Evolution:
The gradual changing of organisms over time
The Galapagos Islands
Below is the video that we watched in class, which explains how Charles Darwin developed his theory of Evolution.
*If you were absent the day we watched this in class, it is highly recommended that you watch it (you only need to watch the first 45 minutes).
*If you were absent the day we watched this in class, it is highly recommended that you watch it (you only need to watch the first 45 minutes).
Below is another great documentary on Evolution. In this, you can get a glimpse of the diversity of species on the Galapagos Islands, as well as how those animals inspired Charles Darwin to come up with his theory of Evolution.
Natural Selection
Darwin proposed the idea that natural selection was what caused a species to evolve. Natural selection is the process by which individuals that are better adapted to their environment are more likely to survive and reproduce than other members of the same species. It is often referred to as "survival of the fittest". Natural selection is what Darwin believed was responsible for evolution.
Evolution and natural selection interactives
Play this game to give you an idea of how natural selection works to change a species. Remember, when a species changes over time this is called evolution.
Go to this interactive website to see how environmental changes can affect the evolution of a species.
How Darwin's Theory of Evolution (and natural selection) would explain the long necks in giraffes:
Evidence of Evolution
Homologous structures
As evidence that two or more species evolved from a common ancestor, scientists point to the presence of homologous structures in different species. Homologous structures are similar structures that related species have inherited from a common ancestor.
Look at the homologous structures below. Although these are all different species, they share similar bones/bone structure. This is evidence that these animals evolved from a the same species (a common ancestor).
Look at the homologous structures below. Although these are all different species, they share similar bones/bone structure. This is evidence that these animals evolved from a the same species (a common ancestor).
Similar embryos
When organisms have embryos that are similar, it provides more evidence that those organisms have a common ancestor (meaning, that they both evolved from the same species).
Remember, an embryo is a developing organism (after it is fertilized) but before it has fully formed. It is made in the early stages of development, after the egg has been fertilized.
Remember, an embryo is a developing organism (after it is fertilized) but before it has fully formed. It is made in the early stages of development, after the egg has been fertilized.
Similarities in DNA (and protein structure)
DNA evidence is a relatively new type of evidence used to support the theory of evolution. The more similar two species' DNA is, the more closely they are related. Similarly, the more closely the sequence of their amino acids are (which make up proteins), the more closely the species are related.
Scientists have used DNA evidence to show what they had already suspected - that humans are most similar to chimpanzees. They came to this conclusion because human DNA is almost 99% the same has chimpanzee DNA.
Below is a section of DNA from a human, and the same section of DNA from a chimpanzee. Look at how many similarities there are in the nitrogen bases (the A's, T's, G's and C's).
Scientists have used DNA evidence to show what they had already suspected - that humans are most similar to chimpanzees. They came to this conclusion because human DNA is almost 99% the same has chimpanzee DNA.
Below is a section of DNA from a human, and the same section of DNA from a chimpanzee. Look at how many similarities there are in the nitrogen bases (the A's, T's, G's and C's).
Fossils
Fossils can show how one species has changed over time. They provide a way for scientists to see what a certain species was like millions of years ago. They can compare that to the structure of that species today.
Look at the picture below. It shows how the modern horse has evolved from a species that had similar bone structure, but was much smaller.
Look at the picture below. It shows how the modern horse has evolved from a species that had similar bone structure, but was much smaller.
Fossils can also give us evidence about WHEN a certain species existed, and when they might have gone extinct.
Look at the layer of rock below. The layers were formed by sediments covering dead organisms. Over time, the sediments turned in to sedimentary rock, leaving behind evidence that an organism once existed there.
The fossils at the bottom (layer D) are the oldest fossils, so scientists know that organism evolved first and has been around the longest. The fossil on the top layer (layer A) is the newest fossil, so scientists know that organism evolved the last.
This is called relative dating. It cannot be used to give the specific age of a fossil, but it can be used to compare the fossils to see the order in which species existed.
This is called relative dating. It cannot be used to give the specific age of a fossil, but it can be used to compare the fossils to see the order in which species existed.
How to scientists show these evolutionary relationships?
…Through branching trees. A Branching tree is a diagram that shows how scientists think different species are related.
Some things that we can learn from this branching tree:
- All of these animals evolved from a common ancestor
- The lemur was the first species (of these five species) to evolve.
- The chimpanzee was the last species (of these five species) to evolve.
- The spider monkey evolved after the lemur, but before the baboon.
- The gorilla is more similar to the baboon and the chimpanzee than it is to the lemur or the spider monkey.