Elijah Williams worked at The Ohio State University Museum of Biological Diversity (2016-2018)
E: “All of this was happening in the ocean and in organisms that could use simple diffusion for moving gas and nutrients. They could keep operating as normal as the closed circulatory system evolved. Some simple animals don’t actually need blood. There is a section in the paper that describes, in detail, exactly how the first circulatory systems are thought to have evolved. I’ll copy and paste the relevant section here”:
How did the blood vascular system and endothelium evolve?
‘The coelomic and blood vascular systems (as well as excretory systems) arose within the mesoderm of triploblastic animals. Indeed, the appearance of the mesoderm provided new building material for animal construction and allowed for the evolution of increasingly complex and large animals. At some early evolutionary stage, perhaps in the ancestral triploblastic bilaterian condition, a subpopulation of mesodermal cells differentiated into a mesothelium whose apical side faced the coelom and whose basal side faced clefts (i.e., blood vessels) between the mesothelial walls.’
It’s a lot of material that will propagate a great number of questions.
“Some simple animals don’t actually need blood.”
Not pertinent to my question.
“The coelomic [the coelom is the main body cavity] and blood vascular systems (as well as excretory systems) arose within the mesoderm of triploblastic animals.”
Arose? How? Magic?
“the appearance of the mesoderm [the middle layer of an embryo in early development, between the endoderm and ectoderm] provided new building material for animal construction”
Appeared? How? Magic?
“a subpopulation of mesodermal cells differentiated into a mesothelium [the surface layer of the embryonic mesoderm]”
What was the mechanism that caused it to differentiate?
Okay, now I can alter my question:
How does the Theory of Evolution explain blood vessels mentioned in the statement below?
“whose apical [apex] side faced the coelom and whose basal [base] side faced clefts (i.e., blood vessels) between the mesothelial [membrane] walls”
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