There are four principles at work in evolution—variation, inheritance, selection and time. The theory of evolution by natural selection, first formulated in Darwin's book "On the Origin of Species" in 1859, is the process by which organisms change over time as a result of changes in heritable physical or behavioral traits.
1. First Stage: Dilation and Effacement of the Cervix
a. early phase
b. active phase
c. transition phase
2. Second Stage: Pushing and Birth
3. Third Stage: Delivery of the Placenta
Without backbone or having no backbone is considered as INVERTEBRATES.
hope its help...
--kcirejay:♥)
I think the answer would be mid-noon.