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12/1/2025
AP Biology
7.8 Phylogeny
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Understanding Phylogeny
Phylogeny is the study of evolutionary relationships between organisms. Scientists use phylogenetic trees to visualize these relationships, showing how species are connected through their evolutionary history. These tree-like diagrams help us see which species share recent common ancestors.
When you look at a phylogenetic tree, each branch point represents an ancestor from which different species evolved. The diagram helps scientists organize life based on evolutionary history rather than just physical appearance.
The concept of phylogeny is based on the fundamental idea that all living organisms on Earth share a common ancestor if you go back far enough in time.
Quick Tip: When examining a phylogenetic tree, focus on the branching patterns rather than the physical distance between species on the diagram – the pattern shows relatedness, not physical similarity.
Common Ancestry and Classification
All living organisms share a common ancestor - a powerful idea that forms the foundation of evolutionary theory. Species change over time through a process called descent with modification, which explains how different species evolve from shared ancestors.
Scientists use a hierarchical classification system to organize living things based on their evolutionary relationships. This system moves from broad to specific categories: domain, kingdom, phylum, class, order, family, genus, and species. The more categories two organisms share, the more closely related they are.
Homologous structures provide important evidence for evolutionary relationships. These are body parts that have similar underlying structure and development but might serve different functions. For example, a human arm, bat wing, and whale flipper all have the same basic bone arrangement despite their different uses.
Remember This: Taxonomy (how we classify organisms) is constantly being revised as we learn more about evolutionary relationships through new scientific discoveries.
Evidence for Evolutionary Relationships
Analogous structures look similar and perform similar functions but evolved independently. Unlike homologous structures, they don't indicate shared ancestry. Think of bird wings and butterfly wings - both for flying but with completely different origins and structures.
Comparing molecular homology - similarities in DNA, RNA, and protein sequences - provides powerful evidence of evolutionary relationships. The more similar the DNA sequences between two species, the more recently they shared a common ancestor.
Cladistics is a scientific method for constructing phylogenetic trees based on shared derived characteristics. This approach focuses on features that are unique to certain groups and their descendants. Scientists use cladistics to create cladograms, special diagrams that show evolutionary relationships.
Cool Connection: The DNA in your cells is more similar to chimpanzee DNA than chimpanzee DNA is to gorilla DNA - that's why humans and chimps are positioned closer on phylogenetic trees!
Reading Phylogenetic Trees
Clades are groups that include an ancestor and all its descendants - like branches on a family tree. For example, all mammals form a clade because they share a common ancestor. A valid clade must include the common ancestor and all its descendants.
Nodes on phylogenetic trees represent the common ancestors where branching occurs. Each branch point shows where lineages split and began to evolve separately. The branch lengths might represent time or the amount of genetic change between groups.
Phylogenetic trees help scientists identify convergent evolution, where unrelated species develop similar traits due to similar environmental pressures. They also show divergent evolution, where closely related species develop different traits as they adapt to different environments.
Study Hack: When studying for a test on phylogeny, practice drawing simple phylogenetic trees of familiar animal groups (like mammals, birds, and reptiles) to reinforce your understanding of evolutionary relationships.
Applications and Importance of Phylogeny
Phylogenetic analysis has practical applications across many scientific fields. Medical researchers use it to track disease evolution, conservationists apply it to protect endangered species, and agricultural scientists use it to develop better crops.
Understanding phylogeny helps predict unknown traits in organisms. If a plant species is closely related to others with medicinal properties, scientists might investigate it for similar useful compounds. This application has led to important discoveries in medicine and biotechnology.
Phylogeny also gives us the big picture of life's history on Earth. It helps us understand major evolutionary transitions, like how land vertebrates evolved from fish or how flowering plants diversified. These insights connect all biology topics, from genetics to ecology.
Big Idea: Phylogeny isn't just about the past - it helps scientists make predictions about how species might respond to future challenges like climate change or disease outbreaks.
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Stefan S
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This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
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Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
I think it’s very much worth it and you’ll end up using it a lot once you get the hang of it and even after looking at others notes you can still ask your Artificial intelligence buddy the question and ask to simplify it if you still don’t get it!!! In the end I think it’s worth it 😊👍 ⚠️Also DID I MENTION ITS FREEE YOU DON’T HAVE TO PAY FOR ANYTHING AND STILL GET YOUR GRADES IN PERFECTLY❗️❗️⚠️
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Knowunity is the BEST app I’ve used in a minute. This is not an ai review or anything this is genuinely coming from a 7th grade student (I know 2011 im young) but dude this app is a 10/10 i have maintained a 3.8 gpa and have plenty of time for gaming. I love it and my mom is just happy I got good grades
Brad T
Android user
Not only did it help me find the answer but it also showed me alternative ways to solve it. I was horrible in math and science but now I have an a in both subjects. Thanks for the help🤍🤍
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
I found this app a couple years ago and it has only gotten better since then. I really love it because it can help with written questions and photo questions. Also, it can find study guides that other people have made as well as flashcard sets and practice tests. The free version is also amazing for students who might not be able to afford it. Would 100% recommend
Aubrey
iOS user
Best app if you're in Highschool or Junior high. I have been using this app for 2 school years and it's the best, it's good if you don't have anyone to help you with school work.😋🩷🎀
Marco B
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This app is phenomenal down to the correct info and the various topics you can study! I greatly recommend it for people who struggle with procrastination and those who need homework help. It has been perfectly accurate for world 1 history as far as I’ve seen! Geometry too!
Paul T
iOS user
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
I think it’s very much worth it and you’ll end up using it a lot once you get the hang of it and even after looking at others notes you can still ask your Artificial intelligence buddy the question and ask to simplify it if you still don’t get it!!! In the end I think it’s worth it 😊👍 ⚠️Also DID I MENTION ITS FREEE YOU DON’T HAVE TO PAY FOR ANYTHING AND STILL GET YOUR GRADES IN PERFECTLY❗️❗️⚠️
Thomas R
iOS user
Knowunity is the BEST app I’ve used in a minute. This is not an ai review or anything this is genuinely coming from a 7th grade student (I know 2011 im young) but dude this app is a 10/10 i have maintained a 3.8 gpa and have plenty of time for gaming. I love it and my mom is just happy I got good grades
Brad T
Android user
Not only did it help me find the answer but it also showed me alternative ways to solve it. I was horrible in math and science but now I have an a in both subjects. Thanks for the help🤍🤍
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
I found this app a couple years ago and it has only gotten better since then. I really love it because it can help with written questions and photo questions. Also, it can find study guides that other people have made as well as flashcard sets and practice tests. The free version is also amazing for students who might not be able to afford it. Would 100% recommend
Aubrey
iOS user
Best app if you're in Highschool or Junior high. I have been using this app for 2 school years and it's the best, it's good if you don't have anyone to help you with school work.😋🩷🎀
Marco B
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This app is phenomenal down to the correct info and the various topics you can study! I greatly recommend it for people who struggle with procrastination and those who need homework help. It has been perfectly accurate for world 1 history as far as I’ve seen! Geometry too!
Paul T
iOS user
Understanding AP Biology 7.8: Phylogeny
Phylogeny helps us understand how all living things are related through evolution. It's like creating a family tree for different species to see how they evolved from common ancestors over time. Understanding these relationships helps explain why organisms have certain... Show more
Understanding Phylogeny
Phylogeny is the study of evolutionary relationships between organisms. Scientists use phylogenetic trees to visualize these relationships, showing how species are connected through their evolutionary history. These tree-like diagrams help us see which species share recent common ancestors.
When you look at a phylogenetic tree, each branch point represents an ancestor from which different species evolved. The diagram helps scientists organize life based on evolutionary history rather than just physical appearance.
The concept of phylogeny is based on the fundamental idea that all living organisms on Earth share a common ancestor if you go back far enough in time.
Quick Tip: When examining a phylogenetic tree, focus on the branching patterns rather than the physical distance between species on the diagram – the pattern shows relatedness, not physical similarity.
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Common Ancestry and Classification
All living organisms share a common ancestor - a powerful idea that forms the foundation of evolutionary theory. Species change over time through a process called descent with modification, which explains how different species evolve from shared ancestors.
Scientists use a hierarchical classification system to organize living things based on their evolutionary relationships. This system moves from broad to specific categories: domain, kingdom, phylum, class, order, family, genus, and species. The more categories two organisms share, the more closely related they are.
Homologous structures provide important evidence for evolutionary relationships. These are body parts that have similar underlying structure and development but might serve different functions. For example, a human arm, bat wing, and whale flipper all have the same basic bone arrangement despite their different uses.
Remember This: Taxonomy (how we classify organisms) is constantly being revised as we learn more about evolutionary relationships through new scientific discoveries.
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Evidence for Evolutionary Relationships
Analogous structures look similar and perform similar functions but evolved independently. Unlike homologous structures, they don't indicate shared ancestry. Think of bird wings and butterfly wings - both for flying but with completely different origins and structures.
Comparing molecular homology - similarities in DNA, RNA, and protein sequences - provides powerful evidence of evolutionary relationships. The more similar the DNA sequences between two species, the more recently they shared a common ancestor.
Cladistics is a scientific method for constructing phylogenetic trees based on shared derived characteristics. This approach focuses on features that are unique to certain groups and their descendants. Scientists use cladistics to create cladograms, special diagrams that show evolutionary relationships.
Cool Connection: The DNA in your cells is more similar to chimpanzee DNA than chimpanzee DNA is to gorilla DNA - that's why humans and chimps are positioned closer on phylogenetic trees!
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Reading Phylogenetic Trees
Clades are groups that include an ancestor and all its descendants - like branches on a family tree. For example, all mammals form a clade because they share a common ancestor. A valid clade must include the common ancestor and all its descendants.
Nodes on phylogenetic trees represent the common ancestors where branching occurs. Each branch point shows where lineages split and began to evolve separately. The branch lengths might represent time or the amount of genetic change between groups.
Phylogenetic trees help scientists identify convergent evolution, where unrelated species develop similar traits due to similar environmental pressures. They also show divergent evolution, where closely related species develop different traits as they adapt to different environments.
Study Hack: When studying for a test on phylogeny, practice drawing simple phylogenetic trees of familiar animal groups (like mammals, birds, and reptiles) to reinforce your understanding of evolutionary relationships.
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Applications and Importance of Phylogeny
Phylogenetic analysis has practical applications across many scientific fields. Medical researchers use it to track disease evolution, conservationists apply it to protect endangered species, and agricultural scientists use it to develop better crops.
Understanding phylogeny helps predict unknown traits in organisms. If a plant species is closely related to others with medicinal properties, scientists might investigate it for similar useful compounds. This application has led to important discoveries in medicine and biotechnology.
Phylogeny also gives us the big picture of life's history on Earth. It helps us understand major evolutionary transitions, like how land vertebrates evolved from fish or how flowering plants diversified. These insights connect all biology topics, from genetics to ecology.
Big Idea: Phylogeny isn't just about the past - it helps scientists make predictions about how species might respond to future challenges like climate change or disease outbreaks.
We thought you’d never ask...
What is the Knowunity AI companion?
Our AI companion is specifically built for the needs of students. Based on the millions of content pieces we have on the platform we can provide truly meaningful and relevant answers to students. But its not only about answers, the companion is even more about guiding students through their daily learning challenges, with personalised study plans, quizzes or content pieces in the chat and 100% personalisation based on the students skills and developments.
Where can I download the Knowunity app?
You can download the app in the Google Play Store and in the Apple App Store.
Is Knowunity really free of charge?
That's right! Enjoy free access to study content, connect with fellow students, and get instant help – all at your fingertips.
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The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
I think it’s very much worth it and you’ll end up using it a lot once you get the hang of it and even after looking at others notes you can still ask your Artificial intelligence buddy the question and ask to simplify it if you still don’t get it!!! In the end I think it’s worth it 😊👍 ⚠️Also DID I MENTION ITS FREEE YOU DON’T HAVE TO PAY FOR ANYTHING AND STILL GET YOUR GRADES IN PERFECTLY❗️❗️⚠️
Thomas R
iOS user
Knowunity is the BEST app I’ve used in a minute. This is not an ai review or anything this is genuinely coming from a 7th grade student (I know 2011 im young) but dude this app is a 10/10 i have maintained a 3.8 gpa and have plenty of time for gaming. I love it and my mom is just happy I got good grades
Brad T
Android user
Not only did it help me find the answer but it also showed me alternative ways to solve it. I was horrible in math and science but now I have an a in both subjects. Thanks for the help🤍🤍
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
I found this app a couple years ago and it has only gotten better since then. I really love it because it can help with written questions and photo questions. Also, it can find study guides that other people have made as well as flashcard sets and practice tests. The free version is also amazing for students who might not be able to afford it. Would 100% recommend
Aubrey
iOS user
Best app if you're in Highschool or Junior high. I have been using this app for 2 school years and it's the best, it's good if you don't have anyone to help you with school work.😋🩷🎀
Marco B
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This app is phenomenal down to the correct info and the various topics you can study! I greatly recommend it for people who struggle with procrastination and those who need homework help. It has been perfectly accurate for world 1 history as far as I’ve seen! Geometry too!
Paul T
iOS user
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
I think it’s very much worth it and you’ll end up using it a lot once you get the hang of it and even after looking at others notes you can still ask your Artificial intelligence buddy the question and ask to simplify it if you still don’t get it!!! In the end I think it’s worth it 😊👍 ⚠️Also DID I MENTION ITS FREEE YOU DON’T HAVE TO PAY FOR ANYTHING AND STILL GET YOUR GRADES IN PERFECTLY❗️❗️⚠️
Thomas R
iOS user
Knowunity is the BEST app I’ve used in a minute. This is not an ai review or anything this is genuinely coming from a 7th grade student (I know 2011 im young) but dude this app is a 10/10 i have maintained a 3.8 gpa and have plenty of time for gaming. I love it and my mom is just happy I got good grades
Brad T
Android user
Not only did it help me find the answer but it also showed me alternative ways to solve it. I was horrible in math and science but now I have an a in both subjects. Thanks for the help🤍🤍
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
I found this app a couple years ago and it has only gotten better since then. I really love it because it can help with written questions and photo questions. Also, it can find study guides that other people have made as well as flashcard sets and practice tests. The free version is also amazing for students who might not be able to afford it. Would 100% recommend
Aubrey
iOS user
Best app if you're in Highschool or Junior high. I have been using this app for 2 school years and it's the best, it's good if you don't have anyone to help you with school work.😋🩷🎀
Marco B
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This app is phenomenal down to the correct info and the various topics you can study! I greatly recommend it for people who struggle with procrastination and those who need homework help. It has been perfectly accurate for world 1 history as far as I’ve seen! Geometry too!
Paul T
iOS user