In this blogspot we will consider the amazing bird wing and the human hand. Surely, argue the Creationists, the feathered bird’s wing and the human hand in all their engineering splendor, near infinite complexity, and marvelously coordinated function must have been the product of a divine Creator able to build and coordinate such wonders all at once to allow for such integration of structure and function. However, until 380 MYA, such limbs did not exist. Fossils and embryos provide the wealth of clues that establish the evolution of these complex and various structures. Starting about 400 MYA, lobe finned fish emerged bearing the first suggestion of a limb. Its lobe-fins superficially looked like the rest of the fishes, but anatomically the bones inside the fins were larger, stronger, and more heavily muscled than any other fish up to that time.
It took tens of millions of years of changing lineages of lobe-fins for true limbs to take shape. As described earlier, Eusthenopteron–a 385 million year old fish–had fins that contained large rod-shaped bones linked to a pair of smaller bones, the pattern of modern human arms and legs. Tiktaalik roseae, a 375 million years old lobe-fin added wrist and ankle bones. This fish could have used its fins both to swim and to crawl on land. It could not have walked or rotated its shoulder, however. 365 MYA, lobe-fins gave rise to vertebrates with true fins which had now become true tetrapods, four footed, even toed creatures adapted to water by their ancestral gill bones and finned tails but able to waddle on land. Later still, tetrapods developed the basic plan of the limb and adapted it to new functions of digging, paddling, walking on land, and even flying.
Again, the genes responsible for the building of complex limbs were discovered to be tools-in-hand in the ancestral animals, and natural selection produced the necessary bit-by-bit of change that resulted in the marvelously adapted structures seen in modern animals. As in the other changes described, the genes came from the basic ones that lay out the body plan. They mark off the body from head to tail, then they become active in making tiny buds that become arms and legs and wings. The genes of early fish were reused to make fins. Subtle shifts in the genetic patterns resulted in changes in shape that produced arms, legs, hands and feet, and wings, all coming from machinery already in place.
Flight feathers of birds are brilliantly complex and marvelously functional. It would seem to be a leap of faith to conclude that evolution produced such a marvel. The basic anatomy of feathers involves a central vane from which hundreds of filaments and barbs sprout. The barbs sprout smaller filaments, some with grooves and some with hooks that zip the barbs together like Velcro. These airy
filaments create a lightweight plane that can lift a bird skyward. Birds pull their feathers apart to clean them, and then the barbs zip back together by themselves. In addition feathers perform such varied functions as are found in the club-winged manakin, a sparrow-size Ecuadorian bird which can rattle its wing feathers so loudly that they sing. Owl feathers have a natural stealth quality that dampens sound. Fuzzy down feathers provide warmth, and not least, extravagantly curved and colored feathers attract mates. As remarkable as all of these feather variations are, they all come from a basic pattern that started with reptilian scales.
The evolutionary link between feathers and scales is apparent in developing bird embryos. Placodes–discs of cells–are scattered across the surface of the early embryo. Some of the placodes grow into scales such as cover chickens’ legs, and others become feathers. The stepped evolution of feathers involved old genes being modified frequently for new uses. In reptile embryos specific genes demarcate the front and back of each scale as it develops from its placode. In bird embryos, each feather begins as a tube growing from a placode utilizing the same front and back genes. 150 MYA, these same genes took on the new role in dinosaurs, causing some to sprout feathers and feather-like growths that recent fossil finds have revealed.
Branch-like barbs came next. The development of baby downy feathers offers clues as to how that happened. As a new feather tube grows, it divides into strips which peel away into barbs. Minor genetic changes would have been necessary to result in the tube’s splitting. The same front and back genes mark the points around the tube where it will eventually split. Later birds developed the ability to turn downy feathers into veined feathers, and still later the changes in barbs that make the hooks that zip the barbs together were developed. Finally, the special plumage for hunting, swimming, and courting came into being from the original basic reptile scale genes. continued…