Why do we actually have blood?
July 28, 2017 by David Irving, The Conversation
Just as a village can't grow into a city without some form of transport (road, rail or river) that provides necessary interconnections for it to flourish, living things are limited in the size they can reach unless they have some form of circulatory system to transport nutrients and remove waste.
Single celled organisms such as bacteria and fungi, and some multicellular creatures such as sponges, corals and flatworms, simply absorb the nutrients they need and get rid of their waste using a passive process known as diffusion (which is much like soaking in and draining out).
https://medicalxpress.com/news/2017-07-blood.html
