Question

The classification system for organisms has changed from seven levels to eight. This happened because

Answer 1

Because scientist found another criteria for classifying organisms such as their DNA composition

Evidences that Taxonomy uses to group or categorizes species range from 
1.       "Fossil Records 
2.       Comparative anatomy 
3.       Comparative embryology 
4.       Biochemical information 
5.       Cellular structure 
6.       Behavior" 
We also suggest that taxonomy has played various roles mainly in many aspects in Zoology, Botany, Anatomy and Physiology –aspects that include animal and human structures and functions. As the biotic community is so diverse it is classified to Biodiversity and the existence of properly assorting by set standard. 

Answer 2

Answer:

The modern taxonomic classification system has eight levels as Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species.

The new level which has been added to the seven levels taxonomic system proposed by the Carolus Linnaeus is "Domain" which is the most inclusive group of system.

The domain system is divided into 3 forms:  archaea, bacteria, and eukaryotes which was introduced by Carl Woese in 1977 were added to the older system which did not show the phylogenetic relationships between organism as prokaryotes were evolved into two groups eubacteria and archaebacteria while eukaryotes are kept a separate group.