Ashtallan

The Ashtallan were a race of people that lived on the planet Ashtallah.

Biology
They were capable of self-healing and regrowing limbs, and had such long, untroubled lives that they had no need for reproduction. They had transparent grey-blue skin.

When introduced into their system however, human blood had lethal effects on an Ashtallan, causing their body to liquify and break apart, turning a pinkish-red hue. The First Doctor suspected this was due to the red blood cell attacking the Ashtallan system. (AUDIO: The Invention of Death)

Culture
The Ashtallans had no concepts for death or gender. Brenna and Sharlan were among the first scientists of their race, studying light. (AUDIO: The Invention of Death)

History
The Ashtallans were fascinated by the First Doctor, Ian, Barbara and Susan's opaque pink flesh, as well as their alien concepts. They did not understand that the new arrivals could get seriously hurt from injuries. Brenna covertly used a sample of Barbara's blood on other Ashtallans because they saw promise in shorter lifespans, if this had led to such marvels as the Doctor's TARDIS. Though they did not fully understand what this meant, Brenna introduced death for Ashtallans.

With the Doctor's help, Brenna and Sharlan also succeeded in producing an Ashtallan child from their own cells. Though they had no such concept before the TARDIS' arrival, Sharlan and Brenna experienced love for each other. After Sharlan died protecting the child from the plague they started, Brenna reared their child. (AUDIO: The Invention of Death)