Once cancer cells develop within the body, selection favors their proliferation even though this ultimately may lead to the death of the individual and the cancer cells. What explains this short-sighted evolution?

The phenomenon where cancer cells proliferate within the body despite the potential for leading to the death of the individual, including the cancer cells themselves, can be explained by the concept of "short-sighted" or "myopic" evolution. This concept refers to the idea that natural selection operates on the level of individual cells or organisms, favoring traits that increase their immediate reproductive success, without regard for the long-term consequences for the individual or the population.

Here are several factors that contribute to this short-sighted evolution in the context of cancer:

1. **Somatic Evolution:** Cancer cells undergo a process of somatic evolution. Unlike germline evolution, which concerns changes in the genes passed on to offspring, somatic evolution occurs within the tissues of an organism during its lifetime. Cancer cells acquire mutations that confer a selective advantage within the tissue ecosystem, allowing them to proliferate more than their normal counterparts.

2. **Clonal Selection:** As cancer cells accumulate mutations, those with the most advantageous traits for survival and reproduction within the local environment will expand in number. This is similar to natural selection in a population of organisms, but it occurs at the cellular level within the body. Traits that enhance cell division, evade the immune system, or resist cell death signals will be selected for, even if they are detrimental to the organism as a whole.

3. **Lack of Foresight:** Evolution does not plan for the future; it is a process that selects for traits that are beneficial in the present moment. Cancer cells do not have foresight or the ability to consider the consequences of their proliferation. They are simply following the basic biological imperative to survive and reproduce.

4. **Genetic Instability:** Many cancers are characterized by genetic instability, which leads to a high mutation rate. This increases the likelihood of developing mutations that can confer a selective advantage, accelerating the process of somatic evolution.

5. **Resource Competition:** Within the body, cells compete for resources such as nutrients and space. Cancer cells that are more efficient at acquiring resources or that can thrive in less-than-ideal conditions will outcompete normal cells.

6. **Escape from Regulatory Mechanisms:** Normal cells are subject to a variety of regulatory mechanisms that control cell growth and division. Cancer cells often acquire mutations that allow them to escape these controls, giving them a growth advantage.

7. **Microenvironmental Influences:** The tumor microenvironment, which includes the surrounding cells, blood vessels, and extracellular matrix, can also influence the evolution of cancer cells. Factors within this microenvironment can select for more aggressive cancer cell phenotypes.

In summary, the short-sighted evolution of cancer cells is driven by the immediate selective pressures acting on individual cells within the body. These cells evolve to survive and proliferate in their local environment, without regard to the long-term survival of the organism. This process is a consequence of the basic principles of natural selection and does not reflect a conscious strategy or long-term planning.