How Blood Evolved (Many Times)

↓ More info below ↓

Blood is one of the most revolutionary features in our evolutionary history. Over hundreds of millions of years, the way in which blood does its job has changed over and over again. As a result, we animals have our familiar red blood. But also blue blood. And purple, and green, and even white.

Produced for PBS Digital Studios.

Super special thanks to the following Patreon patrons for helping make Eons possible:

Katie Fichtner, Anthony Callaghan, Renzo Caimi Ordenes, John Vanek, Neil H. Gray, Marilyn Wolmart, Esmeralda Rupp-Spangle, Gregory Donovan, Ehit Dinesh Agarwal, الخليفي سلطان , Gabriel Cortez, Marcus Lejon, Robert Arévalo, Robert Hill, Kelby Reid, Todd Dittman, Betsy Radley, PS, Colin Sylvester, Philip Slingerland, Jose Garcia, Eric Vonk, Tony Wamsley, Henrik Peteri, Jonathan Wright, Jon Monteiro, James Bording, Brad Nicholls, Miles Chaston, Michael McClellan, Jeff Graham, Maria Humphrey, Nathan Paskett, Connor Jensen, Daisuke Goto, Hubert Rady, Yuntao Zhou, Gregory Kintz, Tyson Cleary, Chandler Bass, Maly Lor, Joao Ascensao, Tsee Lee, Sarah Fritts, Ruben Winter, Ron Harvey Jr, Jacob Gerke, Alex Yan

Want to follow Eons elsewhere on the internet?

References:

[NaturesTemper]

I'd love to see how hair evolved. And the difference between mammal and arthropod hair.

[JoaoPedro-qpcw]

That guy asking for the blood video since forever must be very happy

[Twatical]

You've done nothing but inform the mosquito army of our greatest secret.

[raychumon]

i see lots of people saying 'finally' but not enough saying 'thank you', so... thank you for making the video so many of us asked for!!

[iNuuutz]

PBS Eons: *releases video about blood*

Mosquitoes: *Heavy breathing*

[deancyrus]

I understood about 5% of that. That's 5% more than i knew before. Really interesting stuff thanks.

[JonathanRootD]

What blows my mind is that for around 90% of Earth's existence we only had simple life. Larger complex life didn't arise until much more recently.

[enderflashria]

*the question I've seen in the comments of every single video and its finally here*

[johncnorris]

Dracula: I want to drink your iron based protein structures with hemogloben designed to transport oxygen.
Scientist: Yeah, okay.

[ericman]

You could say thats a bloody good subject

[SecNut]

How the hell did butterflies evolve to melt themselves and reform into a completely different shape?

[Shaden]

If life had to adapt to a snowball Earth at least twice, that would explain why copper was adopted early on to fix oxygen in their blood. As copper works better in cold temperatures. So it makes sense that life coming out of this snowball Earth used copper as they diversified into the Ediacaran period life forms.

[ferna]

Amazing. First time I hear about copper being used instead of iron.

Great job, perfectly explained.

[CargodHera]

Thank you, Hank Green for explaining even the most complex subjects in an entertaining and engaging way.

[nolanwestrich]

I've seen at least 3 comments asking for this episode, and I thought the idea was too. Thanks for the video!

[theshermanator]

“They all have bilateral symmetry”

Flatfish: “Am I a joke to you?”

[jj-qrro]

I gasped out loud multiple times when watching this! Science is so interesting thank you for providing another platform to make science more accessible

[mooxim]

As a dungeon master for d&d, I need to make a solid mental note about this. Lizards and lizardfolk can have green blood, arthropods can have blue blood, worms can have purple blood (awesome) and arctic beasts can bleed a clearish, white blood.
I might stick with describing arctic beasts having red blood because I'd like to avoid unnecessary semen jokes and the mental image of red blood on white snow is always very evocative.

[Gay_Priest]

Family: blood is thicker than water
Me: *angry ice fish noises*

[RickySTT]

2:54 Despite their adult appearance, sea stars are phylogenetically bilateral animals (Eumetazoa, Bilateria, Nephrozoa (≈Coelomata), Deuterstoma, Echinodermata, Asterozoa, Asteroidea). Their blood is degenerate compared to other bilaterians, but they do indeed have an internal body cavity and an active circulatory system, unlike sponges, jellies, and ctenophores.