The Origins of Soaring
The first creatures to soar upon slope and thermal lift were large winged creatures a couple hundred million years ago. With wingspans well over 20 feet and weighing well in excess of a 100 pounds, huge muscles would have been required to maintain flapping flight even with the denser air of that time providing more lift, so it is thought these creatures flew exclusively in lift by jumping off mountain tops.
In more recent times large soaring birds such as eagles and hawks, rely on finding lift for much of their flight.