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.
However, organ is a group of organized tissues performing specific or group of functions. â¢ Gland always secretes substances but not all the organs secrete substances. â¢ Gland is always a tubelike structure but organ is not always in that nature. Ex: liver is a dense organ but stomach is a hollow organ.