</a> Courtesy Smithsonian Institution National Numismatic Collection. Rare Currency at The Smithsonian The previous coin's older brother the 1849, Gold Rush era double eagle gold coin is valued by collectors the world over. It was the United States of America's first $20 denominational gold coin. Courtesy Smithsonian Institution National Numismatic Collection.
subspecies - (biology) a taxonomic group that is a division of a species; usually arises as a consequence of geographical isolation within a species. race. biological science, biology - the science that studies living organisms. taxon, taxonomic category, taxonomic group - animal or plant group having natural relations.
) is one of the basic units of biological classification and a taxonomic rank. A species is often defined as the largest group of organisms where two hybrids are capable of reproducing fertile offspring, typically using sexual reproduction.ristotle used the words genus and species to mean generic and specific categories. Aristotle and other pre-Darwinian scientists took the species to be distinct and unchanging, with an  essence , like the chemical elements.