from The American Heritage® Dictionary of the English Language, 4th Edition
- n. Biology The theory that the evolution of a species is influenced most strongly by internal factors and is not subject to the external forces of natural selection.
- n. The theory that all cultures pass through sequential periods in the same order.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. A series of similar mutations in successive generations, producing evolutionary change.
from The Century Dictionary and Cyclopedia
- n. The direct or immediate origin of species, according to the opinion that it takes place by the ‘organic growth’ of one species into another in a definite line which is predetermined by the constitution which outward circumstances have given to each organism.
ortho- + -genesis (Wiktionary)