Answers to the ad hominen attack, in unordered order.
PARASITES CAN SPLIT SPECIES IN TWO
Scientists at the University of Rochester in New York found that a bacterial parasite might have helped split one wasp species into two. The germ, known as Wolbachia, prevents the successful development of offspring between the two very closely related species. The germ damages the sperm of its male host, rendering it infertile when paired with an uninfected female. However, the researchers say that when the damaged sperm is introduced into an infected female, the Wolbachia actually "rescues" the sperm. Infected females automatically pass Wolbachia on to all their offspring. The researchers discovered that the two species can actually interbreed if given an antibiotic to kill Wolbachia, resulting in hybrids that are not sterile as other hybrids, such as mules, usually are. "This is the best evidence of a parasite contributing to speciation that we've seen," says researcher John Werren. The results of the study are published in the journal Nature.
Allopatric Speciation When a barrier, such as a stretch of sea or a mountain range, separates different populations of a particular species, the populations may no longer be capable of crossing the barrier to interbreed. Speciation caused by geographic isolating mechanisms, or allopatric speciation, is evident in the many different populations of pupfish that live in the Death Valley region of California and Nevada. About 50,000 years ago this region had a damp, rainy climate and was peppered by lakes and ponds connected by streams and rivers. Over time, rainfall decreased significantly, and by about 4,000 years ago, this region was a desert. The interconnected lakes and streams dried up, and in their place remained a series of small, isolated stream-fed ponds. Each pond is home to a different species of pupfish, specially adapted to its pond's unique temperature and mineral composition. Biologists speculate that all of these species of pupfish descended from a single species that inhabited the interconnected lakes and streams of the region about 50,000 years ago. As the lakes and streams dried up, the dry ground that separated them became a geographical isolating mechanism that prevented the individual populations from interbreeding. Consequently, the many pupfish populations evolved independently.
BSympatric Speciation In sympatric speciation, isolating mechanisms may be triggered by differences in habitat, sexual reproduction, or heredity. Similar plants may fail to breed together because their flowering seasons are different. Many different types of rain forest orchids, for example, cannot interbreed because they flower on different days. Some animals mate only if they recognize characteristic color patterns or scents of their own group. Other organisms, particularly birds, are stimulated to breed only after witnessing a song, display, or other courtship ritual that is characteristic in their group (see Animal Courtship and Mating).
Sometimes two subpopulations of the same species do not produce offspring with one another, even though they come into breeding contact. This may be due, for example, to reproductive incongruities between two subpopulations that cause embryos to die before development and birth. In other instances, if viable offspring are produced, reproductive isolation is still maintained because the offspring are sterile. For example, asses and horses are capable of mating, but their offspring are usually sterile. Both types of reproductive dysfunction occur when the hereditary factors of the two groups have become incompatible in some way and cannot combine to produce normal offspring.
CGradual Change Speciation may occur even when no isolating mechanism is present. In this case, a new species may form through the slow modification of a single group of organisms into an entirely new group. The evolving population gradually changes over the course of generations until the organisms at the end of the line appear very different from the first. Foraminifera, a tiny species of marine animals that live in the Indian Ocean, demonstrate this process, known as vertical or phyletic evolution. From about 10 million to 6 million years ago, the species remained relatively unchanged. These organisms then began a slow and gradual change, lasting about 600,000 years, that left them so unlike their ancestors that biologists consider them an entirely new species.
There is another category to speciation, I forget what it is.
And gradualism is debunked. It is shown (I lost the link) that if evolution occurred as suggested, it went through peaks and troughs. And I really forgot what entropy had to do with it, but entropy is probably my favorite subject of subjects. It has to do a lot with the eye of a bird and artificial intelligence. But please, don't ask me to explain that!
edit: I forgot one: I think there is only one equilibrium
Punctuated Equilibria Evolutionary theory has undergone many further refinements in recent years. One such theory challenges the central idea that evolution proceeds by gradual change. In 1972 the American paleontologists Stephen Jay Gould and Niles Eldredge proposed the theory of punctuated equilibria. According to this theory, trends in the fossil record cannot be attributed to gradual transformation within a lineage, but rather result from quick bursts of rapid evolutionary change. In Darwinian theory, new species arise by gradual, but not necessarily uniform, accumulation of many small genetic changes over long periods of geologic time. In the fossil record, however, new species generally appear suddenly after long periods of stasis-that is, no change. Gould and Eldredge recognized that speciation more likely occurs in small, isolated, peripheral populations than in the main population of the species, and that the unchanging nature of large populations contributes to the stasis of most fossil species over millions of years. Occasionally, when conditions are right, the equilibrium state becomes "punctuated" by one or more speciation events. While these events probably require thousands or tens of thousands of years to establish effective reproductive isolation and distinctive characteristics, this is but an instant in geologic time compared with an average life span of more than ten million years for most fossil species. Proponents of this theory envision a trend in evolutionary development to be more like climbing a flight of stairs (punctuations followed by stasis) than rolling up an inclined plane (Darwinian gradualism). |
