What is Evolution?
How did life originate on Earth? Scientists questioned this for many years to figure out how humans, and many different type of species became to be. They gathered many evidence, formulated and tested hypotheses to solve this question. The theory of evolution was accepted as – the process in which significant changes in the inheritable traits of a species occur over time. There were two major factors that contributed in the Evolutionary Theory, one being fossil records and the second being the geographic distribution of living species.
Table 1: This table is a breakdown of some of the scientists who contributed to develop the theory of evolution.
Fossil Records
As mentioned earlier, fossils are a strong evidence for formulating the theory of evolution. Fossils form through a process that alters an organism’s remains, impressions or activities by physical, biological or chemical changes and becomes a part of sedimentary rock layers. This process is known as fossilization.Baron Georges Cuvier is a scientists who studied fossils (palaeontology) which began in the 18th century. Cuvier believed in creation and did not believe that species changed over time. His evidence being that each layer contained many distinct species that were not found in the layers above or below it. Additionally, instead of believing in a single creation, he suggested that multiple events occurred at different times which made him come up with his theory of catastrophism – numerous global catastrophes in the past had repeatedly caused the extinction of species that were then replaced by newly creates forms.
Figure 1: Long after fossils form in sedimentary rock, mechanisms such as changing sea level, faults,erosion, and human excavation may bring these fossils to the surface. Retrieved from, Dulson et al. (2011)
"The Fossil Evidence for Evolution" link is a great resource for teachers to use to help students understand how scientists find evidence of evolution and piece together the history of life. The link provides an outline for two-three class periods where teachers can introduce, explain and enhance the students' knowledge about fossil evidence and how it relates back to evolution. Many multimedia resources and worksheets are available on the site.
Adaptation/Inheritance
By the 18th century, evolution began to make sense because of the fossil records. The geologist James Hutton proposed a theory called actualism – the same geological processes occurring in the present also occurred in the past. Then came Sir Charles Lyell which added his principles of uniformitarianism – Earth’s surface has always changed and continues to change through similar, uniform, and very gradual processes.
However, the one scientists who recognized that the environment played a key role in evolution was Jean Baptiste Pierre Antoine de Monet, Chevalier de Lamarck. He believed that species adapted to changing environmental conditions in order to survive long periods of times. He also hypothesized the inheritance of acquired traits and was famous for his giraffe example. If a giraffe stretched its neck for leaves, over time the process of their neck elongating would get inherited by several generations.
Figure 2: Lamarck believed that the long necks of giraffes evolved as generations of giraffes reached for ever higher leaves.
*Watch this animation of chameleons on how their traits and adaptations helps it to survive.
Video Retrievedfrom: https://www.youtube.com/watch?v=-IiP-9VzY9w
Charles Darwin
Darwin was an English naturalist and geologist who is best known for his contributions to evolutionary theory. He went on a voyage that lasted almost five years on the HSM Beagle.
* To learn more about Darwin watch the video below.
Video Retrieved from: https://www.youtube.com/watch?v=pQp2lFcDEbw
One of Darwin’s stop was at the Galapagos Islands, where he became very interested in studying one of the species there- the finches. He collected a few of them and noticed distinct variation from island to island such as the finches having different beaks. Darwin began to wonder why continents separated by large distances would have entirely different species occupying similar ecological niches. The finches helped Darwin to solidify his idea of natural selection. He concluded that their beaks had adapted to the type of food they ate in order to fill different niches on the Galapagos Islands. Their isolation on the islands over long periods of time made them undergo speciation.
Beak of the Finches Activity
Try this "Beak of the Finches" activity in your class so students can gain a better understanding though this demonstration of how different adaptations help different birds in collecting different types of food.
Brief Description: Students receive a tool which is used to represent a bird's beak. Students will collect as much "food" as they can in a 30 second period. Students will analyze their findings and compare how "birds" with different "beak adaptation" are better at collecting different types of seeds.
Figure 3: The finches that were collected from the Galapagos Islands by Darwin and sent to Ornithologist John Gould. The different beaks indicates the distinction between species.
Beak of finches activity
Evidence of Evolution
A scientific theory is an idea that explains a natural phenomenon or group of facts and is repeatedly confirmed through experimentation or observation. The theory of evolution has a lot of evidence to confirm it. Below found some evidence that proves this theory.
1- Evidence from Anatomy
Homologous Features
Structures that are similar in their morphology, anatomy, genetics and embryology but dissimilar in their functions. These homologous features are inherited from a common ancestor. For example they have similar developmental pattern in the embryos, they have same type of bones, organs, muscles etc.
Figure 3: The forelimbs of these organisms are each adapted to carry out verydifferent functions, yet they all pos-sess very similar bone structure.
Analagous Features
Structures that are similar in function but not in origin or anatomical structure. For example, animals that belong to different groups may all live in the same type of habitat/environment. This can lead to the animals having similar type of life. As shown in Figure 4, the analagous features of the wings of insects, pterodactyl, birds and bats are meant for flying, however their internal structure is not the same.
Figure 4: The wings of these organisms all serve the same function however they all differ in their anatomical structures.
Vestigial Features
Structure that no longer seems to have a purpose in the current form of an organism. These vestigial features were organs that performed an important function in the organism at one point in the past. Eventually, these structures become less and less important as a population changes through natural selection. For example, humans have muscles for moving their ears but not everyone can make use of these muscles. Figure 5 shows other examples of vestigial structures
Figure 5: Dogs have a vestigial toe. Althoughthe bones remain, this digit servesno present purpose. Pigs’ feet havetwo well-developed digits; the othersare vestigial. The horse has only oneenlarged digit; the others are ves-tigial or have been lost entirely.
2- Evidence from Embryology
Embryology is the study of the early pre-birth stages of an organism’s development. Embryology has been used to determine relationships between different organisms. For example, all vertebrates have similar stages of early embryo development because all vertebrates have a common ancestor. In figure 6, homologous features such as tailbones are present in each of these embryos.
Figure 6: These different organisms show similarity in the early stages of their embryo, however differentiation begins to show in the later stages of development.
Evidence for Evolution Dry Lab
This lab activity is designed to enhance the students' understanding on the different types of evidence found that determined the theory of evolution. The purpose is to learn about homologous, analogous, vestigial structures, fossils, and embryology and their significance in evolution theory. There are two documents for this activity. One being the outline of the lab which is divided into section; evidence from anatomy, embryology, and fossil records. The second document being the worksheet where students will answer questions that corresponds to the activities found on the lab document.
Evidence For Evolution Lab Activity Outline
Evidence For Evolution Worksheet lab activity
**NOTE: This lab can be truned into a Jigsaw activity where the students are divided into groups and focus just on one type of evidence. Students then complete their part within their expert groups, then regroup into their home groups to explain their typpe of evidence
Obtained from: http://smshs.enschool.org/ourpages/auto/2015/10/18/42604318/Day%203%20_%20BIO%20Evidence%20for%20Evolution%20Activity.pdf
Natural Selection Vs Artificial Selection
Both natural selection and artificial selection refer to the processes that change traits in living species from one generation to the next. However, natural selection is the process where a population's environment acts on that population such that well-adapted individuals thrive while poorly adapted individuals die out. On the other hand, artificial selection happens when people take the place of natural processes and breed plants or animals for particular traits.
* Watch this video as it explains the difference between natural and artificial selection through different examples.
The Peppered Moth Simulation Activity
This activity is designed to illustarte the principles of natural selection and variation within a species of the peppered moths in regards of colour: light gray, medium gray, and dark gray. The various coloured sheets of paper will represent the changing environment and the moths will be represented through the paper dots (created with the hole punch). The document addresses the overall and specific expectations along with the students learning goals and assessment startegies. It also includes teacher's notes, additiontional tips, instructions and assessments (questions). This activity is designed to be done in a 75 minute class period.
Peppered Moth Activity
Obtained from: https://evolution-resource-binder.wikispaces.com/file/view/The+Peppered+Moth+Simulation+Activity+Teachers+Notes.pdf
Artificially Selecting Dogs Activity
The purpose of this activity is for students to grasp the idea of artificial selection through the development of new dog breeds with characteristics that make the dogs capable of performing a desirable task. This activity is designed to be done in an hour period.
* Click on the link below to view the full activity.
Mechanisms
Natural Selection isn't the only process where a population changes over time. In fact there are many other types of mechanisms involved that causes populations to evolve. Below found some of the mechanisms that play a crutial component of evolutions.
1- Mutation
Mutation is one type of mechanisms that plays a key role in the process of evolution. A mutation is a change in DNA which affects how an organism looks, behaves, and its physiology. Mutations are the raw material of genetic variation; so without it evolution could not occur.
* Watch this video to gain a better understanding of mutation and its correlation with evolution
*Watch this video to gain a deeper understanding of how genetic variation plays an important role within the same population and how it leads to creating new species.
3- Genetic Drift
Gene Frequencies in a population changes randomly over time through genetic drift. The frequency of an allele within a population changes by random chance as a result of sampling error from generation to generation. The effects of genetic drift are much easier to see in small populations compared to large ones. Random drift is caused by recurring small population sizes, severe reduction in a population size known as "bottlenecks", and founder events where a new population starts from a small number of individuals.
2- Genetic Variation
Genetic variation is the diversity in gene frequencies which is why individuals of a species have similar characteristics but they are rarely identical due to the variation in the DNA sequence. Having variations allows for flexibility and survival of a population during changing environmental circumstances. Genetic variation is often an advanatge since it is a form of preparation for the "unexpected".
* Watch this video as it shows the importance of large population size in neutralizing random change through a population genetics simulator.