There are several reasons why more complex organisms are less able to give rise to new individuals through regeneration:
- Complexity: More complex organisms have a higher number of specialized cells and tissues, making it difficult for them to regrow lost or damaged parts.
- Limited regenerative capabilities: Many complex organisms have limited regenerative capabilities, meaning that they are only able to regrow certain types of tissues or body parts, and not others.
- Control mechanisms: In more complex organisms, there are multiple control mechanisms that regulate cell division and differentiation, which can make it difficult for cells to divide and differentiate in the correct way for regeneration to occur.
- Aging: As organisms age, their ability to regenerate decreases, and this is more pronounced in complex organisms because of the accumulation of damage and deterioration of their control mechanisms.
- Lack of blastemas: In many complex organisms, cells do not form blastemas, which are undifferentiated masses of cells that are able to differentiate into the various cell types required for regeneration.
- More complex developmental process: Complex organisms have a more complex developmental process, which makes it difficult to reverse the process and go back to a more primitive state to regenerate.
Overall, while some complex organisms like certain amphibians, fish, and some invertebrates have some regenerative capabilities, it is limited and not as efficient as in simpler organisms.