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Darwin's Descendants: Why Are Genes the Real Units of Natural Selection?
In the field of evolutionary biology, Richard Dawkins' book The Extended Phenotype sheds new light on the relationship between genes and their environment. Dawkins proposed that the phenotype of an organism should be further extended to the effects of genes on the environment, both inside and outside the organism.
"Genes not only affect the individual body, but also the entire ecological environment in which we live."
Genes as units of evolutionary selection
The central argument of The Extended Phenotype is that the real unit of natural selection is not the individual organism but the gene. Dawkins believed that genes are the actual units on which evolutionary forces act, and their success or failure determines whether genes can be replicated over many generations. These "replicators" are indirectly affected by natural selection through their "phenotypic effects".
Genes and protein synthesis
Dawkins pointed out that genes can directly control only the synthesis of proteins. Limiting the understanding of phenotype to gene expression within an organism is an arbitrary limitation that fails to reflect the effects that genes have on their environment through the behavior of the organism.
Genes may affect more than just an organism's body
Dawkins proposed three forms of extended phenotypes. The first is the ability of animals to use architectural techniques to modify their environment, such as mayflies' "houses" and beavers' "dams." The second form is the manipulation of other organisms. The morphology and behavior of an organism may affect not only its own adaptability, but also the robustness of other organisms.
"Some parasites are able to alter the behavior of their hosts to improve their own fitness."
For example, in some parasite-host interactions, the parasite can change the host's behavior to make the host more conducive to the parasite's reproduction. Dawkins cites the example of crickets that commit suicide by drowning, a behavior that is essential to the parasite's reproductive process.
Remote control of host behavior by parasites
The third extended phenotype is the parasite's ability to remotely manipulate its host. The common example Dawkins mentions is the behavior of cuckoo chicks, which can lure host birds to feed heavily. The host's behavioral performance is not directly linked to the individual parasite, but it affects the expression of its behavioral phenotype. .
“Animals’ behaviors tend to maximize the survival of the genes that underlie those behaviors, even if those genes are not present in the specific animal performing the behavior.”
Gene-centered view of life
In the book, Dawkins further reinforced the gene-centered view of the evolution of life and further challenged the interpretation of organisms. In his chapter "Rediscovering the Organism," he points out that the definition of an organism is not directly related to the selection pressure of genes. The influence of genes is not limited to the interior of the organism but extends to various interactions with the environment.
Reader's Reflection
The book "Extended Phenotype" undoubtedly inspired many biologists to think about the relationship between genetics and environment and guided subsequent research. The comprehensive expression of genes raises questions such as how do organisms modify the selective pressures of their environment during evolution? Does this mean that organisms are no longer the only units of evolution, but rather the result of co-evolution with the environment?
The extended phenotype concept proposed by Dawkins undoubtedly challenges the traditional way of thinking and makes us rethink the role of genes in the selection process. However, while thinking about these questions, we must also reflect: Can all environmental changes become advantages for gene survival?
