Transcript Document

EVOLUTION
Agenda
• “E” experiment
• “U” experiment
• Squirrels
-Food web
-Natural selection
• Weekly reminders
• Q&A
“E” Experiment
For this seminar, you will simulate an example of natural
selection with the words you use. When your instructor
announces "START," you should have a chat about the
weather in your area. The only hitch is that you may not
use the letter 'e' in anything that you type. Any words that
contain the letter 'e' will be ignored. You and your
classmates will talk about the weather in your area for
five minutes total, after which your instructor will
announce "STOP," and you will be allowed to use the
letter 'e' again.
How is th_ w_ath_r?
Image credits: Microsoft Clip Art
Reflect on your conversation and discuss the following
topics with your classmates:
1) In your new, 'e'-free environment, what
adaptations to language did you and your
classmates make?
2) What things were more difficult to talk about,
and why?
A “u” free environment
Image credits Microsoft Clip Art
A “u” free environment
3) If you were to live in a 'u'-free environment, what
other letters might struggle and die out?
Possible endangered “u” things…
U-turn, Ugly duckling, Ulna and ulcerative colitis,
underwear, unemployed, unhappy, uncles, or under
water, undertow, understory, upstairs, upright, upside
down cake, or upset, Utah, USA, and Uranus, uranium,
Universe, unicorn, uniform, unicycle, unzip Umbrellas
and umpires Utensils and utopia, Urgent and urchin,
Ukuleles, Use us, Union, united, utility, unit, udder, ultra,
unable, ultimate…
Muted, bugle, bug, dug, jug, mug, pug, rug, you, menu,
thou, ecru, thru or through, bandeau, beau, caribou,
fondue, Haiku tableau, snafu, tiramisu, tofu, trousseau,
tutu, bureau, plateau, bayou, luminosity.
Squirrels and the food web
Image credit: Microsoft Clip Art
Squirrels and natural selection
4) Think about this experiment as a way to show how changes in
environment force creatures (like you) to adapt and change. Now,
think about squirrels. What might happen to them if all the oak trees
(and therefore acorns) died out?
What adaptations might they have to make to adjust to the acornfree world?
How might these changes affect their body structures?
After 50,000 years of living in an acorn- free world, how might
squirrels look?
Why does this kind of evolutionary change take so long?
Mutations and natural selection
Science explains that all living things share common ancestors,
and over time, natural selection gives rise to variations and
changes. A human example of natural selection is the ability to
digest lactose. Lactose is the main sugar in milk composed of a
glucose molecule linked to a galactose molecule. The human
digestive system has not always been able to digest lactose. It took
a genetic mutation (natural selection) to enable humans to digest
lactose.
Not everyone has this mutation. Most northern Europeans,
whose ancestors domesticated cattle, have the mutation and can
digest lactose. Descendants of cultures who did not raise cattle for
milk (most Asians and many Africans) do not have the mutation and
cannot digest lactose. In the U.S. up to 15% of European
descendants, 75-80% of Africans and Latinos, 75-100% of
American Indians and Asians are lactose intolerant.
Another example…
Anyone whose family has been touched by hereditary disease has
probably asked: If natural selection is supposed to get rid of harmful
genetic traits, why are there so many hereditary diseases in the first place?
Scientists have long known that sickle cell anemia, which causes blood
cells to deform, protects against malaria (a fatal parasite that eats
hemoglobin). There is a high frequency of the sickle cell genes in malaria
endemic regions. Scientists believe this to be due to the advantage against
fatal malaria.
The sickle cell gene is found widely throughout Africa and in countries
with African immigrant populations (e.g., the Caribbean, UK, and US), in
some Mediterranean countries (e.g., Greece), the Middle East, and parts
of India. In my opinion, sickle-cell anemia is an unfortunate by-product of
evolutionary adaptation. When people inherit one copy of the sickle-cell
gene, they acquire a beneficial resistance to malaria that has ensured the
gene's survival. When people inherit two copies of the sickle-cell gene, the
result is a deadly disease.
Geographic Isolation
In response to a predator, the tiny brown anolis lizards on several
Caribbean and Bahamian islands underwent natural selection
twice: first for long legs, then for short legs.
A hurricane flooded the islands and swept away the brown
anolis lizard’s natural predator, the larger, ground-dwelling curlytailed lizard (Leiocephalus carinatus). Researchers then
reintroduced the curly-tailed lizard. After six months, researchers
observed that the surviving brown anolis lizards had longer legs
than those on islands without curly-tailed lizards.
After a year, the researchers observed that the process of
natural selection had reversed. The surviving brown anolis lizards
now had shorter legs than those on islands without curly-tailed
lizards. So, what happened?
Further Explanation
When the brown anolis lizard lives without predators, it stays mostly
on the ground, where long legs make for fast moves. In the first six
months, the brown anolis lizard stayed on the ground, dodging the
curly-tailed lizards.
However, after a year of running from the curly-tailed lizards, the
brown anolis lizards learned to climb up into trees and bushes,
where shorter legs make for better agility.
So, do you think natural selection is a long-term process, a shortterm process, both, or neither? Why?
Fish
The Antarctic ice fish species of today has no red blood cells
(hemoglobin). Red blood cells thicken blood, making it difficult to
pump in extreme cold. The Antarctic ice fish species has developed
other circulatory features (think fish antifreeze) instead. This fish’s
blood, rather than being red, is colorless and nearly transparent.
Scientists, however, discovered that the gene for hemoglobin
remains in the fish’s DNA.
Natural selection leaves its signature in DNA. This tells us the
Antarctic ice fish evolved from red-blooded ancestors in warmer
waters.
Class, what do you think will happen to this fish species if the water
temperature rises in the Antarctic?
Questions?
Image credit: Microsoft Clip Art