I believe this answers your question (From http://www.scholastic.com/browse/article.jsp?id=3753866)
Around 600 B.C., Greece developed one of the great civilizations in the history of the world. Sculpture became one of the most important forms of expression for the Greeks.
The Greek belief that "man is the measure of all things" is nowhere more clearly shown than in Greek sculpture. The human figure was the principal subject of all Greek art. Beginning in the late 7th century B.C., sculptors in Greece constantly sought better ways to represent the human figure.
The Greeks developed a standing figure of a nude male, called the Kouros or Apollo. The Kouros served to depict gods and heroes. The Kore, or standing figure of a draped female, was more graceful and was used to portray maidens and goddesses. The winged female figure, or Nike, became the personification of victory.
The fact that Greek sculptors concentrated their energies on a limited number of problems may have helped bring about the rapid changes that occurred in Greek sculpture between the 7th century and the late 4th century B.C. The change from abstraction to naturalism, from simple figures to realistic ones, took place during this period. Later figures have normal proportions and stand or sit easily in perfectly balanced poses.
Historians have adopted a special set of terms to suggest the main changes in the development of Greek sculpture and of Greek art in general. The early, or Archaic, phase lasted about 150 years, from 625 to 480 B.C. A short interval called Early Classical or Severe, from 480 to 450 B.C., was followed by a half century of Classical sculpture. Late Classical indicates Greek art produced between 400 and 323 B.C., and Hellenistic art was made from 323 to 146 B.C.
The most important function of Greek sculpture was to honor gods and goddesses. Statues were placed in temples or were carved as part of a temple. Greek temples were shrines created to preserve the images of the gods. The people worshiped outdoors.
Greek sculpture changed with Greek civilization. Praxiteles' Hermes is slimmer and more elegant than the strong, vigorous SpearBearer, by Polykleitos. Figures by Skopas from the Mausoleum at Halicarnassus are harsher and more dramatic than the quiet, controlled figures by Phidias.
Hellenistic sculptors emphasized the human figure. They reflected the great changes in their world when they treated in new ways subjects traditionally favored by earlier Greek sculptors. A new interest developed in the phases of life, from childhood to extreme old age. Sculptors described their figures in as natural and exact a way as possible. An ill old woman hobbles painfully back from the market; a little boy almost squeezes a poor goose to death.
The Greeks were defeated by the Romans, but the Hellenistic style lasted for centuries. Greek sculpture survived because the Romans were greatly impressed by Greek art. From the early days of the republic, Romans imported examples of Greek art, ordered copies of famous Greek works, and commissioned Greek sculptors to do Roman subjects.