How do you read Evolutionary Trees?

Did a doctor spitefully infect his ex-girlfriend with HIV? This video describes the first time an Evolutionary Tree* was used in a criminal court in America. Learn how to interpret the relatedness of organisms on any Evolutionary Tree... and find out whether the doctor actually did it.
*Also sometimes called a Phylogenetic Tree.

0:00 Introduction
0:29 Example of using evolutionary tree in court case
1:14 Trees depict organismal relationships
2:29 How to read evolutionary trees
3:17 Count the steps?
4:00 See which organisms are closest to each other?
5:20 Compare the Most Recent Common Ancestors?
6:37 Example of using evolutionary tree in court case conclusions

The paper behind this video:

Scientific Consulting by Cynthia Darnell
Cartoon Illustrations by Michelle Lotker

Images:
Elephant by Muhammad Mahdi Karim GFDL 1.2
Lion by Rufus46 CC BY-SA 3.0
Eagle by Vtornet CC BY-SA 3.0
Squid by Hans Hillewaert CC BY-SA 4.0
HIV micrograph by CDC/Dr. Edwin P. Ewing, Jr. / Public domain
T rex by Zissoudisctrucker CC BY-SA 4.0
Tiger by Lotse CC BY-SA 3.0
Polar Bear by Alan Wilson CC BY-SA 3.0
Grizzly Bear by Dwayne Reilander CC BY-SA 4.0
Flamingo by Charles J Sharp CC BY-SA 3.0
Snail by CJ Samson / Public domain
SARS-CoV-2 by NIAID-RML CC BY-SA 2.0

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[hebahamood]

I absolutely love your teaching style and personality! Thanks for including the criminal case as well

[swedishrobloxgamer]

This gave me so much motivation, it's weird hahah. You made this a lot easier and concrete and FUN. I've been studying biology now and i always find it hard because there are so many "ways" of wanting to read a tree like that. Our logic would say the closest, but it all about the most recent ancestor! Thank you, and very nice done!! I'm sure you've helped a lot of students by this simplyfied method and positvity

[anthonyhuang]

Wow, really well explained and such an interesting criminal case, thanks a lot for the video!

[emilyzhang]

This really helped me! Thank you so much for including the example of the HIV patient, that made it really interesting

[hathawayphd]

This is SO good! I love the mobile explanation - such an amazing visual aid!

[miguelolano]

Great video! Very informative. Keep up the great work!

[catherinepuellomora]

Amazing video, I learned and enjoyed at the same time. ❤️

[aneekaak]

I love the history lesson! Will definitely remember this topic now

[shawnhowe]

Well Done! This was so helpful for my epidemiology course

[esabellageorge]

thank you for this video! It was very helpful!

[nicorico]

I have a bio test in 2 days and evolutionary trees were the only thing I couldn’t grasp, but now I understand it thanks to your good teaching. Thank you!

[VeryBizzyIzzyy]

wow! as a gcse student this was so helpful and you clearly and concisely explained it, thank you so much :)

[lauryndejaperry]

thank you for the video! You explained it perfectly!

[James-qouz]

So how many “nodes” or intermediate species do we actually know of?

[MichiMind]

3:11 DONT COUNT THE STEPS

K makes all lines under it

[ScyllasSimp]

Thank you, I actually need this for my job. Didn't pay enough attention in my biodiversity course unfortunately.

[TH-uixh]

Thank you so much for this video, it helped me out a lot!

[gift-evbakoeosaghae]

Thank you so much! I finally understand the concept!

[Ashley-kvku]

Thanks I’ve really been wanting to learn about evolutionary trees and I loved this video it taught me a lot thank you so much for this video

[sofeaarina]

very interesting and engaging! love it