1. Other Mechanisms of Change
Theory of Evolution
Other Mechanisms of Change

2. What are we learning today?
Benchmarks
SC.912.L – Describe the conditions required for natural selection, including: overproduction of offspring, inherited variation, and the struggle to survive, which result in differential reproductive success.
SC.912.L – Describe how mutation and genetic recombination increase genetic variation.
SC.912.L – Discuss mechanisms of evolutionary change other than natural selection, such as genetic drift and gene flow.
Learning Objectives
I will explain and describe how mutation and genetic recombination increase genetic variation.
I will explain and describe the scientific mechanisms, such as genetic drift, gene flow, and nonrandom mating, resulting in evolutionary change.

3. What are other mechanisms of evolution?
Evolution is the change in a population’s genetic material over generations.
Four other mechanisms of evolutionary change exist besides natural selection.
Mutations
Gene flow
Genetic drift
Nonrandom mating

4. What are mutations?
A mutation is a change in the genetic material of a cell.
Mutations affect evolution by producing totally new alleles.
Germ mutations occur in the reproductive cells, or gametes, of an individual.
These mutations can be passed on to the offspring.
They can affect the survival of an individual organism or a genetic line of organisms.
Mutations that keep the lactase gene permanently switched on are common among modern Europeans — but not among their ancestors. In March 2007, a team of German and British researchers announced that they went looking for that mutation in the 7000-year-old fossils of ancient Europeans and came up empty-handed. The researchers managed to extract the length of DNA corresponding to the lactose tolerance mutation from eight Neolithic human fossils and one Mesolithic fossil, but those DNA sequences did not carry the telltale mutation. The results suggest that as late as 5000 BC most ancient Europeans could not have digested milk as adults — and that they only later evolved into milk-drinking societies.
Today, the ability to digest milk as an adult seems like a clear benefit, but that wasn't always the case. Lactose tolerance is only advantageous in environments and cultures where humans have access to domesticated dairy animals. Multiple lines of evidence from human genetics, cattle genetics, and archaeological records suggest that Middle Eastern and North Africans populations domesticated cattle between 7500 and 9000 years ago, and that these animals were later brought into Europe. In that cow-friendly environment, being able to drink milk directly (instead of having to process it into lower-lactose cheese) would have been advantageous, providing additional sustenance and, during droughts, a source of water. The lactose tolerance mutation arose randomly (as all mutations do), but once it arose, it had a distinct advantage in these populations. Natural selection would have favored individuals carrying the lactose tolerance mutation, spreading it through ancient European populations that depended on dairying. Many thousands of years later, we see the indirect (but delicious) effects of this mutation's success in European cuisines: oozing French cheeses, Swiss milk chocolate, and creamy Italian gelatos.
Surprisingly, with respect to dairying, human populations on separate continents seem to have led parallel lives — or rather, followed parallel evolutionary trajectories. Recent evidence suggests that cattle may have been domesticated independently in several places, including Africa. As African populations began herding cattle, lactose tolerance became an advantageous trait. The stage was set, in Africa too, for the spread of a lactose tolerance mutation. In January 2007, an international team of researchers led by geneticist Sarah Tishkoff announced that they had uncovered the genetic roots of Africans' lactose tolerance. Just as in Europe, on this continent, mutations (in this case, probably three) randomly arose, and these happened to have the effect of keeping the lactase gene switched on. And just as in Europe, these mutations were favored by natural selection and quickly spread through dairy-dependent populations.

5. What are mutations? Mutations can be: Neutral- No affect
No pattern of increase or decrease in allele frequency
Harmful
Usually naturally selected against and rid of in short time
Beneficial
usually increase over time
A snake with two heads, each able to think and eat separately and even steal food from each other, has become a popular attraction at a Ukrainian zoo.
The small albino California Kingsnake, now on show in the Black Sea resort of Yalta is quite a handful, zoo workers told AFP.
The snake's two heads are fiercely independent, are not always in agreement and like to snatch food from each other, said keepers of the private zoo, called Skazka, or Fairy Tale.
"Sometimes one head wants to crawl in one direction and the other head in another direction," zoo director Oleg Zubkov told AFP.
Zoo worker Ruslan Yakovenko added that he tries to feed the snake's two heads separately as they sometimes fight for food.
"If it is really hungry, its heads may steal food from each other," he said, adding he also needs to separate the heads with a barrier.

6. What is gene flow?
Gene flow is the process of genes moving from one population to another.
Gene flow can occur through
Immigration ( the movement of individuals into a population)
Emigration (the movement of individuals out of a population)
The Migration of Genes – Gene Flow Migration is the movement of populations, groups or individuals. In genetic terms, migration enables gene flow: the movement of genes from one population into another. If the two populations originally had different gene frequencies and if selection is not operating, migration (or, to be exact, gene flow) alone will rapidly cause the gene frequencies of the different populations to converge.
Migration will generally unify gene frequencies among populations rapidly in evolutionary time. In the absence of selection, migration is a strong force for equalizing the gene frequencies of subpopulations in a species. Provided that the migration rate is greater than zero, gene frequencies will eventually equalize. Even if there is only one successful migrant per generation, gene flow inevitably draws the population's gene frequency to the species' average. Gene flow thus acts to bind the species together.

7. What is genetic drift?
Genetic drift is the process by which alleles frequencies in a population change as a result of random events, or chance.
It can result in substantial changes within a population.
Only significant in small and medium-sized populations.
Genetic drift simulation and 5-item quiz:

8. What is nonrandom mating?
Nonrandom mating occurs whenever individuals may choose partners.
Influenced by geographic proximity and assortative mating
Sexual selection occurs when certain traits increase an individual’s success at mating.

9. We have discussed how evolution by natural selection works
Review
We have discussed how evolution by natural selection works
NATURAL SELECTION requires:
Overproduction of offspring
Inherited Variation
Struggle to survive
Differential Reproduction
We have discussed several ways natural selection can act on populations
*Genetic drift
Gene flow
Mutations
Non-random mating
You should be able to explain/describe each of these concepts by now

10. Lets go over genetic drift again
Genetic Drift is a RANDOM change in allele frequencies in a population due to a completely random event
2 types of Genetic Drift Situations:
Bottleneck effect
Founder’s effect

11. Genetic Drift: Bottleneck Effect
Sometimes a random disaster may kill many individuals in a population.
Those alleles left may not be the same representation as the original population

12. Genetic Drift: Founder’s Effect
Migration of a small subgroup from a main population leads to a difference in allele frequencies from the original population’s
The founding population will reproduce and pass on the alleles of the founders

13. Rates of evolution: Punctuated Equilibrium vs Gradualism
Small changes occurring little by little
Usually hard to notice over short period of time
Change is slow, constant, and consistent
Punctuated Equilibrium
Change occurs in spurts
Period of little change, followed by period of huge change
Change is noticeable and abrupt
Punctuated Equilibrium
Gradualism

14. 3 Types of Natural Selection
Directional Selection
Better “fitness” toward 1 direction
Example: bigger the beak, the better fit
Stabilizing Selection
The intermediate trait is best fit
Example: the grey species is better fit than the white or black
Disruptive Selection
the extreme, or outer end traits are better fit than the intermediate trait
Example: the white and black species is better fit than the grey species

15. 3 TYPES OF SELECTION

16. MICROEVOLUTION VS MACROEVOLUTION
Microevolution is evolution based on the genetic level
Genetic drift
Mutation
Nonrandom mating
Gene flow
Macroevolution is evolution based on more visually observable changes in species
Extinction
Speciation
Adaptive radiation
Convergent Evolution
Co-evolution

17. Extinction and Speciation
Extinction is when a species disappears forever from the earth as a result to its population being completely diminished
Speciation is the formation of new species from already existing species
But how do new species form?
 Geographic isolation
Temporal isolation
 Behavioral isolation
Reproductive isolation New Species

18. Reproductive Barriers
PRE- Reproductive Barriers
Habitat Isolation
Geographic isolation
Temporal isolation
Mechanical isolation
Behavioral isolation
Gametic (reproductive) islation
POST- Reproductive Barriers
Hybrid Sterility
Reduced Hybrid Viability

19. Adaptive Radiation
A single species evolves over a relatively short period of time into several forms that live in different ways Galapagos finches evolved different beaks and behaviors that allow them to eat different kinds of food

20. Convergent Evolution
When distantly, unrelated species LOOK similar because they have evolved in similar environments

21. The evolution of one species drives the evolution of the other
Co-evolution
Sometimes 2 different species live and interact so closely together, they evolve together
The evolution of one species drives the evolution of the other
EXAMPLE:
Flowers and pollinators