{"id":3375,"date":"2022-11-19T06:39:45","date_gmt":"2022-11-19T06:39:45","guid":{"rendered":"https:\/\/alife.org\/?post_type=encyclopedia&#038;p=3375"},"modified":"2022-11-19T06:49:57","modified_gmt":"2022-11-19T06:49:57","slug":"fitness-landscape","status":"publish","type":"encyclopedia","link":"https:\/\/alife.org\/encyclopedia\/digital-evolution\/fitness-landscape\/","title":{"rendered":"Fitness Landscape"},"content":{"rendered":"\n<p>A <a href=\"https:\/\/alife.org\/encyclopedia\/digital-evolution\/fitness\/\" target=\"_blank\" title=\"Fitness is a quantification of an individual's evolutionary success. In biology, an individual's fitness is generally measured as the number of offspring that individual has. Many artificial life platforms operate in the same manner, encoding rules that determine when individuals reproduce and then allowing evolution to take its course (some individuals will reproduce more, consequently&hellip;\" class=\"encyclopedia\">fitness<\/a> landscape is a mapping from a combination of trait values to a fitness. They are generally visualized so as to make it clear which trait values are closer to each other (i.e. easier to mutate between). Traditionally, for the purposes of easy visualization, they are drawn in three dimensions (x, y, and z axes). The x and y axes each represent a trait (i.e. a property that an individual might have). The value on the z axis represents the fitness of an individual possessing a given combination of trait value. This approach creates an intuitive topographical visualization, where we expect to see populations climb &ldquo;hills&rdquo; in fitness space over time. Most real world fitness landscapes, however, have *many* more dimensions.<\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img decoding=\"async\" src=\"https:\/\/upload.wikimedia.org\/wikipedia\/commons\/f\/fe\/Visualization_of_a_population_evolving_in_a_static_fitness_landscape.gif\" alt=\"A gif of a population evolving on a static fitness landscape\"><\/figure>\n\n\n\n<p>The following two videos may be helpful for a more detailed introduction:<\/p>\n\n\n\n<figure class=\"wp-block-embed is-type-video is-provider-youtube wp-block-embed-youtube wp-embed-aspect-16-9 wp-has-aspect-ratio\"><div class=\"wp-block-embed__wrapper\">\n<p class=\"responsive-video-wrap clr\"><iframe loading=\"lazy\" title=\"Fitness Landscape\" width=\"1200\" height=\"675\" src=\"https:\/\/www.youtube.com\/embed\/JPTIZbGGYmk?feature=oembed\" frameborder=\"0\" allow=\"accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture\" allowfullscreen><\/iframe><\/p>\n<\/div><\/figure>\n\n\n\n<figure class=\"wp-block-embed is-type-video is-provider-youtube wp-block-embed-youtube wp-embed-aspect-16-9 wp-has-aspect-ratio\"><div class=\"wp-block-embed__wrapper\">\n<p class=\"responsive-video-wrap clr\"><iframe loading=\"lazy\" title=\"Sewell Wright's Fitness Landscape Metaphor Explained\" width=\"1200\" height=\"675\" src=\"https:\/\/www.youtube.com\/embed\/_XvHaQMJkzQ?feature=oembed\" frameborder=\"0\" allow=\"accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture\" allowfullscreen><\/iframe><\/p>\n<\/div><\/figure>\n\n\n\n<h1 class=\"wp-block-heading\">Approaches to visualizing fitness landscapes<\/h1>\n\n\n\n<p>While the topological visualization discussed above is effective for landscapes with one or two non-fitness dimensions, it presents a challenge for higher-dimensional landscapes (such as most real-world fitness landscapes). One common approach is to use a graph instead. Each genotype is represented as a node, and mutational-adjacency of genotypes is represented with edges between nodes. While this representation is powerful, in many cases the graph can become a tangled mess that is hard to gain intuition from. Making intelligent choices about how to position nodes can help with this problem, as can having a relatively small or intuitively structured landscape. <\/p>\n\n\n\n<p>For example, it is relatively common in evolutionary medicine to represent fitness landscapes for the presence\/absence of 4 genes (leading to 16 possible genotypes) in the &ldquo;tesseract&rdquo; layout below <span class=\"zp-InText-zp-ID--4204406-Q5JJUTNW-_-4204406-6LGFLFZM--wp3375 zp-InText-Citation loading\" rel=\"{ 'pages': 'np', 'items': '{4204406:Q5JJUTNW},{4204406:6LGFLFZM}', 'format': '(%a%, %d%, %p%)', 'brackets': '', 'etal': '', 'separator': '', 'and': '' }\"><\/span>:<\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"868\" height=\"444\" src=\"https:\/\/alife.org\/wp-content\/uploads\/2022\/11\/GraphFitnessLandscape.png\" alt=\"An example graph-based fitness landscape, representing a scenario where there are four traits of interest, each of which can be present or absent. Mutations can add or remove a single trait at a single time.\" class=\"wp-image-3573\" srcset=\"https:\/\/alife.org\/wp-content\/uploads\/2022\/11\/GraphFitnessLandscape.png 868w, https:\/\/alife.org\/wp-content\/uploads\/2022\/11\/GraphFitnessLandscape-300x153.png 300w, https:\/\/alife.org\/wp-content\/uploads\/2022\/11\/GraphFitnessLandscape-768x393.png 768w\" sizes=\"(max-width: 868px) 100vw, 868px\"><figcaption class=\"wp-element-caption\">An example graph-based fitness landscape, representing a scenario where there are four traits of interest, each of which can be present or absent. Mutations can add or remove a single trait at a single time.<\/figcaption><\/figure>\n\n\n\n<h1 class=\"wp-block-heading\">Critiques of fitness landscapes<\/h1>\n\n\n\n<p>There is widespread concern that intuitions based on the low-dimensional representations of fitness landscapes that must necessarily be used in most visualizations may not translate accurately to realistically sized landscapes. As dimensions are added to a space, properties of that space such as connectivity may change in a systematic way. Thus, some have speculated that concepts such as &ldquo;valley crossing&rdquo; (i.e. the evolutionary difficulty of reaching one local optimum from a different one) may not be relevant in most real-world fitness landscapes.<\/p>\n\n\n\n<h1 class=\"wp-block-heading\">Further reading<\/h1>\n\n\n\n<ul>\n<li><a href=\"https:\/\/www3.beacon-center.org\/blog\/2014\/04\/07\/beacon-researchers-at-work-holey-fitness-landscapes\/\">BEACON Blog post on Holey Fitness Landscapes<\/a><\/li>\n\n\n\n<li><a href=\"https:\/\/www3.beacon-center.org\/blog\/2012\/10\/08\/evolution-101-fitness-landscapes\/\">Evolution 101: Fitness Landscapes<\/a><\/li>\n\n\n\n<li><a href=\"https:\/\/www3.beacon-center.org\/blog\/2015\/05\/13\/tortoises-hares-and-topography-how-fitness-landscape-structure-affects-speed-adaptation\/\">Tortoises, hares, and topography: how fitness landscape structure affects the speed of adaptation<\/a><\/li>\n<\/ul>\n","protected":false},"excerpt":{"rendered":"<p>A fitness landscape is a mapping from a combination of trait values to a fitness. They are generally visualized so as to make it clear which trait values are closer to each other (i.e. easier to mutate between). Traditionally, for the purposes of easy visualization, they are drawn in three dimensions (x, y, and z [&hellip;]<\/p>\n","protected":false},"author":2,"featured_media":3576,"template":"","encyclopedia-category":[93],"encyclopedia-tag":[122,114],"coauthors":[89],"_links":{"self":[{"href":"https:\/\/alife.org\/wp-json\/wp\/v2\/encyclopedia\/3375"}],"collection":[{"href":"https:\/\/alife.org\/wp-json\/wp\/v2\/encyclopedia"}],"about":[{"href":"https:\/\/alife.org\/wp-json\/wp\/v2\/types\/encyclopedia"}],"author":[{"embeddable":true,"href":"https:\/\/alife.org\/wp-json\/wp\/v2\/users\/2"}],"version-history":[{"count":2,"href":"https:\/\/alife.org\/wp-json\/wp\/v2\/encyclopedia\/3375\/revisions"}],"predecessor-version":[{"id":3574,"href":"https:\/\/alife.org\/wp-json\/wp\/v2\/encyclopedia\/3375\/revisions\/3574"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/alife.org\/wp-json\/wp\/v2\/media\/3576"}],"wp:attachment":[{"href":"https:\/\/alife.org\/wp-json\/wp\/v2\/media?parent=3375"}],"wp:term":[{"taxonomy":"encyclopedia-category","embeddable":true,"href":"https:\/\/alife.org\/wp-json\/wp\/v2\/encyclopedia-category?post=3375"},{"taxonomy":"encyclopedia-tag","embeddable":true,"href":"https:\/\/alife.org\/wp-json\/wp\/v2\/encyclopedia-tag?post=3375"},{"taxonomy":"author","embeddable":true,"href":"https:\/\/alife.org\/wp-json\/wp\/v2\/coauthors?post=3375"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}