Transcript Natural Selection

Classification of Organisms
In 1735 Linnaeus developed the following
hierarchical taxonomic classification
 Kingdom - Animalia
 Phylum - Chordata
 Class - Mammalia
 Order- Primates
 Family - Hominidae
 Genus - Homo
 Species - sapiens
By hierarchical we mean that the highest categories
(Kingdoms) contain many sub-categories, etc.
By taxonomic we me organisms are grouped
together according to the similarity of their organ
structure and function.
You can imagine the classification scheme of life as a
giant “tree of life”.
The trunk would split into five great branches: the
kingdoms of life.
Each great branch would split into dozens of smaller
branches : phyla
Each phyla branch would split into dozens of classes,
and so forth.
At the edges of the tree would be millions of tiny
twigs: species.
So let’s explain the classification chain for humans:
Kingdom – Animalia: means we are not bacteria,
amoebae, plants or fungi (these
are members of the other four
kingdoms)
Phylum – Chordata: means we are among those animals
with spinal columns. Excluded
would be animals like garden
slugs, insects, clams, and coral.
Class-Mammalia: means we are warm blooded, have
hair, give birth to live young, etc.
Excluded would be the other classes
of animals with spinal columns: fish,
amphibians, reptiles, and birds.
Order-Primates: This group includes tarsiers,
monkeys, gibbons, the great apes
including humans.
Family-Hominidae: This would include the great
apes: orangutans, gorillas,
chimpanzees, humans
Genus-Homo: Presently we are the only species in
the genus (big foot?), but 40,000
years ago or so there were beside us:
Homo Neanderthalis, Homo
florensiensis (the “hobbit”), Homo
denosovan, and Homo erectus (?)
Species- sapiens
Now don’t panic. Just be familiar with the kingdoms.
I only wanted to show you how the system works.
Five
Kingdoms of
Life
Classification of Organisms
Kingdom Monera: prokaryotes (no nuclei in the cells)
include bacteria, cyanobacteria (formerly known as bluegreen algae)
The other four kingdoms have cells with a central nucleus
where the genetic material is stored. The nucleus rests
within a fluid called cytoplasm that contains various bodies
(such as mitochondria and vacuoles). The cell is covered
with a cell membrane that controls what chemicals enter
and leave the cell.
The next four kingdoms are eukaryotes (having nuclei)
Kingdom Protista: microorganisms such as
dinofagelata, algae, seaweed, Foraminifera.
Kingdom Fungi: mushrooms, molds, yeast, lichens.
Kingdom Metaphytae (Plantae): mosses, ferns,
trees, flowering plants, salt-marsh grasses.
Kingdom Animalia (Metazoa): jellyfish, corals,
sponges, sea stars, birds, cats, snakes, etc.
Animalia (Jelly fish)
Protist (Foram)
Fungi
(mushroom)
Plantae (Salt-marsh
grass)
Classification by Lifestyle
• Plankton: organisms which float in the water and
•
have no ability to propel themselves against a current
-phytoplankton (photosynthetic autotrophs)
-zooplankton (heterotrophs)
-bacterioplankton (bacteria that float)
Nekton: active swimmers and include marine fish,
reptiles, mammals, birds and others
• Benthon: organisms which live on the bottom
(epifauna) or within the bottom sediments (infauna)
– Some organisms cross from one lifestyle to another (pelagic
early in life and benthonic later)
Charles Darwin’s
Theory of Evolution by Natural Selection
There are really two parts to this idea.
•Evolution is not really a theory but an observation, largely
based on the fossil record, that life changes over time.
•Natural Selection is the process that Darwin theorized
drove evolution. Most biologists believe natural selection is
the dominant process. It works as follows:
•More offspring are produced than can survive to
reproductive age.
•Random variations occur in all organisms. Some of these
variations are inheritable, that is, they can be passed on to
offspring.
•Some inheritable traits are favorable in that they increase the
probability that organisms possessing them will survive.
•Because bearers of favorable traits are more likely to survive,
they are more likely to reproduce and pass on traits. These
traits accumulate in the population; they are selected.
•The physical and biological environment does the
differential selection. Favorable traits are retained because
they contribute to the organism’s success in the environment.
These traits show up more often in succeeding generations if
the environment is constant. If the environment changes,
other traits become more favorable and the organisms with
those other traits preferentially reproduce in that
environment.
How do new traits come about?
•Through mutation: inheritable change in an organism’s genes.
Most mutations are unfavorable, that is they produce unfavorable
traits. Such mutations tend to be eliminated by the environment
or other organisms.
•Mutations occur randomly, but natural selection is not random.
•Natural selection takes huge amounts of time, but there is plenty
of time because the Earth is 4.6 billion years old.
•Evolution by natural selection is the accumulation of these
beneficial inheritable structural and behavioral trains know as
adaptations.
•Evolution is the maintenance of life under changing conditions
by continuous adaptation of successive generations of species to
their environment.
What is a species?
•A species is a group of interbreeding organisms that is
reproductively isolated from all other forms of life.
•Speciation: the process of new species formation.
•Physical isolation of a group of organisms is important in
speciation. Since the population is small, favorable traits may
accumulate rapidly or unfavorable traits may die off to suit a new
environment. Generally the smaller the reproducing population,
the faster the rate of evolutionary change.
•A good example is the one Darwin himself studied: the isolated
Galapagos Islands off the west coast of South America. Here
are the giant Galapagos tortoises found nowhere else. Darwin
theorized that a small population of South American turtles
managed to arrive on the islands where the new environment
selected traits (like giant size) that are different than the South
American traits.
•Divergent evolution: one group radiates into many
different species and lifestyles. Example: wolves, foxes, and
coyotes have a common ancestor that lived millions of years
ago.
•Convergent evolution: similar conditions may result in
coincidentally similar organisms. Example: porpoises are
mammals that originally lived on land and had hair, feet with
claws, external ears, and mammal-like tails. They moved to
the sea and that new environment selected more fish-like
traits.
•Darwin did not know about DNA or genes so he could only
speculate about how new traits form and are passed on.
Evolution
Charles Darwin: “I have called this principle, by which
each slight variation, if useful is preserved, by the term
Natural Selection.” (The Origin of Species, 1859)
Darwin’s theory was based on:
Natural Selection
heritable variation
differential survival
Reproduction
*but he offers no mechanism
Mechanisms for this theory
include:
Neo-Darwinism or
New Synthesis
Is a combination of genetics and Darwinism:
postulates that natural selection is the product of
mutations in DNA (slow and gradual process)
Symbiosis
Close association of two unlike organisms, usually
lasting for a long time.
Example: Cleaner fish follow sharks closely eating
food scraps, dead skin, parasites from the shark’s
mouth and sides. In return they get the shark’s
protection.
Example: Single-celled algae live in the tissues of coral
animals. Both organisms get benefits from this
association which is called mutualism.
Evolutionary Pathways for Organisms
Speciation: is the splitting of a single species, most
commonly brought about by populations becoming
geographically isolated
Divergent evolution: when a single group of
organisms splits into two groups and each group evolves
in increasingly different directions
Convergent evolution: evolutionary change in two or
more unrelated organisms that results in the
independent development of similar adaptations to
similar environmental conditions
GAIA THEORY
James E. Lovelock (1972) and Lynn Margulis
The scientific hypothesis proposes that the whole
Earth behaves like one self-regulating organism
wherein all of the geologic, hydrologic, and biologic
cycles of the planet mutually self-regulate the
conditions on the surface of the Earth.
Gaia Theory
•Feedback from biota to biosphere
•As biota evolve, so does biosphere
“Life and its environment are so closely coupled that evolution
concerns Gaia, not the organisms or the environment can be
taken separately” (Lovelock, 1993)
•Algae and bacteria are key links