natural selection - flipped out science with mrs. thomas! identify some changes in traits that have...
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7 . 1 1 C I D E N T I F Y S O M E C H A N G E S I N T R A I T S T H A T H A V E
O C C U R R E D O V E R S E V E R A L G E N E R A T I O N S T H R O U G H
N A T U R A L S E L E C T I O N A N D S E L E C T I V E B R E E D I N G
NATURAL SELECTION
COULD YOU HAVE RIDDEN A HORSE MILLIONS OF YEARS AGO?
• Horse evolution goes back more than
55 million years
EVOLUTION OF THE HORSE THE ECOLOGICAL PRESSURES FACING THE SPECIES DETERMINED THE TYPE OF DIFFERENCES, OR VARIATION
The development of larger limbs
and hooves allowed horses to
spread out and become more
successful in grassland habitats
as they developed.
WHY CAN YOU RIDE ONE NOW?
• Natural selection caused some changes in
horses, and humans participated in selective
breeding which both domesticated the horse
and made specialized organisms.
NATURAL SELECTION – VISTA!
• Natural selection causes populations of
living things to change over time.
• In fact, it can be broken down into five
basic steps, abbreviated here as V.I.S.T.A.
• V - Variation
• I - Inheritance
• S - Selection
• T - Time
• A - Adaptation
WHAT EXACTLY IS NATURAL SELECTION?
• The process by which individuals that are
better adapted to the environment survive
and reproduce more successfully than other
members of their species
• These are changes in genetics traits over
many generations
HOW DO GENETICS CHANGE OVER SEVERAL GENERATIONS?
• Changes occur over time from either natural
selection or selective breeding
• You now know that when DNA is copied,
mutations (mistakes) can occur
• Sometimes those mistakes are fatal, some
times they make no difference in survival,
and sometimes, every once in a great while,
that mutation becomes critical to survival
VARIANCE OR VARIATION:
• Members of any given species are seldom
exactly the same, either inside or outside.
• Organisms can vary in size, coloration, ability
to fight off diseases, and countless other
traits.
• Such variation is often the result of random
mutations, or "copying errors," that arise
when cells divide as new organisms
develop.
VARIANCE OR VARIATION:
• If the organism survives and reproduces, their
genes get passed on
• If the gene is either neutral or positive, it is more
likely that the mutation will be passed on to the
next generation
• Differences in color, for instance, aid some
individuals in camouflaging themselves from
predators. Sharper eyes and claws help an eagle
catch its dinner. And brighter coloration improves
a male peacock's chances of attracting a mate.
• Next, let’s look at a few examples of variations
EXAMPLE 2 OF VARIETY OF TRAITS: COUNTER-SHADING IN MARINE LIFE
• Upper side of the animal is darker than the lower
side, blends in with sea floor
• Lower side of organism is lighter, organism blends in
with its surroundings – in this case the sky
Which do you think is better for the survival for each of
these species?
EXAMPLE 4 OF VARIETY OF TRAITS:CLAWS IN BIRDS
Variation in talon size and shape due to hunting technique.
INHERITANCE:
• When organisms reproduce, they pass on their
DNA--the set of instructions encoded in living
cells for building bodies--to their offspring.
• And since many traits are encoded in DNA,
offspring often inherit the variations of their
parents.
• Tall people, for example, tend to have tall
children.
SELECTION: SURVIVAL AND REPRODUCTION
• Environments cannot support unlimited
populations.
• Resources are limited, more organisms are born
than can survive: some individuals will be more
successful at finding food, mating or avoiding
predators and will have a better chance to
thrive, reproduce, and pass on, their DNA.
• Small variations can influence whether or not
an individual lives and reproduces.
TIME:
• In generation after generation, advantageous
traits help some individuals survive and
reproduce.
• And these traits are passed on to greater and
greater numbers of offspring.
• After just a few generations or after thousands,
depending on the circumstances, such traits
become common in the population.
ADAPTATION:
• The result is a population that is better suited--better
adapted--to some aspect of the environment than
it was before. Legs once used for walking are
modified for use as wings or flippers. Scales used for
protection change colors to serve as camouflage.
WHO FIGURED THIS OUT?
• CHARLES DARWIN – 1809-1882
• Most people in the world did not
become aware of the theory of
evolution until 1859, when Charles
Darwin published his book On the
Origin of Species by Means of
Natural Selection.
DARWIN’S OBSERVATIONS
• This book described the observations and evidence
that he collected over 20 years of intensive
research, beginning with a five-year voyage around
the world on a British research ship, the HMS Beagle.
• During this five-year voyage, Darwin was able to
make observations about plants and animals
spread around the world, and to collect specimens
to study when he returned to England.
THE GALAPAGOS ISLANDSDarwin’s best known
discoveries were made on
the Galápagos Islands, a
group of 16 volcanic islands
near the equator about 600
miles from the west coast of
South America.
This isolation of the islands
allowed geographical
isolation to take place
GEOGRAPHIC ISOLATION
• Species evolved differently on the islands than on
the “mainland”
• Darwin was amazed by the array of life he saw on
the Galápagos Islands. He saw animals unlike
anything he had ever seen before.
• For example, the iguanas (large lizards) differed
between islands. The members of one iguana
species spent much of their time swimming and
diving underwater for seaweed, while those of
another iguana species lived on land and ate
plants.
SIMILARITIES AND DIFFERENCES
Marine Iguanas of the Galapagos
Large claws for gripping slippery rocks, eat seaweeds
Green iguanas in South America
Smaller claws for climbing trees, eat leaves
Marine Iguanas
WHAT DOES THIS MEAN?
Key understanding: mainland species were still related to the island species -
Curiously, they looked different, ate different foods, and behaved differently, but still had some similarities
So how did this happen?
Answer: gradual changes over many generations
Darwin’s observations
• Of particular interest were the finches on these islands
• They had varied sizes and shapes of the beaks. This observation made him wonder….
WHY?
FROM ONE FINCH…
• There are now at least 13 species of finches on
the Galapagos Islands, each filling a different
niche on different islands. All of them evolved
from one ancestral species, which colonized
the islands only a few million years ago.
WHAT DARWIN LEARNED FROM THESE FINCHES
• The one species of finch gradually evolved into separate species because of food sources and other environmental factors such as amount of water available
For example:• Beaks highly adapted to food source
• Large beaks - meant there was little rainfall because the seeds were large & tough
• Small beaks - Heavy rainfall – seeds – small & soft
• Other adaptations were sharp beaks for finding and eating insects, wide beaks for cracking seeds
MORE ADAPTATIONS
• Darwin studied hundreds more animal
and plant species. After nearly 20
years of research, he proposed
his theory of evolution by natural
selection.
Darwin’s Conclusions – based on his research:
• Species have changed over generations through adaptations• The changes allow them to survive and reproduce in a new environment. • Darwin proposed that evolution occurs by means of natural selection• New species may form when a group of individuals is isolated from the rest of the population
Darwin’s 5 key points in theTheory of Natural Selection:
1. Populations have (genetic) variations.
2. Some variations are favorable.
3. More offspring are produced than
survive
4. Those offspring that survive have
favorable traits. 5. A population will change over time.
DARWIN’S CONTEMPORARIES
• Lamarck and Wallace had similar findings as Darwin• Wallace called the changes in species over time “evolution”.
Jean-Baptiste Lamarck, 1744-1829
Alfred Russell Wallace, 1823-1913 (with Darwin)
YOU MAY HAVE HEARD OF…
• Lamarckism (or Lamarckian inheritance) is
the idea that an organism can pass on
characteristics that it acquired during its
lifetime to its offspring.
OVERPRODUCTION
• What’s the point of so many offspring?
• Only the “fittest” survive, not all of your
offspring will survive long enough to
reproduce and pass on genetic heredity–
but some will!
COMPETITION
• Resources are limited! There is only so much
food, space, water and shelter
Members of the same species must compete
with each other, only the fittest survive
AND VARIATION ….
Any genetic difference between individuals of the same species
• very important in natural selection
• the stronger individuals survive and reproduce
• offspring with helpful traits will survive and then pass along those traits to their offspring
What might those
traits be?
TO SUM IT UP…
• Watch this: Natural Selection
video