Biological Evolution

Standard B – 5.4

Standard B-5 The student will demonstrate an understanding of biological evolution and the diversity of life.

Indicator B – 5.4: Explain how genetic variability and environmental factors lead to biological evolution.

Key Concepts

•  Genetic Variability •  Genetic Equilibrium •  Speciation •  Patterns of Evolution

What You Already Know! In the 8th grade, you explained how Earth’s history had been influenced by catastrophes that affected the conditions on Earth and diversity of its life forms. You also summarized the factors, both natural and man-made that can contribute to the extinction of a species.

What You Should Understand After This Lesson

•  Genetic variation is random – Cannot be controlled in nature

•  Many factors influence genetic variability •  The Hardy-Weinberg Principle

– No genetic change – Equilibrium •  Speciation is the process of forming a new

species

Objective

•  Identify ways genetic variability can occur in a population.

•  Explain the Hardy-Weinberg Principle.

•  Explain how speciation can occur.

Vocabulary 1.  gene flow 2.  genetic drift 3.  mutations 4.  natural selection 5.  Hardy-Weinberg equilibrium 6.  gradualism 7.  punctuated equilibrium 8.  adaptive radiation 9.  divergent evolution 10.  convergent evolution 11.  coevolution 12.  extinction

Mechanisms of Evolution Natural Selection is the main mechanism of biological evolution.

–  It is not the only mechanism of evolution.

– There are many factors that can lead to biological evolution.

Factors that Affect Genetic Variability

Genetic variation is random and ensures that each new generation will result in individuals with unique genotypes and phenotypes.

– This leads to genetic variability. •  There are many factors that can lead to genetic

variability. 1.  Gene Flow 2.  Genetic Drift 3.  Non-random Mating 4.  Mutations 5.  Natural Selection

Gene Flow The movement of alleles between populations. – Occurs when

individuals join new populations and reproduce.

– Keeps neighboring populations similar.

– Low gene flow increases the chances that two populations will evolve into different species. bald eagle migration

Genetic Drift A change in allele frequencies due to chance. Causes a loss of genetic diversity. Most common in small populations.

The bottleneck effect occurs after a drastic event in the population.

Non-Random Mating

Mating has an important effect on the evolution of a population. – Males produce many

sperm continuously, making the value of each low.

– Females produce less eggs, so they are choosy about who they mate with.

–  limits the frequency of the expression of certain alleles.

Mutations •  A change in the DNA of an

organism.

•  DNA à RNA à Amino Acid à Protein

•  Increases the frequency and types of allele changes within a population.

Natural Selection •  The main mechanism to biological

evolution. – Allows for the most favorable phenotypes to

survive & be passed to future generations

Hardy-Weinberg Equilibrium Biologists use models to study populations. Provides a framework for understanding how populations evolve. Describes populations that are NOT evolving. This means the genes are staying the same. Has 5 conditions that must be met

5 Conditions of Hardy-Weinberg Equilibrium

1. The population must be very large, no genetic drift occurs.

2. There must be no movement into our out of the population.

3. There must be random mating. 4. There must be no mutations within the

gene pool. 5. There must be no natural selection.

Real Populations Real populations RARELY meet all 5 conditions of Hardy-Weinberg.

Why do you think that is? Write down 3 reasons why you think the human population would never reach genetic equilibrium.

Speciation •  The process of forming a new species by

biological evolution from a pre-existing species.

•  Can arise when species become isolated. – Populations become isolated when there is no

gene flow. –  Isolated populations adapt to their own

environments. – Genetic differences can add up over many

generations. •  Can happen in a number of ways.

Reproductive Isolation Members of different populations cannot mate successfully Final step to becoming separate species Males and females are no longer attracted to one another for a number of reasons.

Sometimes physical barriers (parts not fitting) is a reason.

Fruit flies could be attracted more to other flies

that eat the same type of fruit as they do.

Geographic Isolation

When physical barriers divide populations. Habitats being divided. A natural disaster causing organisms to split up.

A population of wild fruit flies are minding their own business eating and laying their eggs in some rotting bananas. A hurricane strikes and washes both the bananas and the flies out to see. Eventually, they land on an island just off the coast of the mainland. The fruit flies hatch and now they are completely separated from the other fruit flies on the mainland. Those on the island face a different environment than those on the mainland and eventually evolve to meet their needs on the island. Many generations go by and the island fruit flies are not different from the mainland fruit flies-they no longer mate with one another. Even if another storm were to reunite the flies, they would not mate due to their courtship evolution.

Behavioral Isolation

Includes differences in courtship or mating behaviors

Due to having different sexual selections pressures.

The mating display on the left is different from the one on the right. Even though the birds look the same to us, the females will not mate with a male if the male does not do the correct mating display.

Temporal Isolation

Timing of reproduction varies among organisms. Separation in time of mating.

Even though these two fields of flowers are near one another, they will not cross pollinate because they each bloom at different times of the year.

Environmental Factors

Many environmental factors can lead to biological evolution:

– Catastrophic Events – Climatic Changes – Continental Drift

Environmental Factors: Catastrophic Events

Environmental Factors: Climatic Changes

Environmental Factors: Continental Drift

Patterns of Evolution

There are many patterns to how evolution can occur:

1. Gradualism 2.  Punctuated equilibrium 3.  Adaptive radiation/Divergent evolution 4.  Convergent evolution 5.  Coevolution 6.  Extinction

Gradualism Gradual changes of a species in a particular way over long periods of time

Punctuated Equilibrium Periods of abrupt changes in a species after long periods of little change within the species over time.

Changes due to abrupt changes in the environment.

Adaptive Radiation / Divergent Evolution

Many species evolve from one species. Ancestor diversifies into many descendents. Descendents usually

adapted to different environments than ancestors.

Adaptive Radiation / Divergent Evolution

Evolution towards different traits in closely related species.

kit fox red fox

ancestor

Convergent Evolution

Evolution among different organisms living in similar environments. Organisms come to look like other organisms not directly related to them.

Coevolution Two or more species can evolve together through coevolution.

– evolutionary paths become connected

– species evolve in response to changes in each other

Can occur in beneficial relationships

Extinction Extinction is the elimination of a species from Earth. Background extinctions occur continuously at a very low rate.