Chapter Two Notes
Big Ideas in Biology: Change with Time
What is the significance of a change with time? How do we define evolution? What are some patterns of evolution and how can we prove that a change actually occurred. How are species formed or changed with time? These are the primary questions in chapter two.
Evolution is:
an explanation for the increase in biological diversity.
a theory that describes how current species are descendants of species of previous generations.
is a process by which populations show change (gradual or punctual) over several generations.
a basic definition of evolution is a gradual change of species with time.
First of all, a change within a species of organisms can be noted by a change in structure, habitat or even behaviour. This change can be refered to as an adaption.
When is a population of organisms considered to be adapted to it’s environment?
( this is a great question to remember..)
Even though the environment may change to a small degree, successive generations of offspring thrive.
The most desirable adaptations are those which give an organism a advantage to survive.
A way of showing a longer duration of change with time is to examine remnants of previous generations. These remnants can be actual bones or imprints of organisms. This preserved bits of structural or imprinted information are refered to as fossils.
Fossil records provide the most direct evidence of evolution
Most fossils are found in sandstone and limestone.
Problems with fossils:
There are gaps in fossil records
due to movement of the earth
no know record of organism in that time period
one organism eating another at one location and then depositing the remnant at another location
Some specimens are not complete organisms
The process of fossilization requires a specific type of soil
Some specimens are too soft to make a fossil
for example a shelled organism would make a better imprint than a worm)
With the advent of genetic research and cell biology, there are now new ways to establish indirect proof of a change with time:
Embryology:
Examining the stages of development of an embryo in a variety of species, there appears to be some similarities. This similarity was noted by …who said ” “. Basically, the development of an embryo shows the species phylogenic or family history.
2. Examining structures
There are three terms relative to structures that are useful for comparing species.
This table may be helpful for comparing homologous to analogous structures.
Structure type and example
Structure
Function
Homologous
similar
different
Analogous
different
similar
Vestigial
present
no function
Physiology
Biochemistry
Pattern of Evolutions:
Convergence
If an organisms develops similar structures due to living in similar environments but they are separated due to being geographically isolated, this is an example of convergent evolution. Basically two distinct species show a similarity, although they are not genetically link. The term converge means to come together.
Divergence
Sources of change
The concept of speciation
The term “speciation” refers to the formation of new species. New species are formed when one population of the same species is separated from another and there is no exhange of genetic information between the two populations.
what can cause speciation?
isolating mechanisms that may lead to speciation
( remember diagram in class about sea snails)
geographic
ecological
behavioral
morphology
genetic
While many of these isolation mechanisms may be crossed. For example a snail may adapt from one ecological environment to another. The one barrier that cannot not be crossed in natural situations is the reproductive or genetic barrier.
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