Organisms that have this ability possess a specialized leading digit known as an alula. Animals that have lost this ability tend to have symmetrical remiges (“re-MEE-jez”). Echelon formations are adopted by groups of organisms with this ability. Structures that confer this ability are categorized as (10[1])primary or secondary, and can include small serrations to reduce noise. Tree-down and ground-up are two theories for the evolution (10[1])of this ability, (10[1]-5[1])seen in the transition species Archaeopteryx (“arch-ee-op-te-rix”). Organisms (10[1]-5[1])with this ability have hollow bones. (10[2])For 10 points, (10[2])name this ability to generate lift in the air possessed by animals like birds. (10[1])■END■ (10[1])