The species theory, polygenism, held that human races were of different lineages and suggested a hierarchy outlined in the Chain of Being that positioned Africans between man and lower primates.
No, they are involved in the Circulatory System which is responsible for pumping and channelling blood to and from the body and lungs with heart, blood and blood vessels. no veins are not considered an organ because they are a grouping of different tissues like a organ.
Nutrients such as oxygen and the likes are transported all throughout the different part of the body through the blood vessels (composed of arteries, arterioles, capillaries, venules and veins). Many scientists believe that blood is a specialized form of connective tissue.The reason is because of its origin in the bones and the presence of fibers in the form of fibrinogen. Not all liquids can be a connective tissue.The only reason why blood is considered that way is due to the fact that is has a concentration of âground substances, like calcium, minerals and phosphorus in its extra-cellular matrix.he Fibrous connective tissue is found in ligaments and tendons in the body. It is composed of closely packed collagenous fibers. There is also the special connective tissue and blood is among these âspecialized tissues,.