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Natural Selection
•! Levels of Analysis in
Ethology
–! Proximate
–! Ultimate (Evolutionary)
Tinbergen
•! Natural Selection
–! Darwin
–! Natural Selection
–! Adaptation/Functionality
Darwin
Levels of Analysis in Ethology
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Example: Why do male monkeys fight?
Niko Tinbergen 1963 “On Aims and Methods in Ethology”
Not mutually exclusive
Answer questions about WHY behaviors occur
Four levels of analysis
–! Proximate Mechanisms
•! Causation
•! Development (“Ontogeny”)
–! Ultimate (Evolutionary) Mechanisms
•! Phylogeny
•! Function
Causation
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Sensory systems
Signals
Neurobiology
Hormones
Motivation
Pheromones
Social cues
Herring gulls
Development
“Ontogeny” means development
•!
•! Age and Experience
–! Physical/mental change and growth
–! Learning is a change in an animal's
behavior in a particular situation
attributable to its previous experience of
the situation
Development
Harlowe’s studies on rhesus social development
Reared in cage alone
Reared in cage with other monkeys
Phylogeny
•! Evolutionary history and
relations to other
species
•! How does the behavior
compare with similar
behavior in related
species?
•! How might the behavior
have arisen through the
process of past
evolution?
Function
•! Did the behavior evolve?
•! Why did the behavior evolve?
•! Does the behavior impact on the animal's
chances of survival and reproduction?
•! Better: how did the trait impact the relative rate
of reproduction of the animal’s ancestors in the
past?
•! Did the behavior have a functional role—a
purpose—in reproduction in the past?
•! Is the behavior an adaptation?
•! Did the behavior evolve by natural selection?
•! zcf
Function
Primate Examples
Grooming langurs
Female gibbon calling
Howler eating young leaves
Summary: Two Categories
•!Proximate Mechanisms (within an
organism’s life)
–!Causation
–!Development (“Ontogeny”)
•!Ultimate (Evolutionary)
Mechanisms (over generations)
–!Phylogeny
–!Function
Levels and NS: Overview
•! Levels of Analysis in
Ethology
–! Proximate
–! Ultimate (Evolutionary)
Tinbergen
•! Natural Selection
–! Darwin
–! Natural Selection
–! Adaptation/Functionality
Darwin
Darwin’s Two Main Contributions
•! Carried out the necessary
research to conclusively
document that evolution has
occurred
•! Discovered the process by
which complex, functional
design originates in living
things: natural selection
Charles Darwin (1809-1882)
Darwin’s Life
•! Family
–! English
–! moderately wealthy (mom was a
Wedgewood)
–! Dad influenced his career options
•! Education
–! Started in medicine at 16
–! Switched to theology at Cambridge
–! Interested in the scientific ideas of
geologist Adam Sedgwick and
naturalist John Henslow
–! At first, didn’t believe evolution
occurred
–! Far more interested in biology than
theology when he graduated
The Beagle
•! Five-year voyage on the
H.M.S. Beagle (1831-1836) at
age 22 with Captain Robert
Fitzroy
•! Galapagos Islands
Darwin’s Influences
Charles Lyell (1797-1875):
geologist who popularized
‘uniformitarianism’
Darwin’s Influences
Thomas Malthus (1766-1834) was an
economist who observed that more
individuals are born than survive to
reproduce; individuals are thus in a ‘struggle
for existence,’ that is, competition
"The elephant is reckoned the slowest breeder of all
known animals, and I have taken some pains to
estimate its probable minimum rate of natural
increase; it will be safest to assume that it begins
breeding when 30 years old and goes on breeding
until 90 years old; if this be so, after a period from
740 to 750 years there would be nearly 19 million
elephants descended from this first pair.” (Darwin)
So, some individuals will reproduce, and others will not. Question:
are “winners” a random selection, or do some individuals have an
advantage over others?
Darwin’s Influences
•! One pair of mice is
capable of producing a
litter of six offspring as
many as six times a
year. Within six weeks,
each offspring can
produce litters of their
own.
Darwin’s Influences
Artificial
Selection
(selective
Breeding
For particular traits)
Darwin’s
Influences
Comparative Anatomy
Vertebrate forelimb
Darwin’s Influences
Fossils
Darwin’s Influences
Geographic distribution of traits: beaks were well-adapted to
local environments on the islands
Adaptive Radiation
Adaptive Radiation in Galapagos Finches
Darwin’s Influences
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Geology (Lyell)
Within-species competition (Malthus)
Artificial selection (breeders)
Comparative anatomy
Paleontology (fossils)
Geographic distribution of traits (finches)
...Natural Selection
Darwin’s Short Definition
“I have called this
principle, by which each
slight variation [in a trait], if
useful, is preserved, by
the term Natural Selection.”
- From The Origin of Species
Natural Selection
•!Natural selection is the process by which favorable
traits that are heritable become more common in
successive generations of a population of
reproducing organisms, and unfavorable traits that
are heritable become less common.
•!Over time, this process can result in adaptations
that specialize organisms for particular ecological
niches and may eventually result in the emergence
of new species.
Natural Selection
Assumption 1: Reproducing entities exist.
Natural Selection
Assumption 2: Variations exist, and they can be
passed on to offspring (heritable variation).
Natural Selection
Assumption 3: Variations have
reproductive consequences.
Natural Selection
Result: over time, the entire population will come to
possess the reproductively superior variation.
Natural Selection
After thousands of generations…adaptations
Adaptation here: camouflage
Natural Selection
•! Assumption 1: Reproducing entities exist.
•! Assumption 2: Variations exist, and they can be
passed on to offspring (heritable variation).
•! Assumption 3: Variations have reproductive
consequences.
•! Result: over time, the entire population will come
to possess the reproductively superior variation—
adaptations.
Darwin’s “Influences”
Why did he wait so long to publish his theory of natural selection?
Alfred Russel Wallace
(1823-1913)
Example: Finches at Daphne Major
Darwin’s Biggest Scientific Problem
•!Darwin realized that
natural selection for
specific traits could lead
to changes in species
through time.
•!However, Darwin lacked
information on how these
traits were passed from
generation to generation.
Genetics
Mendel was the first
to explore the units of
inheritance: genes.
Gregor Mendel (1822-1884)
What do GENES do?
They control the production
specific PROTEINS in living
things…
By stringing up small amino acid
molecules into long protein
strands…
Protein
–! the stuff living things are made of (e.g.,
collagen, enzymes, etc.)
–! Proteins are long molecules that are folded
over upon themselves
–! The components of protein molecules are
smaller molecules called amino acids
(AAs)
Amino Acids
•! There are 20 kinds of AAs that make up all
the proteins that organisms have
–!
alanine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine,
glycine, proline, serine, tyrosine, (essentials:) arginine, histidine,
isoleucine, leucine, lysine, methionine, phenylalanine, threonine,
tryptophan, and valine
•! AAs are made of limited elements: Hydrogen,
Oxygen, Nitrogen, Carbon, and Sulfur (S only
in methionine and cysteine) atoms only
Amino Acids
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AAs are small molecules, but when strung up and folded over on
themselves to form a protein, they can be quite large
AAs are attached by peptide bonds
This protein is 5 AAs long
Amino acid ‘strand’
Each AA is like a bead on a necklace; electrochemical interactions
among neighboring AAs cause the strand to fold over on itself in
specific ways. The folded strand is a protein. Different AA sequences
will make different proteins.
Protein
•! Proteins interact with other substances
(including other proteins) in specific ways that
are determined by their electrochemical
properties.
•! There are only 20AAs out there—a finite
number (though in actuality the story is more
complex than this)
•! Different lengths and permutations of the AAs
that make up AA strands can lead to
countless varieties of proteins
Protein Functions
•! Structural proteins (collagen in skin, keratin in hair
and nails, proteins that make up muscle tissue, etc.)
•! Transport proteins (hemoglobin is a blood cell protein
that transports oxygen to body tissues)
•! Enzymes: proteins that catalyze (speed up) chemical
reactions in the body
•! Immune functions
•! Signaling functions: E.g., neurons in your brain
communicate with each other; these neurons are
proteins (and other substances)
From where do we get amino
acids?
Food!
•! Foods are typically living
(or formerly living)
substances…
•! What substances are in
our food?
Lichtenstein 1962 “Meat”
One organism’s bodies
becomes
Another organism’s body…
Living thing
Organ/Tissue/Cells
Protein
AA to be
restrung up into
some protein
needed by the
eater’s body, as
directed by the
eater’s genes
AA strand
Proteins to AAs
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We eat the tissues of other organisms (plant tissue, meat, etc.)
These tissues are made of proteins
The proteins are cow muscle proteins or plant part proteins (such as
cellulose)
Your body is made of human muscle protein, hair protein, cornea protein,
various neural proteins, etc.
Cow muscle protein is different from human hair protein; how does the
transformation happen?
Answer: your digestive system breaks down the cow muscle protein into its
constituent AAs
Those AA molecules are the raw material that is used to build the proteins
your body needs; they get restrung up into new “YOUR HAIR” proteins
But how do they get restrung up into YOUR HAIR proteins?
Amino Acids to Proteins
…genes
Genes
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Proteins
Genes determine what proteins get built from those raw AA molecules
Genes are protein-coding units of DNA
You eat proteins of other living things, and break the protein into amino
acids; then, genes in your DNA re-string those amino acids into
proteins that YOU need to survive and reproduce
Bodies are made of proteins (fat and carbs and water are essentially
there to service these proteins)
Genes also code for enyzmes, which are proteins that regulate
everything, including development
Other parts of DNA do not code for proteins, and have either no
function (e.g. “hitchhiker DNA), or function for self-regulation, and other
tasks—take advanced biology classes to learn about these very cool
things DNA does
What’s DNA?
DNA
•! Deoxyribonucleic acid
•! A long molecule with a small number of constituent molecules
•! Shape is a “double helix”—think of a ladder that is twisted
DNA
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A sugar-phosphate
“backbone,” (I.e., the “sides”
of the ladder), and “rungs
made up of paired nucleic
acids
There are 4 nucleic acids:
adenine (A), thymine (T),
cytosine (C), and guanine
(G)
Note these are not AAs
A only bonds to T
C only bonds to G
A-T and C-G bonds are weak
Sugar-phosphate bonds are
strong
Lots of “zipping” action
Genes to Proteins
•! Protein synthesis
•! An elegant process that we do not have time to
discuss thoroughly in this class
•! Upshot: the sequence of nucleotides in DNA
determines the sequence of AAs in protein
manufacture (nucleic acid sequence maps to AA
sequence, but not one-to-one, and redundancy is
built into the system)
•! In other words, your DNA determines what proteins
get built out of the AAs that your body extracts from
the foreign proteins you eat
Genes
Proteins
Bodies
+
DNA
molecule
Amino acid
molecules
Cell parts, cells, and tissues
Amino acid strand
Organ
Protein
Body
Natural Selection
•! That was Darwin’s influences,
•! A stripped-down tutorial on NS
•! A brief overview of genes and molecular
genetics
•! Now, common misconceptions
regarding natural selection
Important Point
•! A common misconception when thinking
about natural selection is that there is a
competition or a struggle for existence
among members of different species
•! E.g., thinking about rabbits vs. foxes
•! Or thinking about a species vs. the
many environmental circumstances that
it encounters, including other species
Not just getting food from the
environment...
Getting more food than other
members of your species
Not just avoiding predators…
Avoiding predators better than other
members of your species
Not just avoiding parasites…
Parasitic micro-organisms: roundworm, protozoan, bacterium, fungus, yeast
Avoiding parasites better than
other members of your species do
(mange; a funny website:
http://www.giantmicrobes.com/)
Not just getting good living spaces...
Wedge tail eagle nest
Getting better living spaces than other members of your
species (‘strumming,’ Riechert & Hammerstein)
Funnel spider
Stay Away from Funnel Spiders
Don’t think of it as the environment (which
includes other species) vs. the mouse
Think of it as mouse vs. mouse in an
environment (which includes other species)
Mouse vs. mouse
•! In any population,
not all individuals
survive to reproduce.
Found place to live.
Out-competed other mice for food.
Found a mate.
Successfully avoided predators.
Reproduced successfully.
His kids inherited his genes and the
traits those genes build.
No place to live.
No food.
Couldn’t find a mate.
Predator ate him.
Did not reproduce.
His nonexistent kids did
not inherit his genes and
the traits those genes
build.
Important for mammals, and highlights the
importance of within-species competition to exist
and to reproduce: getting more or better mates
than other same-sexed members of your species
Male red deer
Within-species Competition:
The Bear and the Campers
Still within-species competition, even here, where different
species are still in different niches even though they are all eating
the same fallen gazelle
(1st cheetah, 2nd lions, 3rd hyenas, 4th vultures, next bugs…)
(Back to Tinbergen’s Levels of Analysis)
Trying to understand the Functional Level of Analysis:
Adaptation/Functionality
•! What is an adaptation?
•! Adaptations are functional mechanisms that
have been designed by the process of natural
selection to serve specific problems related to
survival and reproduction.
•! Functional mechanisms have properties and
features that were designed by natural selection.
•! What is a function?
Adaptation/Functionality
Functions are mechanisms that solve specific problems.
Adaptation/Functionality
Functions are specific mechanisms that solve specific problems.
Adaptation/Functionality
Functional mechanisms have specific design features that
solve specific problems.
Most configurations will
not solve the problem.
Adaptation/Functionality
•! Functional mechanisms contain
considerable information about the
problems they were designed to solve.
•! A mechanism’s design features can
often tell us what the function of it is
•! “Reverse engineering”
Reverse Engineering
•! The process of discovering the
technological principles of a
human made device, object or
system through analysis of its
structure, function and
operation. It often involves
taking something (e.g., a
mechanical device, electronic
component, or software
program) apart and analyzing its
workings in detail
Reverse Engineering
Reverse Engineering
Reverse Engineering
(Note: same functions, different design)
Eating leaves
•! Colobines vs. howlers
Adaptation/Functionality
Lungs were designed
by natural selection to
oxygenate blood.
Adaptation/Functionality
How do you identify an adaptation?
(1)! Design Analysis
(2) Comparative method
Analysis of Design
Harvey dissected the heart and
learned that the heart functions
to pump blood by examining
what he saw: chambers, strong
muscles that expand and
contract the chambers, arteries
through which blood leaves a
chamber and gets to other
tissues in the body, valves to
keep it from flowing backwards,
etc.
Analysis of Design
Adaptations show
evidence of:
•! Precision
•! Economy
•! Efficiency
•! Constancy
•! Complexity
•! Reliability
George Williams
Analysis of Design
•! Problems:
–! It is subjective…but let’s be reasonable
–! Adaptations are not always perfectly-designed,
hindering our ability to see, for sure, what their
functions are (human spine)
–! Function of adaptations is not always obvious,
even though we KNOW they are adaptations
(human bipedalism)
The Comparative Method
icthyosaur
Marlin
Dolphin
The Comparative method:
A primate example
•! Testes to body ratio
•! Low in gorillas, where females only
mate with one male while fertile
•! High in chimps, where females mate
with multiple males while fertile
•! Humans: somewhere in the middle
•! What does this tell us about the sexual
behaviors of our human ancestors?
Adaptation/Functionality
What kinds of functions will evolve?
•! Precisely those functions that facilitate, or
enable, reproduction, both directly
(uteruses) and indirectly (hearts).
•! These functions are called adaptations.
•! An organism can be thought of an
integrated set of adaptations.
Functional Level of Analysis in
Ethology (Tinbergen)
•! Did the behavior evolve?
•! Why did the behavior evolve?
•! Does the behavior impact on the animal's
chances of survival and reproduction?
•! Better: how did the trait impact the relative rate
of reproduction of the animal’s ancestors in the
past?
•! Did the behavior have a functional role—a
purpose—in reproduction in the past?
•! Is the behavior an adaptation?
•! Did the behavior evolve by natural selection?
Behaviors as adaptations?
•! The link: neurons
•! Brain cells and their
linkages are made
of protein—proteins
built by genes—and
are thus subject to
the process of
natural selection
•! Brain activity
causes behavior
(recall the
requirements for
being a member of
the animal kingdom;
recall also sea
squirts)
The Modern
Evolutionary Synthesis
•! A union of ideas from different branches in biology that provides a
logical account of the physical process of evolution; links are made
over time with regard to:
–! 1850s-1890s: Darwin’s ideas
–! Early 1900s: Mendel’s work was rediscovered and incorporated
–! Starting in 1920s: work by population geneticists Haldane, Wright,
Morgan, and others
–! Further advances in the understanding of DNA (Watson, Crick, and
Franklin) in mid 1900s
–! Those ideas, combined, comprise the Modern
Synthesis
–! Today, the synthesis is accepted by most working
biologists
•! …In later 1900s: ideas elaborated by Hamilton,
Maynard-Smith, Dawkins, Williams, Trivers, and others
Both
Design Analysis ~AND/OR~ The comparative method
“Survival of the Fittest”
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Some think the phrase explains why gazelles are eaten by cheetahs--cheetahs
are more "fit" so they "survive.”
Problematic terms and meanings:
–! Survival? Nope, it is actually reproduction that is relevant--salmon die to spawn; birth
kills 1/100 women in regions without access to medical care; men risk their lives in
fights over women; male praying mantises are eaten alive by the female during
copulation
–! Fittest? The strongest? The fastest? What about the rodent-like mongrels that
survived the meteor that killed off the dinosaurs 65 million years ago?
–! Fittest? Fittest what? Fittest species? Fittest individual? Fittest genes? Fittest
ecosystem of intracting species?
•!
If you interpret the words to their more specific meanings, and do so accurately,
it ceases to be problematic. Dawkins uses but he is quite explicit about exactly
those terms mean: replication (i.e., reproduction/copying) and thus "survival,"
over generations, of a particular sequence of DNA (such sequences of DNA are
the "replicators"); the DNA molecule itself does not survive, but the ORDER of
it's nucleotide molecules does.
!"#$%$&'
“For the good of the
species”
-Thought experiment: who would reproduce more, an organism that incurred a cost on
its own reproduction to benefit others in its species, or one that hurt others to benefit its
own reproduction? What would the next generation look like?
-Wynne-Edwards vs. Lack’s studies of egg-laying in birds, and interpretations of the data
in Dawkins