unit 3 evolution and biodiversity. what explains how life has changed over time? according to...
TRANSCRIPT
What explains how life has changed over time?
According to scientific evidence the major force of adaptation to changes in environmental conditions is biological evolution
Charles Darwin and Alfred Wallace proposed the concept of natural selection as the mechanism for biological evolution
Natural Selection and Evolution
Biological evolution by natural selection involves the change in a population’s genetic makeup through successive generations.
Three conditions are necessary for biological evolution:Genetic variabilityTrait must be heritableTrait must lead to differential reproduction. (More
viable offspring)
Gene Pools• Genetic variation may
arise through micro-evolution of a population’s gene pool.
• The gene pool consists of all the alleles (Copies of genes) in all the individuals making up a population which acts as the reservoir from which the next generation draws its genes
Mechanisms of Microevolution• There are four processes that can change the
composition of a gene pool– Mutation (change in DNA)– Natural Selection (3 major types)– Gene flow (immigration, emmigration)– Genetic Drift
Mutation• Random changes in the genetic structure or
number of DNA molecules in a cell is the ultimate source of genetic variability in a population.
Natural Selection• When some individuals of a population have
genetically based traits that cause them to survive and produce more offspring than other individuals
• There are three types of selection that will shift a populations gene frequencies.– Directional– Disruptive– Stabilizing
Three Types of Selection• Directional-Changes in the environment cause
allele frequencies to shift so that individuals with traits at one end of the normal range become more common
Three Types of Selection• Disruptive-Environmental conditions favor the
individuals at the extreme ends of genetic spectrum
Genetic Drift• Another way gene pools can change is due to
genetic drift• Genetic drift is the change of a small population
due to chance not specific selection• Two situations can shrink populations down to a
size where genetic drift has a greater impact– Bottleneck Effect-Disasters, such as earthquakes,
floods, droughts and fires reduce the size of a population
– The Founder effect- When a few individuals colonize an isolated island, lake, or some new habitat
Limits on Adaptation through Natural Selection
A population’s ability to adapt to new environmental conditions through natural selection is limited by its gene pool and how fast it can reproduce.Humans have a relatively slow generation time
(decades) and output (# of young) versus some other species.
Common Myths about Evolution through Natural Selection
Evolution through natural selection is about the most descendants.Organisms do not develop certain traits because they
need them.There is no such thing as genetic perfection.
Biodiversity• One important renewable resource is
biodiversity: The different life forms and life sustaining processes
• Biodiversity has four main components– Species Diversity– Genetic Diversity– Ecological Diversity– Functional Diversity
Functional Diversity• The biological and chemical processes such as
energy flow and matter recycling needed for the survival of living things.
Why Should We Care About Biodiversity?
• Biodiversity provides us with:–Natural Resources (food water, wood,
energy, and medicines)–Natural Services (air and water
purification, soil fertility, waste disposal, pest control)
–Aesthetic pleasure