Transcript Evolution Basic Concepts for AP Biology ppt.

Descent with Modification
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A basic definition of
evolution is change in
species over time
A more specific definition is:
a change in allele
frequencies in populations
over time
Evolution occurs because
populations vary in the
frequency of heritable traits
that appear from one
generation to the next.
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The body structures of the present-day
Armadillo show its evolutionary
relationship to the Glyptodon.
When one generation
of organisms
reproduces and
creates the next, the
frequencies of the
alleles for the various
genes represented in
the population may be
different from what
they were in the
parent generation.
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Frequencies can change
so much that certain
alleles are lost and/or
others become fixed (all
individuals have the
same allele for that
trait).
Over many generations,
the species can change
so much that it becomes
quite different from the
ancestral species.
Natural selection can create new species.
These Hawaiian honeycreepers all
evolved from a single ancestor, which
arrived on the islands long ago.
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One of the main ways that evolution occurs in
a population is by natural selection.
Natural selection is the differences in survival
and reproduction among individuals in a
population as a result of their interaction with
the environment
NOTE—natural selection
is NOT the only process
by which evolution occurs!
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Some individuals
possess alleles
(genotypes) that
generate traits
(phenotypes) that
enable them to cope
more successfully in
their environment
than other
individuals.
Nature “selects” individuals who have
favorable traits—these are the ones who
survive and reproduce.
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1. Overproduction—
Populations possess an
enormous reproductive
potential—all organisms
produce more offspring
than can possibly survive
and reproduce.
Yet, population sizes
generally remain stable.
Resources are limited,
therefore, there is
competition for survival—
not all individuals will
survive.
Darwin calculated that 2 elephants
would produce a population of 19
million individuals after 750 years if
all offspring survived to reproductive
maturity and fostered their normal
number of offspring.
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Variations among
individuals are
inherited traits.
In every population,
there is variation
among the
individuals.
Some individual traits
are better than others
in a particular
environment.
Within this population of
elephants, there are variations in
their inherited traits. Some
individuals have inherited more
favorable traits.
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Only the most fit
individuals survive in a
particular environment.
Survival of the fittest
occurs because
individuals with traits
best adapted for
survival and
reproduction are able to
outcompete other
individuals for
resources and mates
Certain individuals posses traits that
enable them to survive and
reproduce. Those who can survive,
do so and are able to pass their
favorable traits to their offspring.
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Over time, evolution
occurs as favorable
traits accumulate in the
population.
The best adapted
individuals survive and
leave offspring who
inherit the traits of their
parents.
In turn, the best
adapted of these
offspring leave the most
offspring.
Over time, traits best
adapted for survival and
reproduction and the alleles
that generate them
accumulate in the
population.
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Adaptation is an
outcome of natural
selection. It is the
gradual matching of an
organism to its
environment over time.
Example: The short-nosed echidna of Australia and Tasmania is
well adapted to its diet of ants and termites. It has powerful claws
to break into ant nests and termite mounds, and a long, sticky
tongue to collect its prey. The short-nosed echidna also has spines
to protect itself. It cannot roll up like a hedgehog – instead, when
threatened, it digs quickly downwards to protect its soft
underbelly.
Evolution
in a
Nutshell:
http://www.mh
he.com/biosci/e
sp/2001_gbio/f
older_structure/
ev/m2/s1/evm
2s1_6.htm
In the end,
green beetles
have been
selected against
and brown
beetles have
flourished.
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Microevolution—
describes the details
of how populations of
organisms change
from generation to
generation and how
new species originate.
Gene frequency refers to how frequent a gene or allele is in a population.
The white allele has a frequency of 43% in the mouse population
illustrated here. 13 of the 30 alleles are white.
A change in the gene frequency of a population results in small
evolutionary changes or microevolution.
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Macroevolution—describes patterns of changes in
groups of related species over broad periods of
geologic time . The patterns determine phylogeny
Phylogeny is the evolutionary relationships among
species and groups of species.
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One of the earliest advocates for evolutionary
theory was Jean Baptiste Lamarck (1800s). His
ideas included the following:
1. Use and disuse: describes how body parts
can develop with increased usage, while
unused parts weaken.
This part of Lamarck’s ideas is
true—as you can see with this body
builder.
However, as you will see next, the
rest of Lamarck’s ideas were
incorrect.
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2. Inheritance of acquired characteristics—described
how body features acquired during the lifetime of an
organism could be passed on to offspring. (Is this true?
Can this happen? )
3. Natural transformation of species—described how
organisms produced offspring with changes,
transforming each subsequent generation into a
slightly different form toward some ultimate, higher
order of complexity. (Is this true? Can this happen?)
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Fifty years after Lamarck published his ideas,
Darwin published The Origin of Species by
Means of Natural Selection.
Darwin’s theory that natural selection is the
driving force of evolution has become one of
the most important in biology today.
Later, genetics was incorporated into
evolutionary thinking, creating a new, more
comprehensive view of evolution, now called
the modern synthesis.
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According to
Lamarck, giraffes
evolved long necks
by:
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According to Darwin,
giraffes evolved long
necks by:
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Paleontology is the study of prehistoric life. It
provides fossils that reveal the prehistoric
existence of extinct species. Changes in species
and the formation of new species can be
studied.
Fossil deposits are most commonly found in
sedimentary layers.
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Biogeography uses geography to describe the
distribution of species. This information has revealed
that unrelated species in different regions of the world
look alike when found in similar environments. This
provides strong evidence for the role of natural
selection in evolution.
Emu—Australia
Ostrich—Africa
Rhea—South America
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Embryology studies the development of the
embryo from the zygote to the fetus.
Embryology reveals similar stages in
development (ontogeny)
among related species.
The similarities establish
evolutionary relationships
(phylogeny).
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Comparative anatomy describes two kinds of
structures that contribute to the identification of
evolutionary relationships among species:
Homologous structures and Analogous structures.
Homologous structures are body parts that resemble one another
in different species because they have evolved from a common
ancestor. Because anatomy may be modified for survival in
specific environments, homologous structures may look
different, but will resemble each other in pattern.
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Analogous structures
are body parts that
resemble one another
in different species,
not because they have
evolved from a
common ancestor, but
because they evolved
independently as
adaptations to their
environments.
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Molecular biology examines the nucleotide and
amino acid sequences of DNA and proteins
from different species.
Closely related species
share higher percentages
of sequences than species
distantly related.
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Stabilizing Selection
Directional Selection
Disruptive Selection (or diversifying selection)
Sexual Selection
Artificial Selection
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Stabilizing selection eliminates individuals that have
extreme or unusual traits.
Under this condition, individuals with the most
common trait are the best adapted, while individuals
who differ from the common form are poorly adapted.
As a result, stabilizing selection maintains the existing
population frequencies
of common traits while
selecting against all
other trait variations.
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Directional selection favors traits that are at one
extreme of a range of traits. Traits at the opposite
extreme are selected against.
If directional selection continues for many generations,
favored traits become more and more extreme, leading
to distinct changes in the allele
frequencies of the population.
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Disruptive Selection occurs when the
environment favors extreme or unusual traits,
while selecting against the common traits.
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Sexual selection is the differential mating of males
(sometimes females) in a population.
Since females usually make a greater energy
investment into producing offspring than males, they
can increase their fitness by increasing the quality of
their offspring by choosing superior males.
Males, on the other hand, contribute little energy to the
production of offspring and
thus increase their fitness by
maximizing the quantity of
offspring produced.
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Traits that allow males to increase their mating
frequency have a selective advantage and, as a
result, increase in frequency in the population.
Male competition—leads to
contests of strength that award
mating opportunities to the
strongest males.
Female choice—leads to traits
or behaviors in males that are
attractive to females.
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Artificial selection is a form of directional
selection carried out by humans when they
sow seeds or breed animals that possess
desirable traits. Since it is carried out by
humans, it is not “natural” selection, but is
given here for comparison.