Economic, technological, and strategic changes, however, have combined to blur this distinction.
Pollution, overfishing and changes in water temperature have combined to destroy a significant portion of them -- 10percentt or more by some estimates.
Several trends have combined to change that.
And now Mexico City — where movies, television, birth control, foreign tourism, the Internet, and sex education at public schools have combined to change the culture at breathtaking speed — appears to have decided that the policy no longer serves.
There are at least three major factors that have combined to change this.
A combination of factors including sophisticated ultrasound methods, fetal surgery, genetic science, premature birth survivability rates at younger ages have combined to change the landscape from a time when pro-choice advocates pitched abortion as no more morally significant than the removal of an appendix.
But over the last generation, they have combined with political changes to invert the electoral map.
Report contributor, Kitty Stewart from the London School of Economics, suggests the coalition's changes in the rules for claiming child tax credit, reductions in the childcare element of working tax credit, caps on overall benefits and changes to the local housing allowance have combined to hit low-income families hardest.
It appears likely that both the shorter-term processes of occasional extinction of all pools on single outcrops and subsequent recolonization, and the longer-term processes such as geological uplift and repeated cycles of sea level change with past episodes of glaciation have combined to shape patterns of genetic divergence in this species.
Social changes and a string of sordid scandals featuring priests have combined to put distance between two words often uttered as one: Catholic Ireland.
