The process by which organisms with variation most suited to their environment survive and leave more offspring.
Changes in a population are due to beneficial traits or “adaptations.”
Variation of traits
Darwin studied finches of the Galapagos Islands.
The trait is beaks and the variation is in the size and shape.
Variation in a Population
Why does variation happen?
There are three main reasons why variation happens:
Mutations
Changes in DNA sequences affecting proteins.
Sexual Reproduction
Combination of different alleles creating new traits.
Gene flow
The movement of new individuals from one population to another.
Mutations
All variations come from mutations.
Some mutations can affect traits.
Some of those changes can be inherited from parents to offspring.
Sexual Reproduction
The process of creating new individuals using two parent organisms.
Requires two parents who each contribute a gamete.
Egg and sperm combine during fertilization.
Sexual reproduction can introduce new allele combinations into a population which could be good, bad or neutral.
Gene Flow
Gene flow:
The exchange of genes between populations through sexual reproduction.
Helps maintain a species.
If there was no gene flow, populations become genetically isolated.
What is a species?
Species:
A group of living organisms consisting of similar individuals which are capable of reproducing.
Must be able to mate and produce fertile offspring.
Species
Spiders might look different but if they can interbreed, they are considered the same species.
The same is true for dogs. They may not look the same, but they can interbreed, which means they are part of the same species.
Microevolution vs. Macroevolution
Changes occur throughout time which allow species to evolve.
There are two main types of evolution that occurs in species:
Microevolution
Short term changes in allele frequencies within a population or species.
Mutations and selection.
Macroevolution
Large scale evolutionary changes.
Over long periods of time such as speciation and extinction.
Speciation
The formation of new species from an existing species.
From one species to two.
Occurs when subpopulations are prevented from interbreeding.
This means the two new species CANNOT interbreed.
Requires interruption of gene flow.
The key to speciation is reproductive isolation.
Reproductive Isolation
Happens when two groups of organisms can no longer exchange genes.
This happens when:
The organisms itself changes because of random mutations
The environmental changes, causing separation of population into two or more subgroups of the original population
Causes of reproductive isolation include:
Something with a mating ritual
The time of year they mate could be off
Individuals can’t travel
Types of Speciation
Creating new species
Allopatric speciation
allo = other
patric = homeland
Species have become geographically isolated and depending on environmental factors the isolated species will change.
Sympatric speciation
sym = same
patric = homeland
Allopatric Speciation
Populations are separated by a physical or geographic barrier.
The populations evolve by adapting to different environments in the two areas.
Gene flow in the overall species is prevented, allowing new species to evolve from the original one.
Allopatric speciation
Conditions such as climate, resources, predators and competitors will differ between the two populations causing natural selection to act on and favor certain traits in each new group.
Ex. of Allopatric Speciation
Examples of causes of allopatric speciation:
River forming a new branch
Erosion forming a new valley
Organisms moving to a new area and then not being able to get back
Kaibab vs. Abert Squirrels
Allopatric speciation example - The Kaibab and abert squirrels of the Grand Canyon
They became geographically isolated from the common ancestor about 10,000 years ago
They live in opposite side of the Grand Canyon
They look similar and are related, however, they cannot reproduce viable offspring and are now considered different species
Sympatric Speciation
Speciation without physical isolation
Happens within the same space
Occurs when a reproductive barrier is created by something other than geographic isolation
Sympatric Speciation
Even though the territory that the organisms occupy is the same, they are are able to split into two different groups and become genetically different
Over time they will not be able to reproduce with one another
Sympatric speciation may be:
Temporal
Mechanical
Behavioral
Sympatric - Temporal
Temporal has to do with time
Species that breed during different times of the day, different seasons, or different years cannot mix gametes
Not able to breed, causing formation of new species
Sympatric - Mechanical
Morphological differences can prevent successful mating
Reproductive isolation
The “parts” don’t match up
Sympatric - Behavioral
Two species no longer mate because they have differences in behavioral patterns
These patterns identify members of a species
Mating rituals
Different songs from birds
Different mating dances
Adaptive Radiation
A population of one species disperses throughout an area, each finding a distinct niche or isolated habitat
Over time, there new needs and lifestyles lead to multiple speciation events originating from a single species
Artificial Selection
Nature provides the variation and humans select the variations they find useful or most important
Darwin noticed a lot of variation in traits of domesticated animals and plants that weren’t in their wild relatives
Artificial Selection and Plants
Examples of artificial selection in plants including cauliflower, cabbage, Brussels sprouts, broccoli, kohlrabi, kale all derived from Brassica oleracea (a common wild mustard) through selective breeding for different traits like terminal buds, lateral buds, flower clusters, stems and flowers, stem, and leaves.
Artificial Selection and New Species
How do you think natural selection relates to new species?