{"id":174,"date":"2013-11-18T16:41:16","date_gmt":"2013-11-18T16:41:16","guid":{"rendered":"http:\/\/joshmitteldorf.peachpuff-wolverine-566518.hostingersite.com\/?p=174"},"modified":"2013-11-19T03:50:40","modified_gmt":"2013-11-19T03:50:40","slug":"the-selfish-gene-vs-multi-level-selection-aging-doesnt-fit","status":"publish","type":"post","link":"https:\/\/scienceblog.com\/joshmitteldorf\/2013\/11\/18\/the-selfish-gene-vs-multi-level-selection-aging-doesnt-fit\/","title":{"rendered":"The Selfish Gene vs Multi-level Selection: Aging Doesn\u2019t Fit"},"content":{"rendered":"

This is the first of two parts on the history of evolutionary theory. \u00a0First came neo-Darwinism, popularized as the selfish gene<\/a>. \u00a0Genes are evolved to promote their own replication, and also copies of themselves that exist in relatives. \u00a0In the 1970s, the theory was extended by George Price to deal rigorously with groups that may or may not be related. \u00a0This is now known as multi-level selection (MLS). \u00a0There is an ongoing dialog in the evolutionary community about whether MLS is significant in nature, which is still the minority view. \u00a0The majority continues to hold that everything should be explainable in terms of the selfish gene. \u00a0But aging cannot be explained by the selfish gene; and even with the considerably broader perspective of MLS, the evolution of aging remains problematic. \u00a0What is missing from both systems is ecology. \u00a0When species\u2019 interdependence is taken into account, it becomes possible to understand aging and many other cases where individuals sacrifice their own fitness to the community.<\/em><\/p>\n

Darwin\u2019s theory was descriptive and qualitative. \u00a0Sixty years after Darwin, A British mathematician named Ronald A. Fisher<\/a> proposed the first fully quantitative model of how evolution might work.<\/p>\n

In the 18th and 19th Centuries, the science of physics had advanced through reductionism: dividing systems into their constituent parts, and demonstrating that each part obeyed simple, universal mathematical laws. Fisher wished to do for biology what Newton and Maxwell had done for physics. \u00a0Physics built everything from simple point particles. \u00a0Fisher asked himself, what are the atoms of evolution – the irreducible elements from which he might construct a theory.<\/p>\n

In populations of bacteria, Fisher might have taken the individual as an atom of inheritance. \u00a0Individual bacteria make exact copies of themselves, and the number of copies might be taken as a a measure of the individual\u2019s success in evolutionary competition. \u00a0But in sexual populations, no two individuals are alike. \u00a0What is the \u201catom\u201d of evolution for a sexual species?<\/p>\n

 <\/p>\n

In search of the \u201cAtom\u201d of evolution<\/strong><\/p>\n

Genetics was yet a new science in 1920, as Gregor Mendel\u2019s breeding experiments in the mid-19th Century had just been rediscovered, and their importance for evolutionary science was first appreciated. \u00a0In 1909, Danish botanist Wilhelm Johannsen<\/a> had coined the word gene<\/a> to describe the theoretical unit of inheritance. \u00a0(Of course, it would be another 20 years before Erwin Schroedinger <\/a>connected the gene conceptually to a length of DNA on a chromosome.) \u00a0Fisher took the gene to be the atom of evolutionary biology. \u00a0His theory would be about genes.<\/p>\n

In Fisher\u2019s model, there is a single species with a fixed population. \u00a0(In other words, exactly two offspring survive from each mating pair, so that the death rate exactly matches the birth rate, not just in the long run, but exactly in every generation.) Genes circulate freely among different individuals, as they are mixed and swapped and traded during sexual reproduction. \u00a0Different genes do not interact with one another, but each one contributes to making the individual better able to survive and reproduce, or not. \u00a0Those that make a positive contribution to survival and reproduction increase in gene frequency from one generation to the next. \u00a0This just means that there will be more individuals carrying that gene in the next generation than there are in the present generation, because the gene has been successful in enhancing either survival or reproduction. \u00a0This success, in Fisher\u2019s model, is a property of the gene, and he identified the gene\u2019s success in spreading through the population with what Darwin called fitness.<\/p>\n

(Fitness is a property of the gene, not the indivdual animal or the population of animals or the species. \u00a0What might Darwin have thought of this? \u00a0Darwin\u2019s was a very different scientific culture, built on a firm foundation of observation in the natural world, sparing of theoretical claims. \u00a0His “theory” would not be called a theory today, because he never defined terms rigorously, or specified the mechanistic details of natural selection.)<\/p>\n

 <\/p>\n

Fisher successfully argues that his simple model is an accurate reflection of reality<\/strong><\/p>\n

From the beginning, there were questions about whether genes could be considered as free agents, with individual interests of their own. \u00a0A gene only makes sense within a given environment. \u00a0That environment includes other genes, other individuals, and other species. \u00a0Systems in biology are just too interdependent to admit the kind of reductionism that worked for physics, argued Sewall Wright<\/a>, who was Fisher\u2019s intellectual sparring partner in the 1930s and 40s. \u00a0Fisher was a brilliant mind and a commanding presence. \u00a0He won the debates.<\/p>\n

The contentious assumptions on which Fisher\u2019s model was based were<\/p>\n