Transcript Sexual selection

In This Lesson:
Unit 1
Evolution
Concepts
(Lesson 1 of 3)
Today is Tuesday,
th
September 6 , 2016
Pre-Class:
Who’s your daddy, evolution?
Tell your neighbor something about
him. Also, get a smallish piece of a
paper towel for you/your neighbor.
Turn in:
-Root Words
-Guided Reading (Ch. 22)
http://1.bp.blogspot.com/-onPXq7cad6k/UDBireXSvlI/AAAAAAAAASs/53UrTh8dkH0/s1600/....jpg
Today’s Agenda
• How to make sense of the whole of biology.
• Charles “Chuck D.” Darwin
• Other important figures in evolution.
• Where is this in my book?
– Chapter 22.
By the end of the lesson…
• You should be able to describe the broad view
of evolution.
• You should be able to identify three forms of
selection.
• You should be able to cite evidence supporting
evolution.
• You should know what it means to be
evolutionarily “fit.”
Disclaimer 1: Your Challenge
• This evolution unit is going to be considerably
more rigorous than our last mini-unit.
• You face the following challenges:
– A LOT of vocabulary.
– Being comfortable enough with the material to be
able to link concepts together on a test.
• Good habits:
– “Talking out” the concepts.
– Teaching someone the concepts.
– Meeting with me for extra help.
Disclaimer 2: Belief versus Fact
• I am an evidence-based teacher.
• Evolution has a lot of evidence behind it, to
say the least.
• Therefore I am teaching evolution.
• Period: .
Disclaimer 3: Religion and Evolution
• Just to provide something else to stimulate
your thoughts:
– Pope Francis Praises Evolution and Big Bang
Theory – Snopes
First Up: Challenge Questions
• “Challenge Questions,” for those who have
not been in my biology classes before, are my
way of testing your knowledge of the topics
we are going to cover before we do so.
• This has zero effect on your grades.
• Guessing will likely be necessary.
– Don’t be afraid to do so!
Next Up:
A Compact Evolution Summary (Part 1)
• There are simply not enough resources in the
environment to support every individual organism.
• Specific sets of environmental conditions put oftenintense pressure on organisms to survive:
– Competition with other species/individuals
– Limited resources
– Predation
• Any trait that makes an individual more likely to
survive and reproduce is an enormous advantage.
Next Up:
A Compact Evolution Summary (Part 2)
• How does this advantage arise? Through genetic
mutation.
• If the mutation can be passed down, it’s considered
heritable.
• Because the mutation confers an advantage, it’s known
as an adaptation.
• Heritable adaptations then spread through the
population, increasing in frequency until potentially
giving rise to an entirely new species.
• Thus, the Darwinian line: Descent with modification.
Note
• Please make sure you fully understand that
last slide. You’re gonna need it.
• Questions?
19th Century Perspective
• By the time Darwin started making his
observations, biology had come a long way in
terms of its understanding of how species
change over time.
– Sort of.
• First, the spontaneous generation concept had
been disproven at long last, partially due to
the Redi experiment, which we will now label
just for extra practice.
Labeling the Experiment
• Francisco Redi was one of the first to prove
that maggots don’t come from rotting meat.
• He used three jars: one open, one covered
with netting, and one sealed.
• Into each he placed bits of meat and let it rot.
• His hypothesis was that maggots come from
flies.
– Notice that this is a testable hypothesis.
Labeling the Experiment
•
•
•
•
What’s his control?
What’s his independent variable?
What’s his dependent variable?
What are the constants?
Jar 1:
Flies
Jar 2:
http://faculty.sdmiramar.edu/dtrubovitz/micro/history/Redi.html
No flies
Jar 3:
No flies
Answers
• Control
– Meat in the open jar (Jar 1).
• Independent Variable
– Jar coverings.
• Dependent Variable
– Maggots/flies.
• Constants
– Same jars, same meat, same location.
Da Scientistz
• After Redi, the accepted thinking by most was
that creationism was the answer.
– All species were created by a supreme being
around 3000 years prior to the present.
• So now, the pre-Darwinian evolution-related
scientist-people with-hyphens.
– Note: We’re going to be exploring more evolution
scientists in greater detail. These are perhaps the
most important of the pre-Darwin figures,
however.
Georges Cuvier
• Established paleontology as a field of study.
• Rejected early evolution hypotheses.
• Believing that the biodiversity of fossils is due
to separate creation events.
Thomas Malthus
• An economist by trade,
Malthus identified that
resources are limited.
• There are not enough
resources to support all
individuals, therefore, not
all individuals will survive.
Jean-Baptiste Lamarck
• Characteristics are acquired and then
passed down.
• In other words, a giraffe stretches its
neck out very far, which it then
passes down to offspring.
• Close…
– …but close only counts in horseshoes,
hand grenades, and bad breath.
• In reality, if I were to chop off my
thumbs, my kids would still have
thumbs.
– Acquired traits are not heritable.
The Lamarck Disclaimer
• Most textbooks portray Lamarck as a bit of a…dunce.
– Ha! Acquired traits being heritable. Please.
• Turns out he was actually not really a scientist but more a
philosopher.
– He promoted both the now-called Lamarckian view and the
evolution view.
– Even Darwin was, at one time, a supporter of the acquired traits
deal.
• Most importantly, recent research in epigenetics suggests
that mutations are not entirely random.
– Genes can “jump” (jumping genes) and can activate/deactivate
others in response to environmental stressors.
• Lamarck, even if we label the acquired traits view as his,
was not entirely wrong.
The Big Picture
The Darwinian Revolution
• And then there was Charles Darwin.
• Darwin spent 5 years on the HMS
Beagle as a younger, less bearded
22-year-old, which turned out to be
crucial to his understanding of
descent with modification, aka
evolution.
– All this at a time when Europe
believed in a divine creation event only
a few thousand years before.
• Among other destinations were the
Galapagos Islands, and having small
but isolated populations and
ecosystems to study was essential.
But wait!
• Turns out Darwin wasn’t the
only one onto the whole
evolution thing.
• Alfred Russel Wallace, also
bearded, was working toward
similar conclusions.
• Wallace was working in the
East Indies (think Indonesia),
where he discovered, among
other things, the Wallace
Line.
The Wallace Line
• Wallace noted that on
the west side of the
line, most species were
“Asian-like,” (placental
mammals), whereas
east of the line animals
were “Australian-like”
(marsupials), though
similar.
• The line, therefore, is a
biogeographical
boundary of genetic
isolation.
http://1.bp.blogspot.com/-Qvvxbs1hN1c/UXqP8qTME8I/AAAAAAAABic/I0VIyTgiEl0/s1600/wallace+line.gif
Back to Wallace
• Years after Darwin started formulating his
theory (but never having published it),
Wallace sends Darwin a draft of his findings.
• Darwin realizes he’s going to lose credit.
• Darwin publishes The Origin of Species and
gets credit.
• Ernst Mayr later breaks down Darwin’s ideas
into the following observations and
inferences.
Observations
1. More individuals are born for each species than
survive to reproduce themselves.
2. Populations tend to remain stable except for
seasonal fluctuations.
3. Environmental resources are limited (Malthus,
remember?).
4. No two individuals in a species are exactly alike.
5. The variation among individuals can often be
passed down.
Inferences (therefore…)
1. Individuals in a population must struggle for
existence and not all will survive.
2. Survivors are not “selected” randomly. Those
with traits that make them more “fit” for
their environment (or reproduction) are
more likely to survive.
3. The environment’s favoring of some traits
leads to gradual change in a population
toward the most fit form.
In other words…
Homework: Evolving Views
• To better understand the historical context
behind evolution, you and your lab partner will
do a short research project on a scientist.
– How short? You’re preparing only one PowerPoint
slide (or similar image).
• Your scientist matches the number of your lab
station.
• Next class, you’ll “present” your scientist to other
students.
– Not a formal presentation, FYI.
Fitness
• Included in those inferences was a mention of
the word “fit,” as in, “fitness.”
• Fitness is the measure of an individual’s
adaptation to its environment.
– The best-adapted are the most fit.
• The most fit organisms are those that are
most likely to survive and reproduce
successfully.
IMPORTANT: Fitness Test 
• Who’s most fit?
A. The top predator in a food chain.
B. A mouse that rears 11 total surviving pups and lives 2
years.
C. A 300 year old tortoise with no offspring.
D. The alpha male giraffe in a herd.
• The correct answer is B.
• Key: Fitness only has to do with surviving and
reproducing.
• It has nothing to do with strength, age, et cetera.
Wait…hold on a sec.
• Here we are, halfway through our first
evolution lesson, and I haven’t defined
evolution.
– Though you should have a pretty darn good idea
of it.
• Evolution can best be described as the
development of populations over time in
response to selective/environmental
pressures.
Forms of Selection
• We’re all familiar with natural selection, often called
“survival of the fittest.”
– There’s that “fit” word again.
• The environment exerts certain selective pressures:
– Competition
– Limited Resources
– Predation
• These pressures create enormous advantages for
individuals that are even slightly better-suited for
dealing with them.
– Thus, the environment selects for certain traits and selects
against others.
Forms of Selection
• There’s also artificial selection and sexual
selection, both of which are worth
mentioning.
Artificial Selection
• Canus familiaris is the species
name of all dogs, from
chihuahuas to Great Danes.
• The different “breeds” have
been selected by humans
over time to bring out the
desired traits, like having a
white-tipped tail, or being the
size of a horse.
• Darwin identified this in
pigeon breeds, plants, and
other organisms.
So what is artificial selection?
• Long definition, so I’ll break it into parts. You
write what you need to in order to understand
it:
– Artificial selection, also known as “selective
breeding,” occurs when humans create the
selective pressures…
– …by setting up crosses (mating pairs) that possess
desirable traits…
– …but because humans are doing this, it’s not
natural selection.
Sexual Selection
• The male Indian Peafowl is known for its
dramatic train feathers:
http://upload.wikimedia.org/wikipedia/commons/8/83/Indian_Peafowl.jpg
Sexual Selection
• Here’s the thing: having a big dramatic train doesn’t
help you survive better (it’s actually worse).
– Less aerodynamic.
– Less camouflage.
– Costs resources to produce and maintain.
• However, because having a grand feather display is a
“go big or go home” kind of thing, it is selected for by
peahens, and therefore is an adaptation.
– This same thing explains lots of ornaments in animals and
gives rise to the Sexy Sons Hypothesis, wherein the
flashiest males have flashy male offspring.
So what is sexual selection?
• Sexual selection is a form of natural selection in
which one sex (usually females) apply the selective
pressures.
• Some last comments:
– Females (typically) use ornaments as proxies for genetic
quality.
• “Girl, look at that display. He must have good genes.”
– Ornaments do not have to increase survival to be helpful.
– In some cases, females may adjust their own investment in
their young according to the differential allocation
hypothesis.
• In birds, females may lay different numbers of eggs, lay eggs with
more favorable nutrient balances, or care for the young
differently based on the genetic quality of the male.
Proof of Proxy
• Biologists have noticed proof that the whole
“females use flashy behaviors or displays as
evidence of genetic quality” thing exists.
– How?
• Take the peafowl again.
• Turns out, there’s a very strong correlation
between fanciest display and strongest immune
system.
– Pretty cool.
One last sexual selection example…
• Zebra Finches:
• Males allocate
carotenoid pigment to
their beaks, legs, and
cheek patches to
make them bright red.
– Females love it.
• Give males green leg
bands and suddenly
they’re not so
attractive.
http://www.rbgsyd.nsw.gov.au/__data/assets/image/0011/88535/Taeniopygia_guttata_Zebra_Finch_620.JPG
I know you
think my
beak is
attractive.
What drives selection?
• Okay, great, some traits are desirable (adaptations)
and others aren’t.
– This still doesn’t explain change.
• These changes are brought about by random
changes in DNA – mutations.
– “Random” is the keyword here.
– Would I get a lot of women if I could fly? Probably.
– But, that trait needs to arise by mutation, and it needs to
be heritable – I need to be able to pass it on.
• As you can imagine, the work of Darwin and Mendel
combined make all of biology make sense.
Mutation and Selection in Action
• Peppered moths exist in one of two color
morphs – light or dark.
• Generally, light colored moths blend in with
their environment much more effectively.
– At any given time, there are more light colored
moths around because the dark ones get
eaten.
– The environment selects for light colored
moths and against dark colored moths.
• However, increased air pollution in the
Industrial Revolution temporarily darkened
the bark of trees throughout Great Britain.
– Suddenly, the favorable trait was to be dark
colored.
Peppered Moths
• Population numbers shifted dramatically as a
result of the change in the environment, only to
change again (back to favoring light colored
individuals) when pollution cleared up years later.
• Importantly, no individual moth ever changed
color.
– Instead, evolution occurred between generations –
light colored moths briefly began to be eaten more
often prior to reproduction, meaning the gene(s) for
being light colored were less abundant in the
population than those for being dark colored.
Other Examples
• Antibiotic and insecticide
resistance are becoming
major issues today.
• Not all individuals are killed,
allowing those that are
resistant to pass on their
genes and give rise to an
entire resistant population.
• Think MRSA:
– Methicillin-resistant
staphylococcus aureus.
Antibiotics and Selective Pressure
• Using (and misusing) antibiotics (or even Purell) is
a cause for developing resistance.
– The antibiotics create INTENSE selective pressure on
bacteria, which have a relatively high mutation rate.
– Any mutation on the part of the bacteria that allows
for drug resistance will lead to rapid growth of drugresistant bacteria.
• The solution?
– Use a wide array of treatments and don’t apply such
intense pressure. Use antibiotics (et cetera) as
minimally as possible.
Uh…excuse me…
• You know how many diseases are hereditary?
– Like, Type I Diabetes, for example?
• Exactly how might these disease-causing alleles
still be in the gene pool?
– Natural selection would predict that these individuals
should be at a disadvantage and the alleles slowly be
“shuffled out.”
• Two possibilities for why they’re here:
– Modern medicine is preventing their removal
(unlikely).
– They’re vestigial alleles. As in, they serve(d) a
different purpose.
• Survival of the Sickest excerpts.
Evidence for Evolution
• Fossils
– Unlike Cuvier’s thoughts, the fossil record (in rare areas of relative
completion) shows gradual changes through time.
• Geographic Distribution
– Fossils are distributed only in areas where related species could have
lived.
• Homologous Structures*
– Similar anatomical traits exist between closely-related species.
• Vestigial Structures
– Structures that carry no apparent present function are maintained by
current populations – they must have served a purpose in the past.
• Embryology
– Early developmental stages look very similar in closely-related species.
• DNA
– The big one – DNA is strikingly similar between closely-related species
(99% similar DNA between humans and chimpanzees & bonobos).
More About Vestigial Structures
• Vox – Evidence of Evolution That You Can Find
On Your Body
• Note: At the time I am writing this slide, here’s
the top comment from YouTube:
Homologous Structures
• Simply put, these come up all the time in bio tests.
• Homologous structures are features of organisms’
phenotypes that look similar because they come from
a common ancestor.
– Example: A horse’s hoof and a dog’s foot have similar bones
because they share a common ancestor.
• Analogous structures are features of organisms’
phenotypes that look similar but the similarity is a
coincidence because they evolved separately.
– Example: A bird’s wing and a bat’s wing look somewhat
similar, but each evolved independently.
Closure
• TED: Paul Andersen – The Five Fingers of
Evolution
• TED: Alex Gendler – Myths and
Misconceptions About Evolution
Closure: Chicken or Egg?
• So, which came first, the chicken or the egg?
– You should be able to answer this now, in one of two ways.
1. Reptiles evolved before birds, and therefore were
laying eggs before birds.
– Since proto-reptiles are also thought to have given rise to
birds, it makes sense that birds also lay eggs.
2. Given that evolution occurs between generations,
the parent of the first chicken was not a chicken.
– Therefore, the egg came first.