The use of gene editing technology to give humans the characteristics and abilities of different species, such as the underwater breathing ability of fish, is a very challenging idea that involves many complex issues. At present, it faces many limitations at the technical and ethical levels. The specific analysis is as follows： ### Challenges faced by technology realization 1. **Understanding of gene function** -Fish underwater breathing depends on specific organ and gene regulatory networks. To give this ability to humans, it is first necessary to gain an in-depth understanding of the precise functions of genes related to underwater breathing in fish and how they work together to realize the complex physiological process of underwater breathing. -For example, the gills of fish are the key organs for underwater breathing. Many cell types and genes in the gills are involved in processes such as gas exchange and ion balance. But at present, we are not completely clear about the details of the role of these genes in the entire physiological system, which increases the difficulty of accurately selecting and manipulating related genes. 2. **Gene editing accuracy** -Although gene editing technology can modify genes, it is very difficult to accurately integrate fish underwater breathing-related genes into specific locations in the human genome and ensure their normal expression and function. -Off-target effects may occur during gene editing, that is, other locations in the genome are edited incorrectly, which may lead to unexpected gene mutations and potential health risks. For example, when trying to insert a key gene into the human genome, it may be mistakenly inserted near other important genes, affecting the normal function of these genes and causing unknown physiological problems. 3. **Gene expression regulation** -Even if related genes are successfully integrated into the human genome, the problem of gene expression regulation still needs to be solved. There are differences in the regulatory mechanisms of gene expression of different species, and the underwater breathing genes of fish may not be expressed in the expected manner in the human cellular environment. -Human cells have their own complex gene expression and regulation network. To enable foreign fish genes to be expressed in human cells in a timely and appropriate amount, it is necessary to find suitable regulatory elements such as promoter and enhancer, and carry out fine regulatory design. For example, it may be necessary to construct artificial gene expression regulatory elements to ensure that fish underwater breathing-related genes can be correctly expressed in human lungs or other suitable parts, so as to achieve functions similar to fish underwater breathing, but the current technology in this area is still very immature. 4. **Physiological system integration** -Giving humans the ability to breathe underwater is not just as simple as making a certain gene express, it is also necessary to integrate this new function into the complex human physiological system. The human respiratory system, circulatory system, etc. are very different from fish. It is a huge challenge to coordinate the functions of underwater breathing with the existing human physiological system. -For example, the structure and function of human lungs are different from the gills of fish. How to transform the lungs or develop new gas exchange methods so that they can adapt to the changes brought about by underwater breathing, while ensuring normal interaction with other systems such as the cardiovascular system, there is currently no feasible solution. Moreover, the new way of breathing may have a chain reaction on the body's acid-base balance, energy metabolism and other physiological processes, which need to be comprehensively and in-depth research and solution. ### Ethics and Social issues 1. **Change the nature of mankind** -Genetic modification of humans to give characteristics to non-human species may cause profound ethical disputes about human nature and identity. Changing the basic biological characteristics of humans, blurring the boundaries between humans and other species, may affect traditional human concepts and values. -For example, once humans acquire non-human characteristics such as the underwater breathing ability of fish, this may lead to a re-examination of human uniqueness and dignity, and society may need to rethink fundamental issues such as what a true human being is and the moral status of human beings. 2. **Fairness and social differentiation** -Gene editing technology is currently expensive. If only a few people have the ability to use this technology to give future generations special abilities, it may exacerbate social injustice and lead to social differentiation. -The rich can afford to genetically modify their children to have special abilities such as underwater breathing, while the poor cannot reach them. This will further widen the gap between the rich and the poor and cause contradictions and antagonisms between social classes. Moreover, the unfair advantages brought about by this genetic technology may affect many aspects such as education, employment, and social resource allocation, and destroy the level playing field in society. 3. **Potential risks and unpredictability** -There are many potential risks in making such a major genetic modification to humans, and many of the consequences may be unpredictable. In addition to the technical risks such as off-target gene editing mentioned earlier, new genetic combinations and characteristics may bring unknown health problems and ecological effects. -For example, giving humans the ability to breathe underwater may change the body's immune response, metabolic patterns, etc., causing new diseases or health hazards. At the same time, if genetically modified humans enter the natural environment, they may cause unexpected damage to the ecological balance. For example, it may change the relationship between humans and other living things and affect the stability of the ecosystem. 4. **Ethical slippage and abuse** -Once it is turned on, the use of gene editing technology to change human characteristics