making behaviors
First big step
 Tool making and intelligence are secondary changes
in evolutionary sense.
 The first big step in human evolution was a shift
from being quadrupedal (moving on four legs) to
being bipedal (walking upright on two legs).
 It was a change occured long before hominids
evolved large brains.
Standing up
 Standing up freed our hominid hands to eventually
allow for tool use.
 Tool use led to greater success in hunting or
otherwise acquiring meat in the diet.
 A diet rich in meat provided more of the basic
biochemical building blocks needed for brain
 Someone, at some point, learned how to use fire.
Someone started talking. Someone started writing.
First big step
 It is accompanied by skeletal changes; including loss
of opposable toes (the big toe is opposable in all
primates except humans).
 Loss of it on the trees was a disadvange but on the
ground it was an advantage.
 Thus, evolution to upright posture is linked to a
switch from life in the trees to life on the ground.
(Probably occured 8-5 mya)
Earliest known hominids
 Sahelanthropus tchadensis
(6-7 my old skull found in 2002)
 Ardipithecus ramidus (5.8-4.4 mya)
 Australopithecus species
(4.2-3.0 my old)
 Female
 Ardipithecus ramidus
 Found in Etopia in 1992
 The fossil is 4.4 my old
 Female
 Australopithecus afarensis
 Found in 1974 in Etopia
 3.2 my old
 Small skull
 Bipedal
 Evidence for: bipedalism preceeded increase in brain
Earliest known hominids
 The last two might have upright posture;
 the size of brains were relatively small;
 and their skull and teeth were more similar to other
Evolution of genus Homo; Homo habilis
 Oldest homo fossils were found in Africa; date to 2.4 mya
 Homo habilis (1.9-1.6 mya)
Their fossils resemble to those of Australopithecus
In their most recent fossils the face is not pulled forward
and the skull is more rounded.
Homo erectus
 Homo erectus evolved from H. Habilis
(from which sub-species is not known)
 H. erectus or an earlier form had migrated from
Homo fossils
 Have been found in Java, Georgia (central Asia), China
(dating 1.9-1.7 mya)
 H. habilis lived near Indonesian islands 1 my -25.000
years ago.
 H. sapiens live in the same regions from 60.000 years
ago to present.
 There are more species of homo than thought before and
several of them existed in same places and times.
Homo sapiens
 Originated between 400.000 – 130.000 years ago.
 Some of these are lost 30.000 years ago.
 Early species of archaic H. sapiens gave rise to both;
Modern humans
 Neandertals lived from 230.000 to 30.000 ya.
 Modern human fossils;
Oldest fossils date to
130.000 y in Africa
115.000 y in Israel
60.000 y in China
56.000 y in Australia
18.000-13.000 y in America
Origin of human
The two hypothesis;
 Out of Africa hypothesis; human evolved 200.000 ya
in Africa from unknown archaic H. sapiens
Than, spread to the world, completely replacing all of
the H. sapiens populations (H. erectus, Neandertals,
H. floresiensis)
Origin of human
 Multiregional hypothesis; proposed that modern
humans evolved over time from H. erectus located
throughout the world. Regional differences
developed early but gene flow caused them to remain
as a single species.
Origin of human
 DNA analyses results support out of africa
 However, ‘complete replacement’ is questionable.
 DNA analyses show that genes from archaic
populations outside Africa might have contributed to
genetic make-up of modern humans.
Our evolutionary future
 Genetic drift was the likely evolutionary mechanism in
older ages.
 The populations were small and isolated, without gene
 Now that the human populations are large and not
isolated, genetic drift has probably not have a major role.
 Instead, gene flow plays a critical role and may reduce
differences among populations over time.
Our evolutionary future
 Natural selection does not act in the same way as in
older ages but it is still at work
Ex: infectious diseases apply a pressure on
Ex: resistance to malaria increased in frequency so
rapidly that it can be best explained by natural
Effect of human on evolution
 Cut down forests
 Drain wetlands
 Plow grassland
 Add chemicals to air, water, soil
 Kill large predators
 They cause profound changes in env. where species live.
 Species evolve in response to env.
 The changes we make to those env.s alter the course of
evolution in many species.
Effect of human on evolution
 We should understand how we affect evolution.
 Based on current forest breakdown scientists estimate that all the
world’s tropical forests will be cut down in the next 50 years.
 Since over 50% of world’s species live in tropical forests we may
cause sixth mass extinction.
 If that happens, course of evolution
will be altered and history of life on
Earth may change forever.
 Recovery requires millions of years.