What scientific explanation can account for
the diversity of life?
Biodiversity- the degree of
variety of life.
Where do these differences
The differences in these organisms stem from
differences in their DNA (genetic diversity).
Genetic diversity- differences
in DNA among the same
species of a population
resulting in different physical
Ex- why are these puppies all
colored differently even though
they are littermates?
Evolution, or change over time in a population, is
the process by which modern organisms have
descended from ancient organisms.
A scientific theory is a well-supported testable
explanation of phenomena that have occurred in the
Evolution does not explain the origin of life itself.
So how does evolution happen?
J.B. Lamarck: Theory of Acquired
Published 1809 – same year Darwin and Abraham
Lincoln were born.
1st “complete” theory of evolution
Charles Darwin: Theory of Natural Selection
Published in On the Origin of Species in 1859.
Jean-Baptiste Lamarck 1744-1829
Proposed the Theory of Acquired
CharacteristicsBy selective use or disuse of
organs, organisms acquired
(gained) or lost certain traits during
their lifetime. These changes were
then passed on to their offspring.
Over time, this process led to
change in a species.
Lamarck’s Giraffe Example
Known as the “father” of evolution
Proposed that evolution happens by
“natural selection” or survival of the fittest
Born in England (Feb. 12, 1809)
Left England on a ship known as the HMS
Beagle in 1831 for a voyage around the
Made observations on the Galapagos
Darwin was the “first” to “discover” why
evolution happens. He published his ideas
in a book called On the Origin of Species
by Natural Selection in 1859
A group of islands located ~1,000 km
(around 620 miles) west of South America
Islands very close together but had very
different climates and different types of
Darwin studied ground tortoises
, iguanas, and finches
Giant Tortoises of
the Galápagos Islands
Discussed how organisms evolved from
other organisms and how new species
formed from “common ancestors”
Ex- the lion, tiger, panther, bobcat and common
house cat all descended or “came from” a
Ex- Tigers, dogs, horses, and bats share a
common ancestor because they are all
Darwin’s theory of evolution by
1. In nature, there is a struggle for
existence, meaning that there is
competition between each species for
resources such as
food, water, shelter, and space; in the
same species there is competition for
Ex- In predators, such as wolves, the wolf that
has the ability to catch more rabbits will survive
and reproduce more
Ex- In prey, such as rabbits, that rabbits are
faster, better camouflaged, etc. and will survive
Natural selection-Individuals that are
better adapted and more “FIT” will survive
and reproduce more successfully.
aka “Survival of the fittest”
5 points of Darwin’s Theory of
1. There is genetic variation within populations
2. Some variations serve an organism better than
3. More young are produced in each generation
than can survive
4. Those that survive and reproduce must be
those with better variations
5. Over enormous spans of time, small changes
gather and populations change to the point of
forming new species.
So what makes some organisms “better” than others?
An adaptation is a genetic change within a
new species that increases its fitness
Ex- long legs, camouflage, jumping ability, etc
Fitness is defined as an organism’s
chances of survival until it can reproduce
Depends on factors such as
• Mating success
• Avoiding predators
• Finding food
Which one of these
moths would be
considered more “fit”
for this environment?
Influenced by physical traits
Bill Gates, Microsoft CEO
Brad Pitt, Actor
How quickly does evolution happen?
Ideas differ based on the rate of change
Gradualism – evolution occurs slowly but
steadily over time
Darwin and Lamarck believed this
Punctuated Equilibrium – organisms
change rapidly in bursts, followed by time
Proposed by Steven Jay Gould (1941-2002)
But evolution was not Darwin’s
Idea…He just figured out how it
worked (the mechanism)
Evolutionary thought (and Darwin) was
influenced by many individuals
James Hutton (1785): Geologist estimating Earth to
be millions of years old
Thomas Malthus (1798): Economist studying interplay
between population size and available resources
J.B. Lamarck (1809): Proposed a flawed mechanism
for how organisms change.
Agreements and Disputes
The scientific community agrees that…
Species change over time because of heritable
Present-day organisms have descended from
ancestors from the past
Evolution occurs by natural selection
The Earth is 4.6 billion years old
Many scientists disagree about…
The rate at which evolution occurs
The exact ancestral relationships of species
Evidence of Evolution
Can be found in:
geographic distribution of living species
Paleontologists study fossils.
Fossil – any evidence of an organism that is
Can be mineralized pieces of the organism (often
bones or shells), footprints, tunnels from burrowing
Fossils show, beyond any doubt, that life on Earth
has changed over time.
How mammals adapted
to life in the sea – whale
* Pelvis and hind-limbs reduced
* Tail lengthened for swimming
* Jaws modified for feeding on
Dating Fossils & the Earth
Two methods for determining age of
Radiometric dating – gives an approximate
age (in years) by analyzing the presence of
radioactive isotopes in the sample
Eg) Carbon dating measures C-14; often used on
Eg) Dating rocks on Earth has led to our estimate
of the Earth’s age – 4.6 billion years.
Relative dating – requires 2 objects; can only
tell which is older or younger than the other by
comparing their positions in the ground.
Eg) Fossils in deeper strata (rock layers) are older
than those found in strata above it.
In the strata of your laundry hamper…or
Where are the clothes you wore yesterday?
The day before?
And before that?
And before that?
Why are there “gaps” in the fossil record?
Not all organisms fossilize
Natural processes destroy fossils
Conditions are rarely suitable for
fossilization when an organism dies
They are often buried and hard to find
Fossils (blue) will rarely be on the direct
line of descent to present-day species
Which strata is older?
If we found fossils in Layer A and Layer B, which fossils are older?
2) Geographic Distribution of Living
Similar species exist
Beaver, muskrat, cap
ybara, and coypu are
all similar species that
are found in both N.
America and S.
continents were once
3) Homologous Structures
Structures on different
developed from the
same body part
Ex. The flippers on a
from the same body
part as the arms of
Divergence results in homologous structures
Homologous structure- Structures with different
mature forms but develop from the same embryonic
tissue because they have a common evolutionary
Eg) Vertebrate limbs
Whale flippers, frog forelimbs, and your own human arm
most likely evolved from the front flippers of an ancient
The picture above
shows part of the
pectoral girdle and limb
of two flying
vertebrates known as
the bat and the
Which bone of the
to the humerus of the
4. Comparative Anatomy: Vestigial
Vestigial structure (or organ)- Features that have
lost all or most of their original function and are
similar to structures possessed by ancestral
These are remnants of more developed structures that were
present and functional in ancestors.
Important: vestigial structures are not always “useless” – they
often have reduced functions that are not essential for survival
Humans: appendix, coccyx (tail-bone), body hair, wisdom teeth,
muscles that move our ears
Whales and pythons: hind-limb bones
Pigs: toes that do not touch the ground
Wingless birds: vestigial wing bones
Blind, burrowing or cave-dwelling animals: nonfunctioning eyes.
Hind-limb bones in a whale (top)
and python (right).
Vestigial hind-limbs of a snake
Flightless Cormorants (Nannopterum harrisi) live on the Galápagos Islands.
They must have been able to fly at some time in their history,
but now they have only vestigial wings, which when held out to dry in typical
Cormorant style, look tatty and pathetic. These vestigial wings do not help them
when swimming (they move through the water by kicking their powerful feet),
but they are thought to help them to keep balance when hopping between rocks.
New Zealand’s wingless
group of birds – not the
The wings are not quite absent, as the
name implies, but are extremely aborted,
consisting of a rudimentary humerus and
one complete digit.
In early stages of
backbones are very
6. Biochemical Evidence for
Evolution (DNA similarities)
All organisms made of the same basic
molecules (proteins, carbohydrates, lipids,
All organisms based on the same,
universal genetic code.
The more closely related one species is to
another, the more similarities should be
observed in their biochemical makeup
Amino acid sequences of proteins
Evolution of a Cell
One method of
classification of an
animal is comparing
the amino acid
Convergent vs Divergent Evolution
Divergent evolution (aka. speciation)- when
a group from a specific population
accumulates enough changes that it
becomes a new species and is
reproductively isolated (cannot interbreed)
from its ancestors.
A species is a group of organisms that can
breed and produce fertile offspring.
A population is a group of individuals of the
same species that can breed.
Organisms that have recently “diverged”
share many characteristics, but are too
different to interbreed. Organisms that
diverged a long time ago have fewer
characteristics in common.
Homologous structures are produced by
Causes of divergence in species
Mutation as the cause of divergenceSometimes mutations in the population cause changes
in the gene pool resulting in the emergence of new
species but this is rare!
Ex- a bacterial cell mutates into a new species- MRSA vs
Isolation leads to Divergence
Different types of isolation:
1) Geographic isolation – when
populations become physically
separated & unable to reproduce
Such as the storm-blown finches on
Continental movement, sea level
changes, mountain range formation,
new rivers, etc.
Sometimes referred to as reproductive
isolation because two species can’t
physically come together to mate due
to geographical barrier (like the grand
Sources of isolation
2) Behavioral isolation –two populations are capable of
interbreeding but have differences in courtship rituals or
other reproductive strategies that involve behavior.
These meadowlarks have
overlapping ranges but do
not interbreed because they
have different mating songs.
Each population will evolve
independently and slowly
accumulate more differences.
Sources of isolation:
3) Temporal isolation – individuals mate at
different times of the year.
but they do not
mate at the same
time of year!
Eastern Spotted Skunk
(mates late winter)
Western Spotted Skunk
(mates late summer)
Adaptive radiation – When a single species
diverges rapidly into several different
species which all “occupy” different niches.
Niche – an organism’s role in it’s environment
When 2 organisms occupy the same niche,
Darwin noticed adaptive radiation in finches on
the Galapagos Islands.
Ancestral finch species blown over to the
Galapagos Islands from South America
during a hurricane. In a brand new
environment, the finches rapidly adapted
to exploit available food sources.
Answer these questions????
An organism’s job is
called its _______.
How many different
niches do you
The finches of Galapagos
islands were separated
by very little distance.
However, there were
many different species of
finches with different
beak size and shape that
evolved from a common
finch. What can account
for the different species of
A) closeness of islands
B) many predators
C) different available food
D) each island has a
The island of
Tasmania is off the
coast of Australia. It
is home to the
Devils on Tasmania
are very different from
its cousin on the
mainland of Australia.
What can account for
Convergent evolution – process in which
species that are not closely related to each
other independently develop similar traits.
Eg) Butterflies, hawks, and bats all have
NOT due to a common ancestor passing a “wing”
gene to each
Each kind of wing evolved independently,
suggesting that the trait of flight is useful for the
purpose of survival and reproduction.
These wings are considered to be analogous
A result of convergent evolution,
analogous structures look and function
similarly but do not share a common
These structures perform the same function (flight),
but they evolved independently.
Streamlined bodies and various appendages for moving quickly through water…
Yet a shark is a fish…
Penguins are birds…
And dolphins are mammals.
response to the
of a marine life.