Flight is a remarkable adaptation that is most commonly associated with birds. Yet not all birds fly and there are other groups of animals that share airspace with the birds. In fact, birds cannot even claim to be the first animals to grasp the skills of flight. The insects beat them into the skies by about 200 million years (Attenborough 1998, 12).
Because flight evolved separately in three different groups of animals, it is an example of convergent evolution. If you would like to explore how flight evolved in various groups of animals, please see:
- Pterosaurian Flight (UC Berkely, Museum of Paleontology)
- Avian Flight (UC Berkely, Museum of Paleontology)
- Chiropteran Flight (UC Berkely, Museum of Paleontology)
- Insect Flight (Hooper Virtual Paleontological Museum)
All animals that fly have wings. To understand the evolution of flight, it helps to consider how wings may have evolved:
- wings may have evolved from forelimbs used in the capture of small prey
- wings may have evolved to assist animals as they jumped up from the ground
- wings may have evolved as part of sexual display features
- wings may have evolved to help animals glide efficiently (UCB 2006)
These observations provide possible explanations as to how flight may have evoled, but they do not address why flight evolved. So let's take a look at some hypotheses that explain why flight might have evolved:
- to evade predators
- to capture prey
- to provide a more efficient means of locomotion
- to enable better use of hindlimbs for defense
- to colonize an unoccupied niche (UCB 2006)
Now let's turn our attention to flight in birds. In birds, flight evolution required feathers. Scientists also believe that flight required birds to be endothermic so they could sustain the energy level needed for flapping wings. But the rest of the story, the nuts and bolds of how flight evolved, remains shrouded in debate. There are two basic hypotheses:
- 'Trees-down' Theory - Proposes that flight developed from gliding, that is, birds first took to the air by jumping from the branches of trees and gliding for a distance. Over time, refinements to wings and feathers enabled birds to fly more efficiently.
- 'Ground-Up' Theory - Suggests that early birds lived on the ground and took to hopping up from the ground to catch prey.
Sources
- Attenborough, David. 1998. The Life of Birds. London: BBC Books.
- Sibley, David Allen. 2001. The Sibley Guide to Bird Life & Behavior. New York: Alfred A. Knopf.
- The University of California, Berkely (UCB). 2006 (Accessed Online). Museum of Paleontology.
