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How Blood Evolved (Many Times)

Season 2 Episode 9 | 9m 56s

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.

Aired: 01/17/19
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During the Permian Period many tetrapods, or four-limbed vertebrates, took to life in the trees.
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An apocalypse ended the Permian Period 252 million years ago, wiping out more than 80% of species.
The first saber-teeth and tusks evolve in the Late Permian and our ancestors, the cynodonts, appear.
For millions of years after the Great Dying microbes ruled the Earth.
An extinction in the Middle Permian decimates life, from a fossil reef to our ancient relatives.
The first herbivorous vertebrates evolve on the side of the amniote family tree leading to mammals.
Seed plants and amniotes adapt to dry climates, helping them thrive on Pangea in the Permian Period.
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Poll gauges voter enthusiasm for both parties a week before election
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Projections show no clear winner in Israel's election
School principal documents Indonesia's worst wildfires in a decade
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Artemizia Foundation, A New Path Forward, Recycling is no mystery in Bisbee, Thuy’s Noodle Shop.
Appraisal: Victorian Slide Chain & Diamond Bracelet
Aaron Glantz and Sophie Hills discuss AI companies' efforts to influence the midterms.
October 27, 2026 - PBS News Hour full episode
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Take a journey through the history of life on Earth.
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Camels' origins story begins in an environment you’d never expect: a rainforest.
The story of sloths is one of astounding ecological variability.
When Sharks Swam the Great Plains
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What happened to the largest shark in history?
Not too long ago, our early human ancestors were under threat of attack from predators.