More evidence for Macroevolution - Ontology, the science of developmental biology.
Embryology and developmental biology present some of the best evidence for macroevolution. It is a basic fact and correct to state that ontogeny creates phylogeny. This means that when we have knowledge of an organisms development (ontogeny) we can confidently predict certain aspects of the historical pathway (phylogeny) that was involved in the organisms evolution. Thus embryology provides testable confirmations and predictions about macroevolution. For example;
From embryological studies it is known that two bones of a developing reptile eventually form the quadrate and the articular bones in the hinge of the adult reptilian jaw. However, in the marsupial mammalian embryo, the same two structures develop, not into parts of the jaw, but into the anvil and hammer of the mammalian ear. This developmental information, coupled with common descent, indicates that the mammalian middle ear bones were derived and modified from the reptilian jaw bones during evolution. Accordingly, there is a very complete series of fossil intermediates in which these structures are clearly modified from the reptilian jaw to the mammalian ear.
There are numerous other examples in which an organism's evolutionary history is represented temporarily in its development. Early in development, mammalian embryos temporarily have pharyngeal pouches, which are morphologically indistinguishable from aquatic vertebrate gill pouches. This evolutionary relic reflects the fact that mammalian ancestors were once aquatic gill-breathing vertebrates. The pharyngeal pouches of modern fish embryos eventually become perforated to form gills. Mammalian pharyngeal pouches of course do not develop into gills, but rather give rise to structures that evolved from gills, such as the eustachian tube, middle ear, tonsils, parathyroid, and thymus. The arches between the gills, called branchial arches, were present in jawless fish and some of these branchial arches later evolved into the bones of the jaw, and, eventually, into the bones of the inner ear.
Many species of snakes and legless lizards initially develop limb buds in their embryonic development, only to reabsorb them before hatching. Similarly, modern adult whales, dolphins, and porpoises have no hind legs. Even so, hind legs, complete with various developing leg bones, nerves, and blood vessels, temporarily appear in the cetacean fetus and subsequently degenerate before birth.
Humans are classified by taxonomists as apes; one of the defining derived characters of apes is the lack of an external tail. However, human embryos initially develop tails in development. At between four and five weeks of age, the normal human embryo has 10-12 developing tail vertebrae which extend beyond the anus and legs, accounting for more than 10% of the length of the embryo. The embryonic tail is composed of several complex tissues besides the developing vertebrae, including a secondary neural tube (spinal cord), a notochord, mesenchyme, and tail gut. By the eighth week of gestation, the sixth to twelfth vertebrae have disappeared via cell death, and the fifth and fourth tail vertebrae are still being reduced. Likewise, the associated tail tissues also undergo cell death and regress.
Reptiles and birds lay eggs, and the emerging young use either an "egg-tooth" to cut through a leathery keratinous eggshell (as found in lizards and snakes) or a specialized structure, called a caruncle, to crack their way out of a hard calcerous eggshell (as found in turtles and birds). Mammals evolved from a reptile-like ancestor, and placental mammals (like humans and dogs) have lost the egg-tooth and caruncle (and, yes, the eggshell). However, monotremes, such as the platypus and echidna, are primitive mammals that have both an egg-tooth and a caruncle, even though the monotreme eggshell is thin and leathery. Most strikingly, during marsupial development, an eggshell forms transiently and then is reabsorbed before live birth. Though they have no need to hack through a hard egg-shell, several marsupial newborns (such as baby Brushtail possums, koalas, and bandicoots) retain a vestigial caruncle as a clear indicator of their reptilian, oviparous ancestry.
Not only does ontology provide us with testable confirmations and predictions about macroevolution it is easily falsifiable. Based on our standard phylogenetic tree, we may expect to find gill pouches or egg shells at some point in mammalian embryonic development (and we do). However, we never expect to find nipples, hair, or a middle-ear incus bone at any point in fish, amphibian, or reptilian embryos (and we don't) and any such findings would be in direct contradiction to evolutionary theory.
This is also the answer to Dixie's "DogCat" argument that cross genus evolution has never been observed. This is because evolutionary theory makes no such prediction. Instead, evolutionary theory predicts that ontogeny (developmental biology) creates phylogony (the historical pathway of evolution) in a manner that has a nested hierarchical structure. This prediction, on evolutionary theory, is supported by both observed and experimental data and thus Dixie's "DogCat" argument is a strawman.
