Download Chapter 5 Evolution Notes

EVOLUTION is change over time
Macroevolution –long-term large-scale evolutionary
changes among species.
Chemical Evolution ---Lasted about 1 billion years
 Earth formed 4.6 billion years ago
 Primitive atmosphere contained CO2, N2, and H2O. Trace
amounts of CH4, NH3 and H2S.
 Energy from electrical discharges, radioactivity, solar
radiation, and heat from earth combined to form first
organic molecules
Biological Evolution ---3.7 billion years
 1st organisms were heterotrophs who ate all the
organism compounds, leading nature to select for those
organisms which could photosynthesize their own food-Prokaryotic cells
Example: Cynanobacteria
 Photosynthesis removed CO2 from air and led to oxygen
build up and the presence of ozone layer, protecting
earth from UV radiation—Oxygen revolution
 Eukaryotic Cell, which were heterotrophic and could
reproduce sexually, leading to genetic diversity
Macroevolution includes all of the following:
 Genetic persistence –Common DNA present in all cells
today indicates common ancestor to all cells
 Genetic divergence –long-term changes in species giving
diversity of life
 Genetic losses –background extinction is steady loss and
mass extinction of lineages.
Evidence for Macroevolution
 Fossils
 Comparative anatomy—homologous parts
 Comparative embryology
 Comparative biochemistry
MICROEVOLUTION –Changes in gene pool of a
population over time
 Changes in the gene pool (sum total of all genes in a
population)of a population overtime
 Source of new alleles is by
o Mutations in DNA of gametes
 Random changes in DNA due to X-rays,
mutagenic chemicals, radioactivity
 Random mistakes made in DNA
o Recombination during meiosis
NATURAL SELECTION –environmental conditions select
those organisms that have favorable variations allowing them
to survive and reproduce more offspring than those without
the variation.
Called “differential reproduction”
VARIATION
 Raw materials upon which natural selection acts
 A difference in some characteristic within a population
 May aide in surviving long enough in an environment to
reproduce and pass on their genes to next generation.
 Color of fur in housecats
 Length of claws
 Number and size of teeth
ADAPTATION
 A heritable trait that helps the population to survive and
reproduce better under current conditions
 Products of evolution by natural selection
 Needles on pine tree
 Binocular vision
 Opposable thumb
TYPES OF ADAPATIONS
 Structural Adaptations –those involving structure or
anatomy
o Shape of tooth
o Hoof of horse
o Snout of pig

Physiological Adaptations –functioning parts of
organisms
o Venom in snakes
o Enzymes in stomach
o Brain synapses
o Pheromones

Behavioral Adaptations
o Squirrels store nuts for winter
o Plant stems grow toward light
o Migration of animals in winter/summer
Environmental Changes challenge organisms to:
 Adapt to the new conditions
 Migrate to an area which is more favorable
 Become extinct
Three Types of Natural Selection

Stabilizing –eliminates the outliers of group and all
organisms become more alike “It pays to be average.”

Diversifying –environmental conditions favor individuals
at both extremes “It doesn’t pay to be normal.”

Directional –changing environment causes shift in favor
of one direction “It pays to be different”
Limits to Adaptation
 Changes in environment can only work on variations that
are present in gene pool

Adaptations are compromises –sickle cell anemia

Population’s ability to adapt is limited by its reproductive
capacity.

Populations that reproduce quickly can often adapt
quickly

Populations that reproduce slowly take a long time to
adapt by natural selection

For a new favorable trait to predominate, most of an
existing population would have to die prematurely

Survival of the fittest means those organisms that leave
the most descendants
SPECIES –A group of organisms that can interbreed and
produce fertile offspring
 Horse & Donkey mate to produce Mule which is sterile
 Tigers & Lions mate to produce Ligers.
SPECIATION –The development of a new species through
evolution.
 Allopatric speciation is most common:
 Geographic isolation –some physical feature separates
the population so they can’t interbreed.
o Landslide
o Flood
o Road
 Reproductive Isolation –When the sperm of one species
cannot fertilize the eggs of another species or the
chromosomes are so different that the embryo cannot
develop.
 Sympatric speciation –less common
 Two species live closely together but cannot interbreed
due to a mutation or subtle changes in behavior
DIVERGENT EVOLUTION –when one species evolves into
two or more species with different characteristics
 Darwin’s Finches
 Galapagos Tortoises
 Dog
 Pine trees
CONVERGENT EVOLUTION –species not closely related
evolve similar traits.
 Usually due to similar roles in similar environments.
 Dolphin—mammal with lungs
 Sea Bass –fish with gills
COEVOLUTION –species evolve depending on the
interactions with other members of their ecosystem
 Predator & Prey—Predator hunts and eats the prey
o Prey develops faster run so predators that can run
faster eat more, live longer, reproduce and pass on
these genes.
o Predator has better eyesight to see motion better, so
prey runs faster, better camouflaged,
EXTINCTION –a species cannot adapt to environmental
conditions and disappear
 Background Extinction Rate –normal loss of species over
time
 Mass Extinction –significant rise in extinction rates above
the background level
o Usually 25-70% of all species lost
o Two mass extinctions and three mass depletions
ADAPTIVE RADIATION –a variety of new species arise
through divergent evolution in new habitats
 Takes one to ten million years to recover
 Ancestral form must reach the new environment
 Ancestral form must have basic adaptations suited to
new environment
 New environment must have no competition
o After mass extinctions, adaptive radiation of mammals
and insects occurred
TWO THEORIES ON RATE OF EVOLUTION

GRADUALISM –evolution occurs at a slow but steady
pace

PUCTUATED EQUILIBRIUM –little or no evolution
occurs while environment is stable, but when a large
change occurs in the environment, many species become
extinct and other rapidly evolve to fill the empty habitats.
BIODIVERSITY = SPECIATION – EXTINCTION
o Humans causing premature extinction above the
background level
o Predictions of extinction of half the present species on
Earth by end of this century
Humans have changed ecosystems to cause some of
the following problems:
 Simplifying ecosystems –monocultures
 Strengthening populations of pest species by producing
genetic resistance
 Eliminating predators
 Introducing new species –cloning
 Overharvesting resources
 Interfering with chemical cycles in ecosystems.
FUTURE OF EVOLUTION
 Artificial Selection instead of natural selection
 Selective Breeding—specific traits
 Cross breeding –takes a long time to develop desired
traits
 Genetic engineering –recombining genes from different
organisms to give new traits that would never appear in
nature
 Genetically Modified Organisms or “transgenic” –result of
gene splicing
o Takes have the time as cross breeding
o Cloning produces genetically identical individual
o Biopharming –genetically engineered animals are
biofactories to produce drugs
 Genetic Engineering raises ethical, moral, legal, and
environmental issues
 Success is 1%
 Questions
 Who benefits
 Who should be notified
 What happens when things turn out harmful
 Who should pay
 Should we use the precautionary principle
 Who gets to decide