Transcript Mechanisms of Evolution - Bio-Guru

Theory of Evolution
Chapter 15
The Old Testament
Traditional Christian beliefs
state that all organisms resulted from the
direct actions of a creator
1.Each organism has a specific role to play
2.Each was individually created by God
3.Each organism is such a perfect fit in its environment
because it was “hand-crafted” for that environment.
4.The earth is about 6,000 years old
5.The universe is about 13,000 years old
Cuvier (1769-1832)
1. founder of paleontology (studied fossils –
anatomist)
2. observed that different strata of
sedimentary layers contained different fossils.
3. catastrophism--explained changes in
animal world in terms of catastrophes that had
destroyed whole populations of living things in
prehistoric times (floods etc.)
Hutton (1726-1797) and Lyell (1797-1875)
both were influential geologists
Lyell
a. Theory of uniformitarianism small forces acting over
long periods
of time can result in major changes e.g.
destruction of mountains.
b. great champion of Hutton's work
c. historical and physical continuity of nature
d. Principles of Geology (1830)--greatly influenced Darwin
even
though he himself did not admit biological
evolution
A COMBINATION OF LYELL’S AND
HUTTON’S IDEAS IS EMPLOYED TODAY
Lamarck (1744-1829)
1. Believed that life appears from inanimate
matter by spontaneous generation, and
becomes more complex over time
2. changing environment alters the needs of
the organisms
3. use and disuse alter morphology and is
transmited to subsequent generations
(inheritance of acquired characteristics)
4. Believed the earth was very old
Charles Darwin (1809-1882)
Voyage of the H. M. S. Beagle (1831-1836)
Made observations in Galapagos Islands and
South America.
So What is Natural Selection?
What Darwin inferred from his observations
1. Overproduction of offspring: When there are more
organisms than an environment’s carrying capacity…
2. Struggle for existence: there will be a struggle for
survival a.k.a COMPETITION
3. Genetic Variation: The organisms that possess a
variation that will help them in this struggle, will
survive to reproduce.
4. Differential survival and reproduction: These
favorable traits will be passed on to their
offspring, giving them the same benefit.
Summing it up
In the end, only those members of the
population that are best adapted to their
environment will be successful.
THIS WAS HIS THEORY OF NATURAL
SELECTION
http://www.pbs.org/wgbh/evolution/library/11/2/e_s_4.html
Lamarck versus Darwin / Wallace
Artificial Selection
• Animal husbandry
• Pet breeding
Human beings select desired traits
Sexual Selection
• A form of natural selection where
individuals with certain inherited traits are
more likely to finds mates.
• Sexual selection causes sexual
dimorphism, where there are clear
differences between the two sexes (Like in
human males and females)
Intrasexual Selection –
Individuals of the same
sex compete actively and
sometimes aggressively
for a mate from the
opposite sex. Usually
males display this
behavior.
Intersexual Selection – Individual selects a mate
based on certain physical characteristics such as
showy feathers, muscles, etc. Females usually
follow this route.
Evidence of Evolution
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Fossil Evidence
Anatomical Homologies
Embryological Homologies
Molecular Homologies
Vestigial Organs
Fossil Record
• Sedimentary rocks are the richest source
of fossils
• As a result of these sedimentation periods,
sedimentary rocks form strata
• The deeper the stratum, the older and
simple the organisms
• The higher the stratum, the newer and
more complex the organisms.
Anatomical Homologies
Homologous structures indicate evolutionary ties
Analogy vs. Homology
• Structures that are similar due to
evolutionary origin, such as the forearm
bones of humans, birds, porpoises, and
elephants, are called homologous.
• Structures that evolve separately to
perform a similar function are analogous.
The wings of birds, bats, and insects, for
example, have different embryological
origins but are all designed for flight.
The bones in the three flying animals (not the insect) are homologous, but
the wing structures of all 4 flying animals are analogous
Embryological Homologies
Molecular Homologies
• All life has DNA, RNA and the genetic
code is universal
• So all animals could have descended from
a common ancestor
• Even animals as dissimilar as bacteria and
humans, share common genes inherited
from a distant ancestor.
Vestigial Organs
Adenoids The adenoids are tonsil-like
Tonsils
tissues that are located in the back of
the nose, next to the opening of the
eustachian tube.
Coccyx (tail bone)
Nictitating membrane of eye
Thymus
Appendix
Wisdom teeth
Nipples on males
Parathyroid
Nodes on ears "Darwin's points"
Ear muscles for wiggling
Pineal gland The pineal gland is a tiny
structure located at the base of the brain.
Its principal hormone is melatonin, which
regulates our day and night cycles
Body hair
Fossil Record (basically anatomical homology)
• Transitional fossils
that link the past with
the present
Approximately 50 million years ago, this wolf-size
pakicetid—an ancestor of the whale—lived on land but
may have waded into streams to feed on fish.
Read article on origin of whales
• When a population diverges from an
original population and fills many parts of a
new environment, it is called adaptive
radiation.
• Coevolution – when one species evolves,
the other species that depends on it must
also evolve to survive.
Adaptive
Radiation
Population Genetics and
Speciation
Chapter 16
• A population is a group of individuals in a
certain time and place that belong to the
same species – that is: they can interbreed
and produce viable offspring
• A Gene Pool is the total number of genes
within a population at a particular time and
place.
What causes variations?
• Mutations in an original gene will give rise to
new alleles.
• Alleles will create the variations in a population
that Darwin talked about
• Some alleles will help an organism, others will
harm it
• The alleles that contribute to the survival of a
species in a particular environment, will be
passed on
Gene Pool
• All the alleles in a population are
collectively called the gene pool of that
population
Get Out! The Pool is Closed!
• The Amish for example – the
only variations in the
population arise from
independent assortment and
crossing over during meiosis
and random fertilization within
the community
• No external agents –
immigration, for example
Gene Flow
• When alleles are introduced in or removed
from a population it is called gene flow.
This can happen due to:
• Immigration
• Emigration
Types of Natural Selection
Speciation
• Speciation – the formation of a new species
- Geographical isolation – when some
members of a population become separated from
the main population and eventually accumulated
enough mutations to become a separate species.
-Reproductive isolation – when 2 individuals
can no longer reproduce together, they become
separate species.
Allopatric Speciation
Allopatric speciation of squirrels in the Grand Canyon (see Campbell fig. 24.7, p. 451).
The canyon is a barrier to dispersal by small mammals, and as a consequence the
isolated populations can diverge.
First geographic isolation...
•Unless populations are geographically isolated they will continue to interbreed
...then genetic isolation
•Populations diverge to the point where they no longer interbreed
•This may be due to adaptation to different environments, or genetic drift
Gradualism vs. Punctuated Equilibrium
THE END