Download Evolution and Diversity

Observing Variation in Traits
• Copy the following chart into your notes:
Animal
Bird
Fish
Dog
Snake
Rabbit
Means of locomotion
Trait used for
locomotion
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Look at each picture and determine the means of locomotion for each animal and
write it in the chart. (How do they get around?)
Then determine what trait is used for their specific type of locomotion and write
it in the chart.
Charles Darwin
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From England
A naturalist (studied natural history)
Sailed all over the world on the H.M.S. Beagle
Made numerous observations & collected
evidence that led him to propose the Theory
of Evolution
Darwin’s Curiosity
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He found it interesting that many so plants and animals are remarkably
well suited to their environment
He was impressed by the many different ways organisms survived and
how they produced offspring
He was puzzled by where different species lived and did not live, even
though environments are similar. (for example, why were there no
rabbits in Australia, even though there were plenty of suitable
environments for rabbits?)
He collected fossils and eventually realized that some fossils belonged to
species that had disappeared, and he wanted to know why and how they
might be related to living species.
To find the answers to these questions and so many
more, Darwin made many, many OBSERVATIONS. . .
The Galapagos Islands
• Influenced Darwin the most
• Islands were close together but had
very different climates
• Fascinated by the land tortoises and
the various different, yet similar birds
• He noticed that the characteristics of
many plants & animals varied
noticeably among the different islands
of the Galapagos
On the Origin of Species
• Darwin used his observations in combination with other
scientific developments of his time to develop ideas and
theories about why species were so diverse
• Eventually, he published his work in a book called On the
Origin of Species.
• In this book, he introduced the concepts of natural selection
and evolution
Inherited Variation &
Artificial Selection
• Variation – how things are different from each other; not just in looks, but
also in structure and behavior
• Darwin observed that individuals within a species are different. For
example, human beings are members of the same species, but we are all
different. Some plants of the same species produce larger fruit than
others, and some cows produce more milk than others.
• Darwin also learned that these differences can be passed down from
parents to offspring – this is called inherited variation
• Darwin noted that plant and animal breeders would only breed the
individuals with the most beneficial traits, so that they could produce new
individuals with those same beneficial traits
• This is called artificial selection – In artificial selection, nature provides the
variation, and humans select those variations that they find useful
Artificial Selection Exercise
• http://wps.prenhall.com/wps/media/objects/
486/498193/CDA1_1/CDA1_1a/CDA1_1a.htm
• http://wps.prenhall.com/wps/media/objects/
486/498193/CDA1_1/CDA1_1b/CDA1_1b.htm
Evolution by Natural Selection
• Darwin saw that people could force evolution, but wanted to see if it
occurred naturally (in nature, without humans interfering)
• He soon learned that nature also has a form of selection, or a way of
selecting which traits are passed down and which ones are not
• He identified 3 main processes that worked in nature to select specific
traits to be passed down:
1. The struggle for existence
2. The survival of the fittest
3. Descent with modification
• Defined – members of each species compete regularly to
obtain food, living space, and other things necessary for life.
• Causes of this struggle:
– High birth rates lead to over population
– Shortage of life’s basic needs or resources
• Examples:
– Predators that are faster catch more prey than the slower
– Prey that are faster or better camouflaged can better
avoid being caught
Survival of The Fittest
• Fitness – the ability of an organism to survive & reproduce in a specific
environment
• Fitness is a result of adaptations
• Adaptation – any inherited characteristic that increases the organism’s
chance for survival
• Successful adaptations make the organism better suited for their
environment and therefore increase the organism’s chances of survival
and reproduction
• Since fitness is a result of adaptations, the better the adaptation, the
higher the fitness
Survival of The Fittest
• Those with higher fitness levels are more likely to survive and
reproduce, and their traits will be passed on
• Those with lower fitness will die and leave few, if any, offspring and
their traits will not be as likely to be passed on
• Darwin called this Natural Selection because the traits that get
passed down are, in a way, selected by nature, or they are selected
in a natural way.
• Natural Selection takes place without human control or direction
• Over time, natural selection results in more favorable traits being
passed down and this increases the fitness of the whole population
and species.
• Natural Selection cannot be seen directly. It is seen by the changes
in populations over many generations
Examples of Natural Selection
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Peppered Moth - Many times a species is forced to make changes as a direct result
of human progress. Such is the case with the peppered moth (Biston betularia). Up
until the Industrial Revolution, these moths were typically whitish in color with
black spots, although they were found in a variety of shades. As the Industrial
Revolution reached its peak, the air in London became full of soot, and the oncewhite trees and buildings that moths used for camouflage became stained black.
The birds began to eat more of the lighter-colored moths because they were more
easily spotted than the darker ones. Over the course of a few months, dark moths
started appearing in the area and lighter moths became scarce. Once the Industrial
Revolution peak passed, lighter moths made a comeback.
Examples of Natural Selection
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Pesticide-Resistant Insects - The more a pesticide is used, the greater the chance
that the insects targeted will develop immunity to the chemical. Pesticide
resistance is not only very common, but it also usually happens rather quickly.
Sometimes all it takes is a single generation. Imagine that a group of insects
survives the pesticide and is able to reproduce. More likely than not, the offspring
will be resistant to the pesticide from birth. Those that are not immune will die,
while the strongest will survive. Since many insects reproduce quickly, several
generations can be born within months or even weeks. By the time a few
generations have passed, all insects are likely to be resistant to the pesticide.
Survival of the Fittest
• http://www.gamvak.com/Kids_Games/Survival-Of-The-Fittest
• Conduct the following activities to see who “wins”
1. Play Simon Says – demonstrate ability to follow directions.
2. Musical Chairs – demonstrate reaction time
3. Sprints – demonstrate speed
4. 3 legged race – demonstrates teamwork
Add up points. The students with the higher numbers have higher fitness and
are therefore more likely to survive and reproduce.
Descent with Modification
• Darwin realized that since adaptations were
passed down, there was reason to believe
that species today might look different than
their ancestors
• Descent with Modification –
– every living species has descended , with some
changes, from other species over time
– All living things are related to each other
– Common descent – all species, living and extinct,
came from common ancestors
Evidence of Evolution
• Fossil Record: the remains of ancient life
that are found in rock layers and give us a
history of life on Earth
• Geographic Distribution of Living Species:
Darwin realized that there were species
that were similar, yet different. He
realized that similar animals in different
locations were the product of different
lines of evolutionary descent.
• Homologous Body Structure: Homologous
structures may not necessarily perform
the same function but they share a
common ancestral origin.
• Similarities in Embryology – embryos or
early stages of many animals are very
similar; cells develop in the same order
even though they end up being very
different
Summary of Darwin’s Theory
• Darwin’s Theory of Evolution is summarized as follows:
– Individual organisms differ and some of these differences
(variation) is heritable
– Organisms produce more offspring than can survive, and many
do not survive to reproduce
– Because more organisms are produced than can survive, they
compete for limited resources
– Individuals best suited for their environment survive and
reproduce more successfully, and they pass their traits to their
offspring, causing species to change over time.
– Species that are living today are descended with modification
from a common ancestral species that lived in the distant past.