or biologic succession
or biologic succession
October 1, 2013
Earth System History
An introduction to evolution and the
For something completely different…
Evolution and the
• Introduction to concepts of evolution and the
• Natural selection
• Understanding life’s pathway
• Life history is not “predictable”
• Life history is not necessarily “progressive”
Fossils and evolution
Principle of fossil succession
(or biologic succession)
William Smith (late 1700's) certain rock units could be
identified by the assemblages of fossils they contained.
Led to the "Principle of biologic succession"
(or fossil succession):
“where present, fossils occur in a consistent vertical order
in sedimentary rocks all over the world.”
This SET THE STAGE for exploring BIOLOGICAL
• Fossil species appear and disappear
throughout the stratigraphic record.
• The Geologic Time Scale was
originally based on these fossil
appearances and disappearances.
• Each of the Geologic Eras ends with
a mass extinction.
• Period boundaries coincide with
smaller extinction events, followed by
appearances of new species.
Geologists interpret fossil succession to be the result
of evolution - the natural appearance and
disappearance of species through time.
What could bring about biological changes under natural
In any population, there will be individuals that are slightly more
tolerant of changes in the limiting factors of the environment
(temperature, salinity, water depth, amount of food, etc.).
One of the greatest
thinkers of all time.
Chuck D. was to
biology what Newton
was to physics!
When environmental conditions change, bringing individual
organisms near their limits of tolerance, there will always be
a few which are at least slightly more tolerant or BETTER
ADAPTED than the population as a whole.
The BETTER ADAPTED individuals will survive to reproduce.
This passes along favorable traits to their offspring.
The concept is familiar to us.
Think about SELECTION. Breeds of dogs and cats. Strains
of Wheat and Corn. Selection by Breeding for the most
THE SAME THING HAPPENS IN NATURE OVER GEOLOGIC
Less-well-adapted individuals die off
individuals live on to reproduce.
Favorable traits will become dominant
in the population.
There will therefore be a shift in the
characteristics of the population.
“I have called this principle, by
which each slight variation, if
useful, is preserved, by the term
from The Origin of Species
"selects" the best
hence the term “Natural
In his time, Darwin and
others did not know HOW
traits were passed from
ancestor to descendent
Yet, since the concept of Natural Selection is a
scientific one, that is, it is TESTABLE, it made
There is a mechanism for biological inheritance
This mechanism has built-in capacity for
change with time
The mechanism must be common to all life
forms on Earth
The mechanism must be independently
verifiable (e.g. with the fossil record).
5. New species must be arising now, and others are
• Evolution is a theory about the
“origin of life”
• NOPE. Evolution deals mainly
with how life changed AFTER its
• However life started, it changed
over time. It branched out. Life
• Evolution is like a climb up a ladder of
progress; organisms are always
• NOPE. Life that survives to reproduce
is life that’s successful.
• No organism has to be perfect! Many
life forms have changed little over time
(sharks, mosses, fungi, possums etc.).
They are not “advancing” or
• Others changed a lot, but that doesn’t
mean they’re getting better!
• Evolution means that life
changed “by chance”
• NOPE. Natural selection is not
random. Random mutations are
• Individuals that survive and
reproduce better in their
environment will have more
offspring displaying the same
• Natural selection involves
organisms “trying to adapt”
• NOPE. Natural selection LEADS
to adaptation, but the process
isn’t about “trying”.
• Genetic variation and selection is
a population is key. You can’t
get the right genes by “trying”
• Natural selection gives
organisms “What they need.”
• NOPE. Natural selection has no
means, senses or intentions.
• If a population happens to have
the genetic variation that allows
some to survive more than
others, their offspring will carry
• Evolution is “just a theory”.
• YES!, But you need to
understand that A Theory is a
very powerful thing. It means:
“In science, a well-substantiated
explanation of some aspect of
the natural world.”
• It’s not a “guess” or a “hunch”.
• Evolution is a “theory in crisis”
• NOPE. Scientists do not debate
WHETHER evolution happens,
but argue over HOW it takes
• The theory of evolution is on
firmer ground than that of many
• Gaps in the fossil record disprove
• NOPE. Evolutionary biologists
do not expect ALL life will get
• Scientists have nevertheless
found MANY transitional forms in
the fossil record (as we will
A few basic terms
Population - a group of interbreeding organisms.
Gene pool - the sum of all of the genetic components
in a population.
Species - The fundamental unit of biological
classification. A group of individuals that are
similar in structure, function, and development, with
the potential to interbreed and produce fertile
offspring. Reproductive barriers between
species prevent interbreeding.
Closely related (but different) species, such as the
horse and the donkey CAN interbreed, but do not
produce FERTILE offspring (mule).
How do organisms pass along favorable
…the parts of a ladder
Watson and Crick discovered the structure of the DNA
molecule in 1953!! This is a very recent science. It is
equivalent, at the very least, to any of the
other great scientific achievements, EVER.
Genetics is the branch of biology that deals with the
study of heredity or inheritance. Darwin did not
know about this, but now we do!
Within the nucleus of each of our cells are chromosomes. In a
human cell there are 23 pairs of chromosomes. (One of these
pairs determines the sex.) Chromosomes consist of long DNA
molecules, highly folded and coiled and combined with a variety
of protein molecules. DNA stands for deoxyribonucleic acid.
The general form of the DNA molecule is described as a "double
helix", which resembles a twisted ladder.
The long part of the
ladder is made of
phosphate and sugar
compounds, and the
rungs on the ladder are
made of nitrogenous
thymine, guanine, and
The part of the DNA molecule responsible for the
transmission of inheritable traits is called a
Chromosomes are composed of genes.
There are approximately 100,000 genes in a
human cell, only a small number of which have
been identified and roughly located on the
DNA carries chemically coded information from
generation to generation, providing instructions
for growth, development, and functioning.
Sexual reproduction = new combinations of
chromosomes. One member of each pair of
chromosomes is inherited from each parent.
This sexual genetic recombination leads
to variability within species of plants,
animals and fungi.
Here is the complete set of human chromosomes. One member
of each pair comes from each parent. Chr#23 determines sex.
Variability of a
Genetic mutations produce alterations in genes and
Mutations are simply chemical changes to the DNA
molecule. They are not necessarily bad!!!
Mutations can be caused by a chemical substance, or
by exposure to radiation (which includes cosmic
radiation and ultraviolet light).
Mutations produce much of the variability on which
natural selection operates.
Variability is the raw material for natural selection.
Low variability “mono culture”
High variability “multi culture”
Chickens and bird flu
Low variability “mono culture”
High variability “multi culture”
The morphology (shape, body plan) of plants and animals reflects
the way that they live. Specialized features of organisms which allow
them to perform useful functions are called adaptations. Morphology
can be examined in terms of the functions it performs - "functional
morphology". When studying the form and function of
morphological features, two categories can be considered:
Homology - body parts with similar origin,
history and structure, without reference to
function. (Homologous body parts.) Similar
body plans suggest common origins.
Analogy - body parts with similar function,
without regard to origin. (Analogous body
parts.) Similar functions but different
Example of homology:
Human and other nonaquatic embryos exhibit gill slits even
though they never breathe through gills. These slits are found in the
embryos of all vertebrates because they share as common
ancestors the fish in which these structures first evolved.
Human embryos also exhibit by the fourth week of development a
well-defined tail, which reaches maximum length when the embryo is
six weeks old.
Similar embryonic tails are found in other mammals, such as dogs,
horses, and monkeys; in humans, however, the tail eventually
shortens, persisting only as a rudiment in the adult coccyx (the tailbone!).
Embryonic rudiments that never fully develop, such as the gill slits
in humans, are common in all sorts of animals.
Some, however, like the tail rudiment in humans, persist as adult
vestiges reflecting evolutionary ancestry.
The most familiar rudimentary organ in humans is the vermiform
appendix. This wormlike structure attaches to a short section of
intestine called the cecum, which is located at the point where the
large and small intestines join.
The human vermiform appendix is a functionless vestige of a fully
developed organ present in other mammals, such as the rabbit and
other herbivores, where a large cecum and appendix store vegetable
cellulose to enable its digestion with the help of bacteria.
Vestiges are instances of imperfections that
argue against creation by design but are
fully understandable as a result of evolution.
1. Human appendix useless yet in other mammals,
including primates, it is necessary to aid in
digestion of high cellulose diet
2. Human external ear muscles still present but
Humans have tailbones
occasionally have tails
4. Human wisdom teeth vestigial compared to other
5. Some snakes have skeletal limbs
6. Cave dwelling crayfish have eyestalks yet no eyes
7. Sometimes vestigial organs may be adapted for new
uses, e.g. penguin wings can't be used for flight
yet adapted for swimming
NEXT TIME: Midterm
after that, more about evolution
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