Biochemist Linus Pauling stated that
Biological specificity is the set of characteristics of living organisms or constituents of living organisms of being special or doing something special. Each animal or plant species is special. It differs in some way from all other species. ...
...biological specificity is the major problem about understanding life.
Characteristics may further be described as being interspecific, intraspecific, and conspecific.
Interspecificity (literally between/among species), or being interspecific, describes issues between individuals of separate species. These may include:
Two or more individual organisms, populations, or taxa are conspecific if they belong to the same species. Where different species can interbreed and their gametes compete, the conspecific gametes take precedence over heterospecific gametes. This is known as conspecific sperm precedence, or conspecific pollen precedence in plants.