What does it mean when psychologists say that there are biological constraints on classical conditioning?

Looking at the animals (and humans for that matter) the psychologists say that there are biological constraints as both humans and animals can learn the effects of a certain event or a situation. So biologically animals and humans are predisposed to learn how to behave (and also learn skills) in order to survive, that is why they will for instance avoid and have aversion to food that causes them to vomit.   

in 342 bc j._c. egypt fell into the hands of the persians, under the reign of nectanebo ii

greek city-states unite in a revolt against the persian empire at the beginning of the fifth century bc. j.-c  

from the year 660 or 659 bc ad, cyrus preached the revolt against the medes to deliver the persians.

well considering i can't see the graph, it's probably prices