real life wrote:
Well, either a species starts with 1 member.........
.......or you suddenly go from 0 to more than 1 (6? 10? 100? ......how many?).
But nobody seems to want to definitely commit to either explanation.
How many? However many there are in the population. Do you think that it's one single thing that changes overnight? I hope not.
http://www.abarnett.demon.co.uk/atheism/evolution.html#BIRTH
As a simple example, imagine a world that has deep oceans and warm, sunny beaches (much like ours). In the sea live some crabs. To begin with, these crabs can only survive in water a few feet deep. Their world ends where the tide washes up and down the shoreline - they can eat, live and breed only in the warm shallows. As there is more food in the warmer, sunnier waters near the beach, the crabs are driven there to feed. As the waves crash in and out, some will be washed up onto dry land, or stranded on a sand-bank as the tide goes out, and perish. Others might be able to survive just long enough to scuttle back into the sea.
This creates what is called a "selective pressure" on the crabs - natural selection weeds out those individuals unable to tolerate being out of water for prolonged periods. Those who can will be able to spend much more time on the shoreline - they will get the richer pickings, and they will have a greater probability of breeding and passing on their genes. Some of their offspring might not be able to last as long out of water as the parents, but others might be able to tolerate it a little more. Again, these will have a slight advantage in terms of feeding, mating and survival (they might be able to escape marine predators by climbing onto a dry rock). It becomes a positive feedback loop. The genes of those who survived longest and generated the most offspring will become more abundant in the population as a whole. After many generations, the crabs will be scuttling around on the beach, foraging for food, no longer restricted to a purely marine lifestyle.
Over time, different environmental conditions will shape different aspects of their bodies. They may come to rely on a particular type of food, or they shell may change in size and shape (to provide protection against the environment or predators). They will come to be radically different from their ancestors - a new species. They are, of course, still crabs - but they are a new type of crab, unable to breed with (or even meet) the species that they originated from. After a million years of separation and differing environmental conditions, these new crabs may have split further into a number of different, new species, or may have been changed into a type of creature that can no longer be called a crab.
Evolution is not a ladder - it's an enormous bush with millions of branches. We humans (and the chimps, gorillas and other apes) are just the current crop of leaves on part of the vertebrate/mammal/primate branch. As long as life exists on this planet, the bush will keep on spreading, and humans will be just one more branching-point with several new twigs growing from it.
