1 Nonconscious life and its emotion
Although the human is such a complicated life system, it evolved from more basic life systems and still share many features with those systems. Understanding of the human requires understanding of basic life systems. We start from nonconsious life systems
Any life system faces 'objects'(anything that is detectable by a life system) that come from its 'environment'. The environment, being defined as what is NOT the system, contains all sorts of changes, but most of them are not detected by a life system as its 'objects' (for example, I do not detect almost all of the molecular movements in the air). However, some changes are detected even by a single-celled organism. The detection is an advantage of a life system in comparison with a non-life system (a stone, for example) because a life system detects changes (i.e., objects) that affect its life. The detection of objects increases the chance of survival in its environment.
The detection of objects is represented internally so that the life system can use the representation for starting its own movement (the movement of a stone is only dictated by the physical law, whereas a life system can react on its own). The internal representation is about motions (=changes) in the body of the life system and Damasio called it 'emotion' (to avoid confusion, I'd prefer to use a technical term such as 'e-motion', but I'll follow Damasio's terminology). The detection is represented in the nervous system of the life system, constituting its first-order neural pattern. By 'feeling' the emotion (i.e., the first-order neural pattern), the life system can initiate its own reaction (or action) for its survival.
This concept of the detection of objects, incidentally, corresponds with the definition of information by Bateson: 'a difference which makes a difference.' Finding objects (information) is important for a life system for its survival. Information detection should be selectively improved (i.e., to detect all but only information that is critical for the survival).
To increase the chance of survival further, it is advantageous for a life system to be 'aware' of the detection, and still more, to keep the record of the awareness internally for potential future use. This is why, I assume, some life systems evolved to have consciousness and memory.
2 CORE CONSCIOUSNESS AND CORE SELF
Life systems that have been evolved beyond the level of detecting information (i.e., its objects in its environment) to be aware of (or to know) the detection so that it can better be used in future are those that have consciousness, or to be more exact, 'core consciousness' in the terminology of Damasio.
Basic life systems that are only at the level of detecting information just react automatically. If the environment is stable and regular, this automatic reaction should be sufficient. However, if the environment is quite changeable, or if a life system is to explore more into its environment, a life system should not just react automatically but also be conscious of the detection and reaction. As the detection and reaction is of the first-order neural pattern, being conscious of (or knowing) the detection and reaction is of the second-order neural pattern; The first-order neural pattern makes the detection and reaction possible, and it is the second-order neural pattern that makes possible consciousness or knowledge of the first-neural pattern.
This second-order neural representation of core consciousness is the source of the sense of self, or 'core self' according to Damasio. And as core consciousness (the second-order neural representation) is based on the first-order neural representation, which is ultimately based on (the detection of) objects in the environment, we may argue that our (core) consciousness is first initiated by our environment (although, of course, it is made aware of by the functions of our internal life system). -- Is this emphasis on objects in the environment related to the argument about intentionality by Brentano and Husserl? --
The sense of core self emerges in us because of the role of core consciousness. If something is not only detected but also known (or made conscious), there should be something that serves as the subject of knowing the object. Furthermore, if some new (re)action is produced from the knowledge (or the consciousness), there should be something that serves as the agent of the (re)action. Something that serves as the subject/agent emerges in the life system. (Here I may be introducing a normative metaphysical argument into what should only be a biological discussion. But how can we discuss biology or indeed anything without metaphysics?)
The core self equipped with conscious knowledge of the detection and reaction now maintains this second-order neural representation for its better chance of survival in future. This is memory, and as this memory is built through its own experience, this memory is called by Damasio 'autobiographical memory'.
Autobiographical memory is maintained presumably even by some non-linguistic animals like dogs, because dogs remember their experience and learn to react differently from the past. However, an animal that uses signs can encode (to a varying degree) its autobiographical memory into the signs and use them for itself, and perhaps more importantly, exploits the signs made by other animals for its own advantage. Autobiographical memory, at least some part of it, is now extended beyond one animal to its community by the use of signs. The typical animal that uses signs is of course humans. In the next section, I'll explain the new type of consciousness and self ('extended consciousness' and 'autobiographical self') that humans have acquired mostly but not exclusively by the use of language. (Although there are other signs than language, I'll focus on language in the next section because it is the typical and most powerful sign).
3 EXTENDED CONSCIOUSNESS AND AUTOBIOGRAPHICAL SELF
Language expands our horizons. With the use of language, we more explicitly recall the past (of ours and others'), imagine alternative realities of the current situation, and rehearse possible scenarios for the future. Our consciousness is now beyond 'here and now' of core consciousness and extended into possible realities. Damasio calls this type of consciousness 'extended consciousness'.
Below is my summary about Damasio's different types of consciousness and self. I haven't introduced the term 'proto-self' above to make the argument simpler. But its meaning should be obvious from the table below. I should also mention that there can be non-linguistic extended consciousness (for example, by the use of non-linguistic signs). However, as the use of language is almost ubiquitous in our mental life, I described extended consciousness as "linguistically conscious" in the table below.