Humans generally do not have memories of their infancy due to several reasons related to brain development and memory formation:

1. Brain Development: The brain undergoes significant development during infancy. The prefrontal cortex, which is responsible for higher cognitive functions, including memory formation and retrieval, is not fully developed until around the age of 2 or 3. This part of the brain is crucial for creating and storing conscious memories.
2. Memory Consolidation: The process of memory consolidation, which is the transformation of short-term memories into long-term storage, is not fully operational in infants. The mechanisms that allow for the stable encoding and retrieval of memories are not yet mature.
3. Lack of Language: Language plays a critical role in memory formation and retrieval. Infants have not yet developed language skills necessary to create narratives or conceptual frameworks for their experiences, which are important for memory storage.
4. Sensory Perception: Infants’ sensory systems are still developing, and their perception of the world is different from that of older children or adults. This difference in perception may affect the encoding of memories.
5. Emotional Regulation: Emotions are closely tied to memory, and infants’ emotional regulatory systems are not as developed as those of older children and adults. This could affect the salience of events and their subsequent encoding into memory.
6. Social Interaction: Memories are often formed through social interaction and storytelling. Infants have limited social interactions and are not yet capable of participating in the types of conversations that facilitate memory recall.
7. Primitive Survival Mechanisms: Some theories suggest that the lack of infant memory may be a survival mechanism. If an infant were to remember negative or distressing events, it might affect their ability to bond with their caregiver, which is crucial for their survival and development.

It’s important to note that while adults typically do not have memories of their infancy, some individuals may have “infantile amnesia,” which refers to the inability to recall events from early childhood. However, this is different from having no memory formation at all during infancy. Some memories from early childhood can sometimes be recovered later in life, often under hypnosis or other therapeutic techniques, but these memories are often controversial and their validity is debated among experts.