</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.
A species is often defined as the largest group of organisms where two hybrids are capable of reproducing fertile offspring, typically using sexual reproduction. While in many cases this definition is adequate, the difficulty of defining species is known as the species problem.ractically, biologists define species as populations of organisms that have a high level of genetic similarity. This may reflect an adaptation to the same niche, and the transfer of genetic material from one individual to others, through a variety of possible means.