Does microevolution logically include macroevolution?

There are various ways in which reproductive isolation can be brought about. One is geographic isolation - this leads to allopatric speciation. Over time, geographic isolation means species become more and more different, due partly to differences in selection and partly to random drift. This was touted by Mayr to be the primary and most important way species form, but that view is probably outdated now.Another way you get speciation is parapatric speciation. Here there exist contiguous, adjoining populations that experience different selective forces in their different regions, so that different genotypes are advantageous in each. At some point, both populations benefit by avoiding mating with individuals from the other, so behavioral mechanisms evolve to prevent it and favor those individuals that adopt them. Think different courtship rituals.Finally, there is sympatric speciation where the process occurs within a contiguous population. The 'host-plant fidelity' model in herbivorous insects is an example here. Some individuals start feeding on a new plant species and leave viable offspring. Once they orient to this new plant to find mates, they no longer cross-breed with the parental population and embark on their own evolutionary trajectory.The term 'macroevolution' is typically used by evolutionary biologists to refer to cladistics and phylogenetics - the construction of trees to explain relationships between species and genera within higher order taxa. Since these higher order taxa are not objectively defined like 'species', the term 'clade' is often used to refer to a particular group of genera/species that are monophyletic (can be shown to share a single common ancestor). The combination of modern molecular techniques with conventional morphologically-based taxonomy has recently produced some really powerful inferences in cladistics. This is because the two independent approaches frequently converge on a very similar 'tree', as for example here. If you compare the Figures 1 through 4 you will see that entirely different 'branching rules' nevertheless converge on a very similar tree, the composite hypothesized in Figure 5. This is a macroevolutionary analysis. The reproductive isolation (whether accomplished geographically, behaviorally or ecologically) would logically come first. However, this applies specifically to amphimicitic (sexually outcrossing) species. For species with asexual reproduction there is no need for any specific isolating mechanism - all clones diverge independently and there is no real 'gene pool' at all unless sexual forms produced (as they often are on a seasonal basis, for example in aphids).

Not necessarily. The more complicated the organism and the more specialized its ecological niche, the more 'constraints' will limit its evolutionary possibilities. Bascially, yes. The distinction between the two is merely one of convenience as we try and look back in time to decifer the divergence of higher taxa. All macroevolution begins with microevolutionary changes within populations, but not all microevolutionary changes necessarily lead to macroevolutionary consequences. Good enough?This message has been edited by EZscience, 06-15-2005 11:28 AMThis message has been edited by EZscience, 06-15-2005 11:30 AM

Sorry - it's a goal not always realized. Actually, the specific criterium is reproductive isolation itself. There is no requirement for passage of time or any overt morphological differences. For example, I know of several situations where new species of insects were recognized solely because a particular parasitoid attacked one, but not the other. Sure enough, a simple crossing experiment showed them to be reproductively isolated moth species, although any taxonmist going by morphology alone could never tell them apart. So reproductive isolation is all that really matters and 'species' is the only taxonomic designation that has a true biological meaning. All the others do not. Because a lot of variation may be retained *within* species that doesn't necessarily have anything to do with whether or not speciation occurs. Species can also change genetically over time without splitting into two. This is why the phylogenetic species concept is separate from the biological species concept.Think of it this way. You and I are surely different in various 'microevolutionary' ways. That means that your kids and my kids and their decendents may differ in certain recognizable ways, but it doesn't imply that we will each give rise to a different surviving lineage of humans.Here is another example. We used a lot of DDT from the 1940's to the 1960's and many insects developed resistance to it independently. But the evolution of resistance is rarely without some cost. With DDT off the market, the alleles confering resistance in many species have receded to very low frequencies in insect populations because their alternatives are selectively favored with the pesticide isn't around. So pesticide resistance is a good example of a microevolutionary change that not only would be expected to have little consequence to macroevolutionary change in insects, it is actually reversible within species and can be lost.

Reproductive isolation is defined by genetic incompatibility.
In other words, you make reciprocal crosses of males and females from the two bear populations. If viable offspring are produced, they are still the smae species. If no viable offspring are produced, they are separate species. Interestingly, it seems to take very little gene flow between populations of higher organisms to prevent rep. isolation. Mutations are certainly a consequence of DNA replication, among other things. No process of chemical replication is without some probability of error, so yes, mutations are virtually inevitable. But keep in mind that only mutations in germ cell lines (eggs and sperm) will have any heritability.The other interesting thing about meiotic reduction of germ cells to the haploid state is that there is this wonderful mechanism of 'crossing over' . Chromasomes essentially lose their parental identity and genes of the mother become recombined with those of the father, and each egg and sperm, although carrying only a single copy of genes, carries an entirely unique arrangement of them. This seems to be an almost 'engineered' opportunity for creating new genetic arrangements. It also ensures that there is independent segregation of alleles - they are not inherited as whole bunch from one parent or the other.

That is correct.
You have all the key points clear.Meiotic reduction refers to the fact that all our cells have 2 copies of all genes (diploid) but when eggs and sperm are formed, they only get one copy (haploid) so that when they fuse together to form a zygote, the diploid state is restored. In terms of the chromasomes, for humans there are 23, but two copies of each in every cell (= 46), one from the egg the other from the sperm. What I am refering to here is that the copy of a particular chromasome you got from your mom, say no. 23, actually contains a mix of the genes from your maternal grandmother and maternal grandfather. Because of crossing over - the chromasome itself isn't inherited as a unit from either parent. Independent segregation refers to the fact that different alleles (alternative forms of the same gene) segregate independently because of this very mechanism. They have evolutionary destinies independent of one another in terms of the genotype they find themself in in the next generation. This mechanism seems eminently well 'designed' to create new genetic combinations every generation. (Please don't take the 'designed' literally).