Transcript Evolution 2

Examples of Selection in Action
Antibiotic resistance in bacteria: the widespread
use of antibiotics has led to the evolution of strains
of bacteria that are resistant to many of our
antibiotics.
What is tuberculosis?
Tuberculosis (TB) is an infectious disease caused by the
bacteria Mycobacterium tuberculosis.
The bacterium has a thick waxy
coat, allowing it to lie dormant
in the body for many years.
The TB bacteria attack the
respiratory system, causing
coughing, fever and fatigue.
How do you think TB is
transmitted?
TB facts and figures: 2004
Region
Incidence
Prevalence Mortality
(thousands) (thousands) (thousands)
Africa
2,573
3,741
587
Americas
363
466
52
Eastern
Mediterranean
645
1,090
142
Europe
445
575
69
South-East Asia
2,967
4,965
535
Western Pacific
1,925
3,765
307
Total
8,918
14,602
1,692
TB is one of the world’s most serious diseases.
Healthy people can fight TB
Only 10% of healthy people exposed to TB develop the
active disease. People most at risk are those who:
 have a weakened immune system
 live in squalid or overcrowded conditions.
1,000 people exposed to TB
900 uninfected
100 infected
90 dormant TB
10 active TB
7 survive
3 die
US TB deaths (1990–2004)
TB deaths in the US
Infectious diseases usually decline as living conditions and
standards of healthcare improve over time.
30,000
25,000
20,000
15,000
10,000
50,000
0
year
Deaths from TB infections
What is different about TB death rates in Africa compared
with the rest of the world? They are increasing.
deaths (100,000s)
14
12
rest of world
10
8
6
4
Africa
2
0
1995 1996 1997 1998 1999 2000 2001 2002 2003 2004
year
How is TB treated?
TB is treated with a 6-month
course of antibiotics. Three
or four different antibiotics
are taken daily to fight the
many drug-resistant strains.
Why does the treatment
last for 6 months?
To ensure that dormant
bacteria are also killed.
The BCG vaccine for TB was developed in 1921. It is 50-80%
effective, but is too expensive for use by developing countries
to vaccinate whole populations.
Directly Observed Treatments System
To lower the costs of treating TB in developing countries,
healthcare workers are paid to make sure patients swallow
every pill they are prescribed. This is the Directly Observed
Treatments System (DOTS).
DOTS helps prevent drugresistant TB from
increasing, and limits the
number of patients who
relapse and need more
expensive treatments.
Drug resistance can evolve in just three months but new
antibiotics can take years to develop.
Warfarin is a rat poison which kills rats by
stopping blood clotting. Many rats are now
resistant to warfarin and have developed an
enzyme that still allows their blood to clot
even in the presence of the drug!
Copper-tolerant plants have evolved in
areas where the land has been mined for
copper. Copper is a metabolic poison and
usually kills plants, but some have evolved a
mechanism to transport the copper out of their
cells.
Practice
Find an example of a variation in a real
organism, something that is distinctive.
Describe how this variation is beneficial to the
success of this organism in it’s particular
environment.
Hypothetically alter the organism’s environment
enough to make this variation no longer
beneficial, but detrimental to the organism’s
success. Describe this change and its effects.
How do we know natural selection can change a
population?
– we can recreate a similar process
Artificial Selection
For thousands of years, humans have practiced
selective breeding, by crossing animals or plants
with desired characteristics in the hope that the
offspring will inherit the best features.
Artificial selection and natural selection have the
same end in mind: passing on favorable
characteristics.
However, artificial selection is human’s way of
speeding up the process.
Artificial selection provides a model
that helps us understand natural
selection.
High milk-yielding cows are mated
with fast-growing bulls to produce
calves that grow quickly and
produce a lot of milk.
Pedigree dogs have been bred
for certain desirable
features.
Adaptation
•Evolutionary process whereby a population
becomes better suited to its habitat
•Takes place over many generations.
Adaptation
Structural adaptations
are those that create a
morphological (physical)
difference
(ex. A mountain goat’s
feet have developed for
mountainous terrains, or
the shape of legs in
different animals to run
faster or jump higher.)
Camouflage
–
–
–
–
Cryptic coloration (blending into environment)
Countershading (dark on top, light on belly region)
Warning coloration (bright colors)
Mimicry (one organism looks like another, more
dangerous, one
Adaptation
•Evolutionary process whereby a population
becomes better suited to its habitat
•Takes place over many generations.
MISCONCEPTIONS
• Changes in the body
What about behavior?
• Changes in the body to fit a location
Do individuals adapt?
Are changes happening because
they are needed?
Misconception: “Natural selection
involves organisms ‘trying’ to
adapt.”
• Natural selection leads to adaptation, but
the process doesn’t involve “trying.”
• Natural selection involves genetic variation
and selection among variants present in a
population.
• Either an individual has genes that are good
enough to survive and reproduce, or it does
not—but it can’t get the right genes by
“trying.”
Misconception: “Natural selection
gives organisms what they ‘need.’ ”
• Natural selection has no intentions or
senses; it cannot sense what a species
“needs.”
• If a population happens to have the genetic
variation that allows some individuals to
survive a particular challenge better than
others, then those individuals will have
more offspring in the next generation, and
the population will evolve.
Different types of environment
There are three major types of environment. What are they?
land
freshwater
marine
How do organisms survive in such different environments?
What is adaptation?
All organisms are
adapted to life in
general, such as
having legs for
walking, wings for
flying or leaves for
photosynthesizing.
These are general
adaptations.
Organisms also have specific adaptations. These are
special features or behaviors that have evolved to make an
organism particularly suited to its environmental niche.
A shark’s general adaptations
What are a shark’s general adaptations to life in an aquatic
environment?
streamlined shape
to reduce friction
when moving
through water
fins provide
stability, power
and control
gills have a large
surface area so
that oxygen can be
extracted from the
surrounding water
A shark’s specific adaptations
What are a shark’s specific adaptations to life as an aquatic
predator?
specialized sense organs can
detect the sound, movement and
electrical fields of other organisms
highly sensitive
sense of smell that
can detect drops of
blood from miles
away
lots of very sharp
teeth that are
constantly replaced
silver coloring
underneath acts as
camouflage
The importance of adaptation
Why is it important that organisms are adapted to their
environment?
The better adapted an
organism is to its habitat, the
more successful it will be
when competing for
resources such as food and
mates.
This increases the organism’s
chance of survival and so
increases its chance of
reproducing and passing on
its genes.
How is a polar bear adapted?
How is a polar bear adapted to its extremely cold climate?
white greasy fur repels water and acts as camouflage
thick fur and
body fat insulate
from the cold
large, wide feet
spread the body’s
weight and act as
good paddles and
snow shoes
More polar bears adaptations
Other adaptations that polar bears have evolved to cope
with conditions in the harsh polar environment include:
small ears and small body
surface area to volume
ratio reduces heat loss
eyes have brown irises to
reduce the glare from the
Sun’s reflection
black skin is a good
absorber of heat
How is a camel adapted?
How is a camel adapted to life in a very hot, dry climate?
fat is stored in the hump to reduce overheating
little water is lost
through sweating
or urination
long, thin legs help
to increase body
surface area and
increase heat loss
wide feet spread
out body weight
on shifting sand
More camel adaptations
What other adaptations have camels evolved to cope with
the harsh desert environment?
long eyelashes and
furry ears prevent sand
and dust from getting in
nostrils can be closed
for protection during
sandstorms
very varied diet, ranging
from grass and bark to
thorns and bones.
Other Adaptations
Biochemical adaptations are those that help to regulate a function of
the body.
Examples:
•amount of melanin produced in the skin serves as a protection
against UV radiation
•production of a special fat that bears use as food during hibernation
Kangaroo rat: adapted to desert life. Conserve
water in their bodies—don’t sweat, and only hunt
at night.
Their bodies are so good at conserving water they
don’t even need to drink!
Behavioral Adaptations
In simple animals, behavior is governed by instinct
(pre-programmed by an animal’s genes)
In more complex animals, instinctive behavior is
often modified by learning.
Many forms of behavior help animals to survive .
Behavioral Adaptations
– Hibernation, which enables animals to survive cold and
food shortages in winter
– Estivation (burrowing in the cool mud) which allows
animals to survive drought and heat in summer
– Group defense is common in herding mammals, which
sometimes form a protective ring around their young
Behavioral Adaptations
– Individual defensive behavior is often based on
threatening gestures that make an animal look
larger or more dangerous than it actually is.
Some animals also “play dead”.
What is species?
Species: a group of individuals that look
similar and whose members are capable of
producing fertile offspring in the natural
environment