4 Natural Selection and Evolution

Evolution Big Ideas and Big Questions 

Big Ideas 

  • There are similarities and differences we can observe across species.
  • We can make predictions about how populations can change over time.
  • Variations in traits can result in organisms’ ability to reproduce.
  • Natural selection leads to predominance of particular traits in a given population; likewise, some traits can be suppressed.
  • Scientists utilize the fossil record to document the existence, diversity, extinction, and changes of many life forms throughout history.

Big Questions 

  • How did we end up with the diversity of organisms that we currently have on our planet?  What evidence do we have to help us answer this question?
  • Why do organisms have so many similarities, yet so many differences?
  • How do organisms get their traits?
  • What makes a bird, a bird?


Evolution Overview

All living things evolve. Evolution is a permanent change in genetic makeup of a population over time. A population is the number of all organisms of the same species who live in a particular area and are able to interbreed. Evolution does not happen overnight, but over time and across many generations. It can be caused by natural selection, mutation, or other selective factors. Evolution will be further discussed below.

Evolution and genetics go hand in hand. The reflection of adaptations organisms have made to changing environments can result in genetic variations. and evolution This genetic information enables some individuals to adapt and survive the changing environment while others may not. Mutation, adaptation, and phenotypes help us understand evolution more.

History of Evolution

In the 19th century, Sean Baptist De Lamarck introduced the first theory of evolution, called acquired inheritance. This early theory stated that traits acquired during an organism’s lifetime would be passed down to their offspring. Lamarck’s most common example is the evolution of the giraffe neck. He thought the giraffes had short necked ancestors and would stretch their necks to reach leaves. The giraffes’ were struggling to eat the leaves and because they had been stretching and reaching for them, the longer neck was passed along to the offspring. Of course this is incorrect because we know that traits developed over a lifetime are not automatically passed on to offspring.

Today, acquired inheritance is NOT at all an acceptable scientific theory. But it is important to acknowledge where evolution analysis began. This brings us to Charles Darwin and his theory of evolution. Darwin observed that organisms have variations based on their environment. Darwin visited the Galapagos islands where he observed wildlife as well as collected samples and brought them back to his home in England for further research. Some of his data and analysis was centered around the Galapagos finches. He noticed that from island to island the birds looked the same but the beaks were slightly different. Some of the birds had bigger, sharp beaks while others were small. This was related to a variety in diet for the finches. The birds with the bigger beaks were able to eat harder substances, like nuts, while the smaller beaked birds fed on small, soft seeds or fruit. The variations gave certain Galapagos finches advantages in specific areas.  For example, birds with bigger beaks were able to survive better in locations where the food sources were harder substances. These seemingly minor variations provided advantages to some members of the population over others.  This helped Darwin began to realize the different drivers for biological evolution. Thus, the theory of evolution was born.

History of Evolution 

To learn more explore more about the history of evolution watch this video.

Drivers for Biological Evolution

We define evolution as the change in the allelic frequency in a population over time. This is a change in heritable characteristics that happens over many generations of a population. There are many factors that drive evolution and can cause it to happen. The drivers for these biological changes are:

  • Natural selection
  • Mating preference
  • Migration
  • Mutation

Natural Selection

Natural selection is the process in which certain varieties of inheritable traits are more reproductively successful than other varieties. Organisms with more favorable traits are more likely to survive and produce offspring. Natural selection varies in reproduction, heredity, physical characteristics and number of offspring. A good way to think about it is “survival of the fittest”. Those who are well adapted continue to pass those traits along for generations so that specific populations can continue to thrive. Over time, the process of genetic change can result in new genes, traits, and species all because of changes in the genetic code or DNA. This mechanism can then result in natural selection because only the adaptive and strong species can survive.

   Teacher Time Out: Natural Selection

How does this connect to the NGSS Progression

DCI: LS4.B Natural Selection: In third through fifth grade students learned that sometimes the differences in characteristics of the same species provide advantages in a variety of areas. Students are introduced to survival, finding meats, and reproduction. Those building blocks then help students throughout middle school examine natural selection and the traits determined by genes which are then passed to offspring.

             K-2                       3-5                               6-8
LS4.B Natural Selection N/A Differences in characteristics between individuals of the same species provide advantages in surviving and reproducing. Both natural and artificial selection result from certain traits giving some individuals an advantage in surviving and reproducing, leading to predominance of certain traits in a population.


Implementation into the Classroom

Formative Assessment – Habitat, by Paige Keely

1. Identify held beliefs of your students about what happens to a fictional organisim when there is a sudden shift in the habitat.


2. Living or Dying: Beans

An investigation lesson where students use a model to observe the change in phenotypes overtime within a species.

3. Preying on Beans – Evolution 101


4. Rock Pocket Mouse – BioInteractives

This video supports a card sort activity which requires middle school students to apply understanding of natural selection, specifically changes in fur color over time.

Mating Preference

Everybody wants to choose the best mate but what makes a mate the “best”? Mating preferences, or sexual selection, is seen in sexual organisms. But the way in which an organism chooses a mate differs. Every organism wants to receive the “good” genes. This sexual selection creates a situation in which certain inheritable morphological or physical traits provide greater potential for mating and therefore, greater chance of passing your genes to the next generation.


Migration is the movement of some members of a population either into or out of an existing population. One purpose of migration is to move to a new location, meet a new population of the same species and breed with them. Species migrate so they are able to take full advantage of more favorable conditions as well. Migration is frequently occurring for many organisms on a seasonal basis as well as a daily basis. These movements happen to take advantage of food availability, safety from predators, mating opportunity, and other environmental factors. Each organism migrates in its own way. Human beings migrate for economic, social, political, and environmental reasons while other organisms migrate mostly for environmental factors. The most common reason for migration in organisms other than humans is due to seasonal changes. Birds migrate south for the winter due to the cold weather (hence the term snowbirds referring to humans heading south for the cold months). Other species, such as whales, undertake the longest migration of any mammal from their feeding grounds in the arctic waters to breed in the Baja lagoons. This movement of the population is a potential driver for biological evolution. Migration enables a gene flow to occur. Gene flow is the movement from one population to another. During this time gene pool frequencies are easily changed, resulting in evolution.


Mutations are changes in genetic sequencing. Evolution and mutation go hand in hand.  Mutations are important to evolution. Even more so, every single genetic feature of every organism was initially the result of a mutation. Mutations occur when there is a change in the DNA sequence that may or may not result in new traits. Mutations create the new DNA sequence for a particular gene thus creating a new allele. These mutations can be caused by mutagens (environmental factors including radiation, chemicals, and infectious agents) or errors within DNA replication, transcription, or translation. Mutation may sound like a scary or bad thing, but mutational effects can be beneficial, harmful, or neutral.




HIV resistance

Trichromatic vision (ability to discriminate between the colors red, green, and blue


Cystic fibrosis

Eye color

Hair color



Want to learn more? Check out this cool article about gene therapy. Scientists were actually able to make monkeys have colored vision (trichromatic vision).


Evidence for Evolution

Science utilizes the structure of claims based on evidence, and as more data is found concepts change or alter to represent the new information. The scientific concept of evolution is no exception to this. In this section you will observe a variety of evidence for the theory of evolution. While diving into this section keep in mind that evolution is a change in allelic frequency within a population overtime. In many instances we can observe the change in alleles through the phenotypes that are represented by them. As you make your way through this section consider how the evidence shown may support and to what extent the evidence may support the theory of evolution.

        Teacher Time Out: Evolution and Diversity

How does this connect to the NGSS Progression

DCI: LS4.A Evidence of Common Ancestry and Diversity: Once students are in third grade, they begin to learn about plants and animals that once lived but are no longer here and how fossils provide evidence. The middle school students further their investigation of fossils and begin to compare the similarities and differences between living organisms today and organisms in the fossil record.

            K-2                       3-5                               6-8
LS4.A Evidence of common ancestry and diversity N/A Some living organisms resemble organisms that once lived on Earth. Fossils provide evidence about the types of organisms and environments that existed long ago. Species can change over time in response to changes in environmental conditions through adaptation by natural selection acting over generations. Traits that support successful survival and reproduction in the new environment become more common.


Implementation into the Classroom

  • Similar or Different- Show students images of organisms that live in the same ecosystems. Ask students what they notice that is similar and different between the organisms. Have students create arguments about how the organisms are related.
  • Evolution Lab- students can explore the tree of life and how organism DNA is similar and different in this PBS interactive.
  • For additional classroom activities, explore Evolution 101 website – https://evolution.berkeley.edu/evolution-101/
  • For additional understanding of the nature of science and classroom applications, explore Understanding Science website – https://undsci.berkeley.edu/

Consider this video depicting the relationship between dinosaurs and birds.




Fossils are important evidence for evolution because they show that life on earth once looked different than it does now. Fossils are physical proof of the existence of now-extinct animals that lived on earth during different times. Fossils of the most simple organisms can be found in the oldest of rocks. Darwin’s theory supports the idea that these simple organisms gradually evolved into more complex organisms.

Fossils support Darwin’s theory because they provide a snapshot in time of the past, allowing us to study how an organism has changed as life developed on earth.

                                  Homologous structures

                 Analogous structures

These structures are structures that are similar in a related organism because they were inherited from a common ancestor. They are considered homologous structures because these organisms have similar underlying anatomy but are used for different functions.

Examples: the arm of a human, wing of a bat or bird, leg of a dog, flipper of a dolphin or whale.


(Cerezo, 2015)


(Marks, 2019)

These structures are structures that are similar in unrelated organisms.

Examples: wings of an insect, bird, and bat. All of these organisms have the ability of flight but developed independently because of the common function of flying.


(mrtangextrahelp Seguir, 2013)







   Teacher Time Out: Evolution and Evidence

How does this connect to the NGSS Progression

DCI: LS4.C Adaptation: Students discuss that for any particular environment there will be some organisms that survive, some that thrive, and some that do not. This adaptation by natural selection is then explored throughout middle school (6-8) and students take a look at generations and the change over time in response to changes in the environment.

       K-2        3-5                                                          6-8
LS4.C: Adaptation Living things can survive only where their needs are met. If some places are too hot or too cold or have too little water or food, plants and animals may not be able to live there. Particular organisms can only survive in particular environments.


Populations of organisms live in a variety of habitats. Change in those habitats affects the organisms living there.

The fossil record documents the existence, diversity, extinction, and change of many life forms and their environments through Earth’s history. The fossil record and comparisons of anatomical similarities between organisms enables the inference of lines of evolutionary descent.


Implementation into the Classroom

  • Fossil Bags- Using bags with bone parts students act as archeologists and pull only a few bones from the bag. Students work to make a claim based with evidence to determine what the animal may be.
  • Trash Excavation- students gather items from a recycling bin and determine the age of the item. They make claims backed with evidence to explain the age of items and what items may have been for.


Embryology is the study of the development of embryos. Studying embryos helps us look at the similarities between early stages of an embryo among different species. Ernest Haeckel came up with some exaggerated drawings (figure 35) to show the similarities and differences. Though they are not truly accurate, they were some of the first attempts at using embryology as evidence for evolution. This picture is often questioned but we must acknowledge the similarities. Insects and people born with uteruses both have eggs. Plants have both a sperm (pollen in plants) and an egg like humans. Most vertebrates have a spine. We can see the similarities within these species even though they are different.


Figure 35: Embryology Development of Organisms

Image: Marks PPT


Watch this short embryology video.

DNA Sequencing

DNA sequencing is the process of determining the order of nucleotides within DNA to compare healthy DNA to the mutated DNA or to observe connections between species. DNA contains an enormous amount of genetic information about the evolution of each organism. DNA sequences form hereditary links between generations. Thus, scientists want to study the relationship between DNA and evolution. By studying DNA sequencing, evolutionary origins can be unlocked and compared. This helps scientists determine evolutionary relationships among organisms and is able to indicate when this divergence from the origin happened in the past.

Review Concepts

  • Some kinds of plants and animals that once lived on Earth are no longer found anywhere.
  • Fossils provide evidence about the types of organisms that lived long ago and also about the nature of their environments.
  • Anatomical similarities and differences between various organisms living today and between them and organisms in the fossil record, enable the reconstruction of evolutionary history and the inference of lines of evolutionary descent.
  • For any particular environment, some kinds of organisms survive well, some survive less well, and some cannot survive at all.
  • Adaptation by natural selection acting over generations is one important process by which species change over time in response to changes in environmental conditions.
  • Traits that support successful survival and reproduction in the new environment become more common; those that do not become less common. Thus, the distribution of traits in a population changes.
  • Sometimes the differences in characteristics between individuals of the same species provide advantages in surviving, finding mates, and reproducing.
  • Natural selection leads to the predominance of certain traits in a population, and the suppression of others.
  • Populations live in a variety of habitats, and change in those habitats affects the organisms living there.
  • Changes in biodiversity can influence humans’ resources, such as food, energy, and medicines, as well as ecosystem services that humans rely on

*Review Concepts are taken directly from the elementary and middle level NGSS Disciplinary Core Ideas (LS4)

Practice Quiz – Natural Selection & Evolution

Click on this link to check your understanding.




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