Organisms can be classified in the same species by morphology and

Reproductive isolation

Explanation:

The members of the same species share some morphological features. They are able to interbreed and produce fertile progeny. if two or more organisms share common morphological traits and are able to interbreed, they belong to the same species.

The organisms from different species can not interbreed; if they interbreed, the produced progeny is sterile.

The Victorian era was during Queen Victoria's reign. During her long  reign there was peace and prosperity. It began in 1837 (beginning of Victoria's reign) and ended in 1901 (her death). Hopefully this helps.