Sunday, November 05, 2006
Ultimate causation
The two causes that contribute to ultimate causation are phylogenetic contingencies that contribute to the development of behavior and the second is adaptive significance. Phylogenetic constraints are generally factors that might stop certain lineages developing certain behavioral or morphological traits. Hence, it is no coincidence that generally birds are able to fly and mammals cannot. The evolutionary history of these lineages have made it profitable for birds to fly and for mammalian feet to remain planted on the ground. Adaptive significance is akin to asking what a trait is good for in an evolutionary context. Therefore, the adaptive significance of flight in birds might have enabled avian ancestors to escape from predators. However, it is not sufficient to apply these explanations where they seem convenient. These have been labeled Just So Stories by some biologists after Rudyard Kipling's tales for children about how animals came to be the way they are. To be rigorous, one must suppose a hypothesis and then test it scientifically. Hence, for avian flight, one can suppose that when birds are not at risk of being eaten, they might lose the ability to fly. This has been observed in bird faunas on oceanic islands such as New Zealand. Historically these land masses had no mammalian predators and so had a higher proportion of flightless bird species compared with avifaunas exposed to mammalian predation.
The two causes that contribute to ultimate causation are phylogenetic contingencies that contribute to the development of behavior and the second is adaptive significance. Phylogenetic constraints are generally factors that might stop certain lineages developing certain behavioral or morphological traits. Hence, it is no coincidence that generally birds are able to fly and mammals cannot. The evolutionary history of these lineages have made it profitable for birds to fly and for mammalian feet to remain planted on the ground. Adaptive significance is akin to asking what a trait is good for in an evolutionary context. Therefore, the adaptive significance of flight in birds might have enabled avian ancestors to escape from predators. However, it is not sufficient to apply these explanations where they seem convenient. These have been labeled Just So Stories by some biologists after Rudyard Kipling's tales for children about how animals came to be the way they are. To be rigorous, one must suppose a hypothesis and then test it scientifically. Hence, for avian flight, one can suppose that when birds are not at risk of being eaten, they might lose the ability to fly. This has been observed in bird faunas on oceanic islands such as New Zealand. Historically these land masses had no mammalian predators and so had a higher proportion of flightless bird species compared with avifaunas exposed to mammalian predation.
