Download Evolution - cccoe.net

EVOLUTION AND NATURAL SELECTION
Evolution is defined as the change in species over
time. Darwin theorized that evolution occurs
through a process known as natural selection. This
process is broken down into four parts:
•
•
•
•
Overproduction
Genetic Variation
Struggle to Survive
Successful Reproduction
OVERPRODUCTION
Overproduction is a process in which each species
produces more offspring than will survive to
maturity.
GENETIC VARIATION
The individuals in a population are slightly
different from each other. Each individual has a
unique combination of traits, such as color, size,
speed, and the ability to find food. Some traits
increase the chances
of survival and
reproduction.
These beneficial traits
are called adaptations.
Variations are
genetic and can be
inherited.
STRUGGLE TO SURVIVE
Because there is only so much food, water, space,
and other resources available in the environment,
not all individuals will
live to adulthood.
Those best adapted will
have a better chance
of survival. Nature, or
the environment selects
which organisms live
and which die. This
struggle is often referred
to as “Survival of the Fittest”.
SUCCESSFUL REPRODUCTION
The individuals that are well adapted to their
environment, that is, those that have better traits
for living in their environment,
are more likely to survive
and reproduce. Their
traits are thereby passed
on to their offspring. The
individuals that are not
well adapted to their
environment are more
likely to die early or
produce few offspring.
NATURAL SELECTION IN ACTION
When an effective insecticide is used on a
population of insects, most insects are killed, but
few may survive. These survivors have genes
that make them resistant to the
insecticide.
NATURAL SELECTION IN ACTION
The survivors then reproduce, passing the
insecticide-resistant genes to their offspring.
NATURAL SELECTION IN ACTION
In time, the replacement population of insects is
made mostly of individuals that have the
insecticide-resistant genes.
NATURAL SELECTION IN ACTION
Ultimately, when the same kind of insecticide is
used on the insects, only a few are killed because
the overall population has
become resistant to that
insecticide.
EVIDENCE OF EVOLUTION
There are five pieces of evidence scientist use
to support the theory of evolution. They are:
•
•
•
•
•
The Fossil Record
Homologous Structures
Vestigial Structures
Embryonic Structures
DNA Evidence
THE FOSSIL RECORD
• Fossils are the preserved
remains or traces of an
organism that lived in the past.
The millions of fossils that
scientists have collected, is
called the fossil record.
THE FOSSIL RECORD
• According to the fossil record, over 90% of the
organisms that once lived on the Earth are now
extinct. In addition, there is no fossil evidence that
organisms alive today were here long ago. However,
the organisms alive today have features that
resemble life of the past. What happened to the
species that lived long
ago, and where did the life
of today come from? The
evolutionist explanation
is that species from long
ago have changed into
the species alive today.
HOMOLOGOUS STRUCTURES
Scientists have observed that
many different organisms have
structures that are quite similar.
For instance, when comparing a
human hand, cat leg, dolphin
flipper, and a bat wing, we find
nearly identical bone patterns.
Why would structures specialized for such different
functions such as grasping, walking, swimming and
flying be so similar? The evolutionist conclusion is
that these different animals must have evolved from
a common ancestor.
VESTIGIAL STRUCTURES
Vestigial structures are structures that no longer serve a
function in the living organism. For instance, humans
have a tail bone that serves no apparent function. In
addition, the modern whale has a series of bones near
the base of the skeleton that resemble hip bones. Hip
bones serve the function of allowing land animals to
walk. Why would a
whale have hip bones?
The evolutionist
conclusion is that the
whale must have
evolved from a land
walking creature.
VESTIGIAL STRUCTURES
Fossil evidence also supports the theory that the
modern day whale evolved from a land walking
animal.
55 Million Years Ago
40 Million Years Ago
50 Million Years Ago
46 Million Years Ago
EMBRYONIC STUCTURES
A developing baby is called an
embryo. Embryos of very
different organisms such as a
chicken, rabbit, and human have
embryos that look nearly
identical. During the early stages
of development, all have a tiny
tail and gill slits in their throats.
The conclusion is that all of these
organisms have a common
ancestor. It is thought that the embryo is like a
window through evolutionary time. The ancestors
of these species once had tails and gills.
DNA EVIDENCE
The DNA that codes for all life
on this planet is composed of the
same four nitrogen bases,
adenine, guanine, cytosine, and
thymine. In addition, this coded
message creates the same twenty
amino acids that builds all life
forms on the planet. This
similarity, according to the
theory of evolution, suggests
that all life on the planet has
evolved from a common
ancestor.