kennythebomb
With that said I also believe in micro-evolution, which is obviously proven, but not macro evolution except in maybe rare instances.
The processes involved in micro-evolution and macro-evolution are the same, in other words, if you accept the evidence which proves that micro-evolution can and does happen, then it follows that you must also accept that macro-evolution can happen. Micro-evolution, as I understand it, is the principle by which certain properties of a species are adaptable, such as the camoflague of a stick insect (like I mentioned above), or longer necks for giraffes etc. The evidence for micro-evolution is plentiful and (as you point out) is not in question. However, if you accept that it happens, then what is the reasoning behind putting constraints on it? In other words, when does micro-evolution stop? The answer is that is doesn't. Take an island covered in all sorts of different creatures - and take one example, say a monkey of some description. That population will interbreed and micro-evolution will occur... But what happens when, for some reason (rising sea levels, changing shape of the land by volcanic activity etc.,) causes the island to split into two physically separate regions?... each half of the population is now incapable of breeding with the other. The gene flow between the two halves has stopped. What happens next is that any genetic changes in one half of the population is now no longer followed by the other. Over the centuries, the two halves of the population, once genetically indistinct from each other, are now distinct. And one result of this genetic distinction means that they are now no longer able to successfully breed with members of the other population. From the common ancestor (when the two halves of the population lived side by side), arises two, genetically distinct populations of animal...
Even in this simplistic example, you can see how speciation (and hence macro-evolution) may occur, simply as a result of geographical separation. In reality, this may occur many many times, and there are many other mechanisms that may also result in speciation (not least the fact that the evolution of any one species is interdependent on the evolution of many others... thus small changes in one species will lead to small changes in an other, for example, faster foxes will lead to faster/smarter rabbits etc.)...In the geographical separation example, the separation would not need to be so cut and dried as a
complete physical separation... given enough land, and a propensity for territoriality (like most animals have to this day), speciation may occur without the need for total physical separation. You may point out that in that example, what you end up with is two sub-species of monkey, as opposed to any completely new species... but it depends on what you classify as a 'species', which in itself is a vexed question. The observation, however, that distinct populations of animals can be traced back to common ancestors, lends heavy support to the theory of macro-evolution , although micro-evolution is even better evidence if you ask me... given enough iterations of small change (micro-evolution), and without constraints (i.e. time on a geological scale), hey presto, you have changes on a large scale, or macro-evolution...
An interesting issue, related to this, is that of the origins of different human races - our modern understanding of this issue is inextricably linked to our modern understanding of global plate tectonics and how the land mass of the Earth separated into distinct continents etc....
This picture of continental drift, provides a large-scale example of how geographic separation of species occured, and suggests how subsequent macro-evolution of species could have been facilitated.