This is taken from a series of emails I exchanged with my brother over 10 years ago. He asked for explanation of why I didn't think animals don't/couldn't have a belief in life after death, e.g. in relation to dogs mourning their masters, elephant graveyards etc.
Lets look at the requirements for something or someone to have a spiritual thought:
You will need a constant idea of self. To think about what happens to 'yourself' after death, you will need a firm mental image of a self that will continue on. As I have said before, this mental picture is a construct that is brought about at the simplest level by the identification of "what is me" compared to "what is not me". This gives a starting point. A baby learns it can influence things in it's environment through effort (crying for it's mother, picking up a rattle) and builds a concept of the environment around it and it's own place in the system. Animals have this kind of self-image, and some animals have a very clear picture of the self and it's place. This is obvious in mammels like monkeys and apes, who have a very advanced mental image of the social structure of it's pack and it's own place in it.
The image of self is a mental image. It is a picture of what it means to be an individual relating to the outside world. This mental image won't usually directly correspond with others' idea of the person/animal. As the mental personality which has been constructed is an idea, the animal/person will build the personality through analysis of effects of it's own behaviour, consequences of actions and past experiences (e.g. a monkey who challenges the pack leader and loses with change his self-identity to view itself as weaker (at that time), which will influence it's behaviour to the others, and it's pick of the females). The personality will also be used to guess at the most likely course of action and to help better judgement in the future (bird gets attacked by a red snake it thinks is a big worm, it will then avoid big red things, etc.), although the personality is just a construct. Someone who is convinced he is tough and has a confident personality but has never been in a fight, etc... if that person is in a fight the personality image may guide his actions but the actions depend on how strong the self-image is in comparison to basic fight/flight drives. Animals probably have that level of self identity, but less structured and less reasoned than the self-image of humans... e.g. a small dog running in circles and barking at intruders is a classic example of the dog's confusion as it's self-image (protector of the house, aggressive animal etc.) clashes with it's instinctual drives (get the f... out of here, I'd lose the fight).
The self image also enables the individual to choose the right action in response to familiar stimuli... therefore kittens, lions, children etc playfighting will know that the threat is imaginary and will know their actions are only mock aggression. They will also put themselves in very vulnerable positions because they have identified the "enemy" as actually a friend (e.g. a lion exposing it's stomach or neck to the 'victor'). This activity is mock aggression but the idea is to go as far as possible to real aggression because the goal is to establish the social hierarchy and an individual's place in that hierarchy ("stop that rough playing or someone is going to get hurt").
Humans to a very high degree, and animals to a much lesser one, show selective recollection of past events. The difference is because humans have much better memories (and a much higher level of reasoning behind these memories) than animals. Therefore the person who thinks he's tough but backed down from a fight will imagine he acted braver, that there was more at stake, you know what I mean. A dog that pisses on the carpet will act embarrassed and scared of the wrath of the owner, but if the owner treats the dog well, it's behavior will resort back to being comfortable and confident around the owner.
Also, the self image is influenced by genetic commands, therefore a female lion will protect it's cubs at the expense of herself, but the male may eat them, pairs of puffins will take turns sitting on eggs and many birds will form a lifelong bond while some species will not. Up to this point it's clear that the drives and the self-image are shared by humans and at least the higher animals - the difference is only in the complexity of actions and thought processes. That brings us to:
The relation of the individual to others is influenced very much by the behavior of others to it's actions - the whole nature/nurture argument. Self image in a social animal is based on one's place in the social group. From birth an individual is taught to behave in a certain way by selective reward/punishment from it's peers and elders - it learns certain behaviors are good or bad. This is where the use of language and the transfer of information becomes important. Some mammals (and some animals) have complex languages - because of their simpler behaviour (in relation to human's), these languages are concerned with giving directions and the transfer of geographical information (the bee wiggle dance, whales singing(probably)), the hunting and gathering of food (apes using sticks to fish for termites and teaching the young, the calls and codes of packs of dogs/jackals etc when hunting), the signal for sex (crickets, birdsong etc.) and the identification of danger (warning signals in group animals).
The human brain is (in my strong opinion) to look for patterns. This is evident in not only babies' inborn sense of rhythm and perception of visual patterns, but their ability to pick up social rules and the subtleties of language. From an early age though, cultural influences come into the equation. I read a few days ago that tests have shown all babies have perfect pitch, that is they can identify the pitch of a singular note without help. Nearly all adults have relative pitch, which is we can only identify notes in relation to others. The loss of perfect pitch is an important one because otherwise, you wouldn't be able to recognise that "happy birthday" sung by a woman and then a deep-voiced man are the same song, or be able to recognise different uses, pronunciations and octaves of spoken language.
Babies are more confident when there are patterns, and human culture enforces this by encouraging predictable, pattern-based behaviour and thinking. This gives rise to a child's curiosity. The child begins to be hungry for the pattern and wants to see the structure that seems so obvious to adults. This is the little kid "but why" stage. "Why do I have to eat my greens", "otherwise you'll be sick", "why will I be sick", "because greens are good for you", "why are they good for me?", "because they have vitamins", "why do vitamins taste so bad?" etc etc. Most of these conversations end with the adult saying "because I said so ok", or "just because". This is the adult communicating that the conversation has ended and signals that the adult forms the "end of the equation", or that the adult holds knowledge but will not impart it on the child. This "but why" stage therefore reinforces an authoritarian view and the cultural structure because all questions inevitably lead to the adult's choice that "that's just the way it is". Also, because most cultures are founded on religious ideas, many but why's will lead to religious foundations - "because God can do anything", "because Jesus loves us", "Because that is the fifth commandment", "because if you do that you will go to heaven" etc.
It may be possible that animals have this "but why" stage. It's probably common because curiosity is very important. A cub will play with scorpions until it gets stung or it's mother cuffs it round the head, it will attack its dad's ear until it gets another cuff or a bite. But animals don't have the complexity of language that we do. The amount of information they can impart is the equivalent of "food", "sex", "danger" etc. Pack animals have more subtle means of communication and can transfer more complex information, but not much info. is transferred from one generation to the next so there is not much chance of the information and language itself to evolve and get more complex. Put simply, there are less steps to take when the baby is building a world-perception before it leads to the adult "because I said so" (cuff around the head) stage. The difference from the human behaviour is the complexity of explanations. Religious thought (and spiritualism to a lesser degree) is the result of cultural influences and an evolution of ideas, myths and stories being transferred over generations to build a cultural explanation of the "but why"'s that aren't immediately obvious to the culture at the time ("but why does it rain", "but why are the gods angry?", "but why does the sun rise?", "but why is there life on earth?"). As you have said, religion is impossible without the need for information transfer over long periods of time, that's why there'll be no elephants doing ritual sacrifices.
Cultural ideas are very biased toward the view that the 'self' is something definite, a soul or actual thing that reacts to stimuli. But this is not backed up by evidence. A person's self is structured by experiences and although a person may think they project an idea of how they "really" are, this may not be backed up by observers. Also, a person's idea of what type of person they are and predictions of their behaviour in certain situations will often be very different to their thought patterns and behaviour when they are actually faced with the situation, instead of the fantasy. But still, the cultural idea is that the "self" is a pilot in charge of the body, something that reacts to the environment and may be shaped by it, but not bounded by it ("that's not really me talking", "I'm trying to just be myself") - to an extreme you can see this in the Nazi argument of someone "just following orders".
This cultural idea of the self is backed up by ritual (diaries, self-expression/art etc.) that identify the self as a pristine thing, to myths and stories of a soul/pilot of the body, a separation of the self from the other, where the body also becomes the 'other', the environment that the "real self" is reacting to. By natural habits of selective perception/recollection, the self-image is strengthened ("I could've kicked his ass, he sucker punched me", "I only freaked out cause I hadn't read the recommended text"). Does this manifest in animals? maybe in the very intelligent, domesticated ones (ones that therefore have an unnatural level of stimulation and cultural reinforcement. E.g. a dog who pisses on the carpet then puts it's tail between it's legs and hides knows it did a bad thing and it "shouldn't have done that", so has a perception of right and wrong and knowledge of it's own actions. However, I can't at the moment think of examples in the wild where animals show this level of perception and it could be argued that they don't (but it is clear they have the potential to show a primitive form)). Because the cultural norm is very much the idea of a 'real' self, it is a small step to consider that the self is a separate entity entirely from the environment/body, and that the "real" self (that is the mental image of the self that may not be supported either by behaviour obvious to others, personal actions or personal, subjective thought processes in the real world (by real world I mean (e.g.) the environment (e.g. future) where the individual has fantasized the action will manifest) will survive after physical death. I will get to the difference between that, human, thought and animal thought soon.
The influence of these cultural answers to the individual's self-perception will cause the individual to form a certain picture of the world and of it's own place in the scheme of things. But this perception will be very much controlled by the cultural information imparted. We have the same brains as we had 40,000 years ago. Stone age man had basic (maybe earth-based, shamanistic) spirituality but nothing like today's organised religion, which has needed to be built up over thousands of years. The fact that there is the potential for certain thought doesn't mean that this thought will be present. An animal may have a brain structure capable of learning complex behaviour, but this behaviour will only come into effect as a result of what information the animal is able to process from the environment and other animals (police/guide dogs, show ponies, apes learning basic sign language - these are all domesticated animals who have learned complex behaviour by benefiting from learning the evolved social and cultural patterns of humans).
I have said that our human cognition is a result of our ability to transmit very large amounts of information from one individual/generation to the next. Because each individuals experiences (therefore perceptions, ideas and personality) will differ, the transfer of information will result in questions of the way things "really" are (again, the "but why"'s). As humans, we are in a unique position because we have evolved complex methods of communications (the reasons I have given before (an intelligence arms race since because our greatest threat has been from other groups of humans with generally the same traits, the greatest weapon has been a greater intelligence, therefore a greater group bond, weapon/tactics ability etc)) that we can transmit to others (because of our social nature language has developed, as it has with other animals, but our language is complex enough to transmit highly structured ideas (self-images). We also live far longer than most comparable (i.e. intelligent, pack) animals, so our individual personalities and our ideas of self and our place in the world will understandably be much more complex.
Because we have a much more structured culture and information transmission capability than other animals, one result is that we can directly compare ourselves to many others, we can compare minute details of our own thinking and self-image with those of others, and we have not only our direct group companions to choose from, as animals do, but thousands of other people (and therefore wildly diverse cultures and self-images). This will not only make us consider our own self image much more closely, but it will also reinforce our own perception of what our "I" is.
You have said that other animals have time to contemplate their existence. I don't believe other animals do for many reasons but I'll talk about this point anyway (because you brought it up).... even if they had the potential for that thought, think about those times they would have the "opportunity" - a solitary animal has to be constantly hunting for food or protecting the stuff it has, or finding safety etc, because it's survival depends on it's every action. There's no group to support it if it becomes injured or too tired to hunt, it's dependent totally on itself. Considering there is a constant survival of the fittest, I think the animals that would survive would be those where every waking moment is devoted to survival drives. Lets look at ones with more time, pack animals where some can be lazy and still survive. With most pack animals, all possible time is spent either hunting etc, or enforcing the pack hierarchy and structure. Think about the animals with the most contemplation time - they are the heads of the pack, the bull elephants/seals, the head lion of the pride. The point of being the head of the pack is to get the best females, so that's why he spends every possible moment shagging. The lion/elephant/seal... will need to be always on the lookout for a challenge to it's status from younger group-members, so will need to pay attention on establishing it's dominance. If an adult human (with the benefit of an education and a spiritual background) was given a lion suit and the position of head of the pride, I think even he would have trouble contemplating the meaning of life instead of f...ing as much as possible (eugh!), sleeping, eating and fighting, all of these which take up precious energy.
To wonder what happens to the subjective construct of "self" after death, it's obvious you need an understanding of death and an awareness that the body can die. As I have noted before, spiritual ideas of the soul surviving after death are a very recent construct (probably the last 4,000 or so years) and have required thousands of years of advanced human thought and information transmission to develop to that point. Before that point, myths and ideas of death and the spiritual realm were bounded by the earth. Cavemen burial sites and Egyptian pyramids were filled with physical objects (sometimes even slaves, food and weapons) that the dead person would be able to "use" in the next realm. The inclusion of symbolic relics (a stone army for a Chinese Emperor, trinkets, talismans) is a step up from this but the train of thought was still that the dead person would require the same kinds of things (food, weapons, slaves) in the next life - it was just that those things were supplied in symbolic/incorporeal form because the individual was now seen as the symbolic/incorporeal.
Animals are concerned with the here and now. They seldom, if never plan ahead for possible future events, unless the events are linked to the here and now (build nest because the birth is coming, trek for water/warm weather because you are thirsty/cold). The understanding of death is a complex one and one that has required thousands of years of advanced human understanding. The perception of an animal of an other is linked with the sensual responses it receives from that other, that is why you can make a mother sheep adopt a new lamb by draping the lamb in the skin of the dead one. An animal's perception of an 'other' is directly linked to the other's actions and whether they are familiar.
An individual would need to have a perception of death. An animal has a perception of sickness/weakness and may see others die but their perception of the dead animal is bounded by it's body lying there. Once another drive (food, heat etc) replaces the drive to stay and care for the perceived sick animal, it will leave. That doesn't mean it will forget about the dead animal but the perception of it will be bounded in the physical presence and the location of it's smell etc (a mother looking for a lost lamb).
The animal would then need to take the perception of the death of the animal and turn that perception around to itself to be able to understand the possibility that it is able to die. This would require an understanding that others have the same self-perception as itself. Now, if you look at Piaget's experiments with children and the stages of development, it says that up to the age of around 4 or 5 (at least) a human child is unable to comprehend the fact that other people have their own subjective reality (e.g. saying to a child "draw that car", then saying "draw the way you think Tommy over on the other side of the car sees the car"). That is why they say in experiments with teaching apes to 'talk' through sign language, that they can only reach the mental sophistication of a small child, in that that mental stage of development is quite a sophisticated one.
It would also require an animal contemplating that if the circumstances were right and it didn't get enough food/was attacked etc, then this would happen to itself. This requires foresight and vision of using the (above) established and sophisticated perception that others are a separate "self" as well, and then constructing an alternate (imaginary) reality where circumstances would cause the individual to die itself.
So there you are. Animals lack:
· The opportunity to construct a complicated and definite, culturally sanctioned view of a self that is separate from the body, (they may have a very basic one).
· Foresight into the consequences of their actions beyond the basic (although they may exhibit hindsight).
· Sufficient complexity of memory to both construct the self-identity and to reinforce that perception through selective recollection.
· A social structure where complex concepts (that need to evolve over a generations) may be transmitted to them. Humans have the advantage because of their social structure, free time, advanced language processing, quick learning, information transmission ability, and long life.
· The ability to consolidate their self-identity because they lack the access to all the above, plus complex understanding of the possibility of different cultures, and the differing self identities of many others beyond the immediate pack.
· The possibility to understand complex patterns because of the redundancy of their information transmission/processing ability (although they may hunger for patterns and be curious).
· A complicated, evolving social structure where ritual and belief could result. Although they may have the potential for complicated perception they are limited to the knowledge pool of their current peers.
· The time to contemplate existence that humans have. Although some animals can relax more than others, group dynamics and the pressure of Darwinist survival means thought must be devoted to primal drives.
· An awareness of the reality of death itself, because that awareness requires a perception that others are made up of individual self identities and have different perceptions.
· The understanding of death of self, which also requires imagination and vision of an alternate possible future where circumstances would cause the death of the self.