The idea that life evolves was first Proposed by Lucretius 1900
years ago!
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His idea was not fully considered until The middle of the
1800s. In 1859, the English naturalist Charles Darwin published
convincing Evidence that species evolve, and He proposed a
reasonable mechanism Explaining how evolution occurs.
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Like all scientific theories, the theory Of evolution has
developed over Decades of experimental data. Today almost all
scientists accept That evolution is the basis for the Diversity of
life on Earth.
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The theory of evolution has 4 parts: 1) Variation exists with
the genes of Every population of species (the results of mutation)
2) In a particular environment, some Individuals of a population or
species Are better suited to survive and Have more offspring than
others.
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3) Over time, the traits that make Certain individuals of a
population Able to survive and reproduce Tend to spread in that
population. 4) There is clear proof from fossils And many other
sources that living Species evolved from organisms That are
extinct.
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In 1831, Darwin became the Naturalist for the naval voyage of
The HMS Beagle. The purpose of the voyage was to Survey the coast
of South America.
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During his voyage on the Beagle, Darwin found evidence that
challenged The traditional belief that species Are unchanging. As
Darwin visited the many places On his voyage, he saw things that
Seemed as if they could only be Explained by a process of gradual
change.
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On the Galapagos Islands, Darwin Discovered different varieties
of Finches that had different beaks. The birds looked similar, but
had Evolved beaks that suited the Environment where they ate.
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When Darwin returned from his Voyage, he continued his lifelong
Study of plants, animals, and geology. He didnt report his findings
called evolution until much later.
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After reading an essay by Thomas Malthus, Darwin made a key
association, Individuals that have physical or Behavioral traits
that better suit Their environmental are more likely To survive and
reproduce than those That do not have such traits.
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Darwin called this process by which Populations change in
response To their environment, natural selection. The changing of a
species that results In its being better suited to its Environment
is called adaptation.
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In 1859, Darwin finally wrote down His ideas of evolution and
natural Selection in a book called On the Origin of Species by
Means of Natural Selection Many people were deeply disturbed by It,
including the church because it Hints that humans may have evolved
from apes.
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Darwins ideas have been updated Natural selection causes change
Within population. Such as, broccoli, cauliflower, Brussels
sprouts, and cabbage all Come from the same plant!
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In other words, natural selection Causes the frequency of
certain Alleles in a population to increase Or decrease over time.
Isolation leads to species formation.
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Isolation is the condition in which 2 populations of the same
species Cannon breed with one another. This happens all the time,
and is why There are many different types of Squirrels, and is the
reason that Darwin saw different types of The same bird!
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Extinction leads to species replacement. Over long periods of
time, events such As climate changes and natural Disasters result
in some species Becoming extinct, which means That they disappear
permanently.
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Fossils provide an objective record Of evolution. A fossil is
the preserved or Mineralized remains or imprint Of an organism that
lived long ago.
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Today Darwins theory is almost Universally accepted, based on a
Large body of supporting evidence, Most scientists agree on the
Following 3 points 1) Earth is about 4.5 billion years old. 2)
Organisms have inhabited Earth for Most of its history. 3) All
organisms living today evolved From earlier, simpler
life-forms.
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Although the fossil record will never Be complete, it presents
strong Evidence that evolution has Taken place. Paleontologists,
scientists that study Fossils, can determine that age of Fossils
fairly accurately by using Radiometric dating.
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A common ancestor is a species From which 2 or more species
Have diverged. A phylogenetic tree shows how organisms are related
through evolution. Biological molecules contain a record Of
evolution.
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Anatomy and development Suggest common ancestry. Comparisons of
the anatomy of Different types of organisms often Reveal basic
similarities in Body structures.
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For example, sometimes bones (or other structures) are present
In an organism but are reduced in Size and either have no use or
Have a less important function. Such structures are considered to
be Evidence of an organisms Evolutionary past.
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These structures are called Vestigial structures.
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Does evolution occur in spurts? The model of evolution in which
Gradual change over a long period of Time leads to species
formation Is called gradualism. The model of evolution in which
periods Of rapid change in species is separated By periods of no
change is called Punctuated equilibrium.
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Darwin wrote: Can we doubt that Individuals having any
advantage, However slight, over others, would Have the best chance
of surviving And of procreating their kind?
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There are 5 main elements to Natural Selection 1) All species
have genetic variation. 2) The environment presents many Different
challenges to an individuals Ability to reproduce.
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3) Organisms tend to produce more Offspring than their
environment Can support; thus, individuals of a Species often
compete with One another to survive. 4) Individuals within a
population that Are better able to cope with the Challenges of
their environment tend To leave more offspring than those Less
suited to the environment.
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5) The traits of the individuals Best suited to a particular
Environment tend to increase In a population over time.
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The key lesson scientists have learned About evolution is that
the Environment dictates the direction And amount of change. A well
studied example of natural Selection in action is Industrial
melanism.
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Industrial melanism is the darkening Of populations of
organisms over Time in response to industrial pollution. The best
known case is the European Peppered Moth.
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The formation of new species Begins with small changes. The
accumulation of differences Between groups is called divergence.
Biologists call the process by which New species form
speciation.
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Overtime, populations of the same Species that differ
genetically Because of adaptations to different Living conditions
become what Biologists call ecological races. Eventually races may
become so Different that they can no longer Interbreed
successfully, biologists Then consider them a new species.
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What keeps a new species separate? Reproductive isolation is
the inability Of formerly interbreeding groups To mate or produce
fertile offspring. This may happen due to geographical Reasons, or
environmental reasons.