Annie ji,
At the risk of sounding like a nut... I believe in reincarnation because I have an instinctive feeling about it, and because I have seen things. I believe in it because some of us seem to be much older and more mature than others spiritually, and it can't always be explained by our environment.
I think that you are correct in concluding that there are things which can't be explained in terms of environmental influence, and that we are who we are due to influences that go back to past lives. However I think that we need to be precise about such things, because otherwise we will just mix causes with effects which then leads to doubt and moving up and down between belief and disbelief.
My feeling about transmigration is not as strong, but it sort of makes sense to me. If we have souls, animals must too; and we must have been something other than human if our souls were around before human bodies began to exist on Earth.
I don't believe in reincarnation or transmigration. This is because I don't believe in the existence of a soul. What I believe is that all there ever is are mental and physical phenomena, and apart from the unconditioned Nirvana, these are conditioned and extremely fleeting. I believe that one of the features of mental phenomena, which include consciousness and its mental concomitants, is that they are accumulative in nature and when they fall away, immediately conditions a next instance of consciousness on and on, never to stop (until one becomes fully enlightened and pass away). This is what happens now and is reason why death must be followed immediately by rebirth consciousness.
What happens after death is therefore not reincarnation or transmigration, but "rebirth". It is rebirth because what one is born as, is determined by the karma which arose just before the dying consciousness of the previous life. This means that if the karma is unwholesome, one will be born in one of the lower planes of existence and if it is wholesome, it will be in one of the higher planes. So yes, we do come with *all* that we have accumulated from the past including both good and bad tendencies. And it also means that our life from one to the next is never in linear progression, but move up and down between plains of existence. Although when born as an animal, the probability of going up is exponentially reduced due to their inability to distinguish good from bad and right from wrong.
So I think that you should take care not be moved by the idea that at one time on earth there were no human beings, and also not let the concept of evolution confuse and mislead you. This is because they are stories only about "earth" and earth is not the only place where life exists, and the 'human form' as we know it, is not necessarily the only one which supports that particular kind of good karma. Indeed, animals share the same planet as us, but their plane of existence, unlike ours is one which is the result of an altogether different kind of karma! So we need to think in terms of planes of existence and planes of consciousness, rather than that of evolution of life in this particular planet.
Um... karma. I think it is when we give the idea too much power and detail that it begins to sound ridiculous.
It sounds ridiculous only if we try to comprehend it from the standpoint of the existence in 'self' or 'soul'. When we think in terms of a self who acts and who receives the fruits of his or her actions and are not precise as to what it is that are causes and what the results, we will end up confusing things. The problem is not in the details, but often it is in the oversimplification. Yes, it is wrong to speculate about karma and wonder about such things as 'what might be the cause for this result' or 'what kind of fruit will this action bring', because this again is due to the influence of "self" and is blinding. It comes from wanting to know and to control and predict, and is why it is said to be capable of leading to madness.
However on the other hand, if we are vague, this can lead to mistaking causes for results and vice versa and this too is wrong.
Allow me to give some examples:
A misfortune is often referred to as being the result of bad karma. Now although this is true since a misfortune can be seen as coming down to unpleasant experiences through the five senses, most people however are caught up in a story about 'someone being in a particular situation'. This perception when taken seriously can lead to mistaking for example, sadness as also being result of karma, when in fact it is not. Sadness is actually the stuff of cause and not of result. And with this perception, there can't be any understanding and as often is the case, leads to feeling of deject where the whole thing is seen as fated.
Similar to this situation is when people refer to their inclinations to good and bad and general habitual tendencies as being due to karma. This again is wrong, since karma is actually the mental factor of intention arisen with the consciousness. One's inclinations changes each time that a new action takes place. So in seeing the accumulated tendency as karma, this too can lead wrongly, to feelings of helplessness.
Reacting to the above misunderstandings, some may feel inclined to interpret karma and rebirth, in a way that I once did. When it is said that good karma leads to heaven and bad karma leads to hell, we think that this means for example, that a good state of mind is free of agitation and is akin to being in heaven, likewise when we are say, angry, this is a state of agitation, and is like being in hell. We resist the idea that there is a life beyond this one and so the inclination is to interpret the concept in terms of what we are willing to accept. But clearly this is very misleading.
The reason being that what we refer to as being results, i.e. the states akin to heaven and hell are in reality, the pleasant feelings that accompany either a wholesome state of mind or that which accompanies attachment. And these are "causes" and not "results"! This means that in our resistance to the concept of karma and rebirth, we have come to take for resultant consciousness what in fact is a cause, and this is wrong understanding. And what may then follow from this is an inclination to judge as worthy of pursuit, states of mind accompanied by pleasant feelings, which in our case must be "attachment". And so we see people judging success or failure in their pursuit of religious ideals by how happy or blissful they are. And this is what they try to make increase which must then be planting seeds that will result in the experience of unpleasant objects in the future. And isn't this a big trap?
What if karma is simply a natural law of cause and effect? If you work to improve the world, the world will be that much nicer for you and others. If you are a jerk, people will be jerks to you. And maybe we are here in the circumstances we are born into, to learn something we could never learn otherwise.
This is an example of what I was saying above. Surely you've heard about good people suffering while bad people getting away with what they do haven't you? So I don't think it right to interpret karma the way you have done. We do what we do, good or bad, according to our accumulated inclinations and other conditions. Likewise how other people react is *not* a result of our actions, but their own accumulated tendencies and other conditions at any given time.
Praise / blame, pleasure / pain, gain / loss and fame / disgrace are the eight worldly conditions we all face. True a good person will more likely than not be praised for it, but this is not a result, but because most people see the value of goodness and some of them then express praise while others may not.
The bottom line is that I really know nothing. I don't even know WHY our existence is so hard to understand. I can only hear other people's ideas and try to do what seems right.
The Truth remains hidden because of the overwhelming tendency to ignorance. To recognize ignorance is a step in the right direction. But as in the case of karma, first we must understand what ignorance is and what is it that ignorance is ignorant of, because otherwise we will go the wrong way.
But I won't start to talk about this here. ;-)