reply to post by ACTS 2:38
First I have to say that I have NOT yet read the entire forum, I was just doing so when I saw your post and felt compelled to reply. If someone else
has already covered this, sorry.
The major issue which a lot (and I do mean a lot) of people have with understanding evolution comes not only from people [prats] like Richard Dawkins
who vocally pan religion as non-scientific, which understandably gets religious types riled (and actually, rejection without evidence is the
unscientific approach: there is no evidence that there is no god, and therefore to say that there is no god is an unscientific approach, etc.), but
also from the current classification system itself.
Current classification is based on the HIDEOUSLY limiting Linnaean classification of animals, in which he grouped them - for convenience, himself
firmly believing that every creature was created perfect by the creator - into discrete groups.
The problem is that a species does not "become" another. While progress may occur within a species, speciation is not (typically) by a "lizard giving
birth to a chicken", it is by the divergence of one population (not even specifically lineages) into two, and over MANY GENERATIONS, each population
accumulates its small changes and adaptations, and become GRADUALLY distinct from one another. Sometimes, the specifics of these adaptations limit the
re-combination of the two (or more) populations, and when this happens, you have two species.
As a hypothetical model for how this could happen, using vertebrate evolution, because it's generall the most straightforward, lets say that you
started with a goby type fish:
Say these goby-type fish were living originally living in fairly deep see, some way off the shore. As they are fairly successful gobies, their
population grows and members of it spread out until some of them end up in tidal waters. Eventually (fish weren't the first creatures in the sea so it
seems a safe enough assumption that there was something in it to eat them), a predatory species that usually lives somewhere else turns up and starts
eating the gobies in this new population, but it is quite big and so avoids going into the shallows where it can be trapped by a change in the tide.
The gobies that go into the shallows escape the predator, but themselves risk being trapped in small pools, which rapidly lose oxygen, when the tide
Those which get trapped in pools may eventually include some which can process the oxygen from air while the oxygen in the water itself depletes, and
thus not suffocate while they wait for the tide to come back in - obviously, these ones will have more offspring than the ones that died, and those
offspring are also able to stray further into the shallows, avoiding predators and also collecting their own food (e.g. light-loving micro-animals).
If their populations get big enough, competition may favour those who can even get out of the water a little way to reach valuable food that has been
moved out of their normal reach by the tide, and, through a series of lucky accidents, some of them become semi-terrestrial.
On the land, there is a lot less competition for everything, and so if you can stay out, you can exploit a whole new range of foodstuffs and have more
energy to put into food. This is not particularly different from the mudskippers of mangrove swamps at this point, and while they are not in the
ancestry of the amphibia, they have started along a similar path.
Anyway, as these animals are successfully exploiting this new niche and breeding like, well, mudskippers, they soon come into competition with one
another. An individual who is lucky enough to be less dependant upon moisture can access resources that aren't so heavily competed for, and so
increasingly terrestrial populations arise, and spread inland. They still, at this point, have to go back to the water to breed, but if one so
happened to develop a water-tight membrane for its eggs, then any eggs that happened to be washed out of the water would not be doomed. Any individual
losing the 'go to water to breed' response, if it had the water-tight egg genes, would not remove itself from the gene-pool by doing so, and its
offspring could gradually diverge from the water-breeding population (partially because combined the "don't breed in water" gene with the
"not-water-tight egg" gene could lead to disastrous results, so those that were selective in their mate choices would be better off)
So now we have our hypothetical reptilian, worlds apart from the ancestral hypothetical goby-type fish, not the same family at all, but still gotten
do to quite reasonably - I think. Of course, this would probably happen over a massive timescale, and a whole bunch of other changes (=mutations,
which if beneficial or just lucky can go to fixation (be omnipresent) in the population) would doubtless have occurred.
From reptiles to mammals is fairly simple - eggs are vulnerable to temperature changes, and so while some (modern) reptiles have eggs which are
relatively insensitive to these, or lay their eggs at times or in places where temperature remains optimal for the eggs to hatch, where constant
environments are rare, some reptiles keep their eggs inside them and move into warm places. Big eggs are cumbersome, and embryos start out small, so
anyone who happened to provision their developing young gradually (through a placenta type thing) rather than all at once (a shell-enclosed egg) would
be more able to avoid predators when carrying their young. Newborn young, with smaller bodies, are more susceptible to poor-quality environments than
adults, and so if parents provision these young in some way (e.g. milk), they will survive more reliably even when conditions are not favourable,
passing on the genes for provisioning to another generation.
Fur is just one of the many alternative approaches taken to allow activity/survival in colder climates: blubber, fur and feathers all keep heat within
a body, dark colouring and areas where blood vessels are particularly close to the surface allow heat to be absorbed more readily. Fur and (early)
feathers are both based on fairly straightforward mutuations of the DNA responsible for keratin production, which originally formed scales...
Most - and to my mind all - of what I've said so far could be considered 'micro-evolution', but when put together it can take you across the biggest
leaps in vertebrate "macro"-evolution. How is it difficult to understand that a change in time scale is the only thing required to bridge the gap?
Oh, and for humans (and remember both above and below are purely a hypothetical attempt at explaining it, and my intention is not to match up with
actual evolutionary patterns, but merely to suggest to those who feel otherwise that evolution could quite feasibly produce a variety of the forms
that we see today):
Once we've got our prototypical monkey, small bellies are all very well for digesting nutrient rich foods such as meat, but not so great for
cellulose-high plant material. A large gut is required to get the best out of relatively poor foods without resorting to coprophagy (like rabbits),
and for a large gut, you need a large body. Note that most herbivorous (excluding seen and fruit eating species) primates are quite large.
Once large, the prehensile tail that was so useful to small primates as an extra limb is no longer particularly useful, and so anyone losing it isn't
going to be particularly disadvantaged - to hold you on a branch if you fell, it would have to be a lot bigger, and it's not likely to get that big
fast enough to cope with the evolutionary requirement to stop relying on your tail to keep you from falling to your death.
Being large is alternatively useful to allow you not to starve: if you eat fruit, for example, and there are certain periods of the year where no such
fruit is around, being over a certain size means that you will survive until the next fruiting season.
So anyway, we have from apes to our big - and resultingly tailless - ape.
These apes are primarily arboreal, and when on the ground, move on all fours, which doesn't offer a great field of view but when you spend most of
your time up trees, this isn't really an issue. Anyway, along come elephants who like grass, that spindly little plant that typically grows up only
where trees can't or don't block out the light - and the elephants are happy to knock down trees to let their grass grow. Suddenly, there is a new
habitat, one which offers neither a vantage point nor a retreat: open grassland. As the big, frugivorous apes that live in the forests around these
spreading grasslands are dependant on getting a lot of fruit when it is available, they either have to change their diet, keep away from elephants or
get good at crossing grasslands. THose that do any of these will persist - those that don't go extinct, so we don't really have them to talk about any
So some of these now starving big, tailless apes start making regular trips across the grasslands to get to other food sources. They CAN go up onto
their hind feet, allowing them to see over the tall grass and tell whether any of their predators are in the way, but moving in this position is slow.
They are faster when on all fours, but they can't see so far across the open space, and so any predators that are lying in wait remain unseen until it
is too late, and so being able to move faster while upright will be selected for until we have an upright ape.
As the climate changes, and fruit trees become scarcer, living entirely on fruit becomes difficult for our plains apes, so they supplement their diet
- maybe by going to the water for slow moving invertebrate (shellfish) prey which are easy to catch, maybe by working in teams to bring down animals
that are too fast for an individual alone to catch. Of course, their upright position is not only good for watching out for predators, but also,
whenever they happened across the idea of throwing things at either predator or prey (which, trust me on this, is not unique to humans or even apes...
baboons are disgusting animals...), also meant that they had greater leverage and could throw harder. If they do start spearing the local wildlife,
however, they create a selection pressure on the local wildlife to stay further away from the upright apes, and so migrating away from their homelands
to places where the wildlife hasn't picked up on their throwing abilities is favourable if they are to continue supplementing their diet with meat. To
move further north, they need either to grow thicker fur (takes a long time if you don't have the genes for cold-responsive fur) or start wrapping up
warm. Otherwise they freeze.
So now that they have clothes and spears, do I really need to go on?
edit on 28-11-2010 by TheWill because: attack of the unwanted emoticons