# Why does evolution "look" so directed? **URL:** \ **Category:** Factual Questions\ **Created:** [October 15, 2013, 3:22am UTC](https://boards.straightdope.com/t/why-does-evolution-look-so-directed/671280 "2013-10-15T03:22:07Z")\ **Posts on this page:** 20\ **Page:** 3
**Author:** ![MrDibble](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mrdibble/32/114_2.png) [@MrDibble](https://boards.straightdope.com/u/MrDibble)\ **Post date:** [October 16, 2013, 11:35am UTC](https://boards.straightdope.com/t/why-does-evolution-look-so-directed/671280/41 "2013-10-16T11:35:08Z")
> [@Aji\_de\_Gallina](#): > > There is a gigantic random element. Natural selection only acts after the random event. This is a common misconception - that evolution is always mutation+random selection. Needless to say, it’s a gigantic ball of nonsense. Most natural selection acts on pre-existing variation, variability is introduced via recombination and gene flow. And while there’s randomness there, there’s also determinism - sexual selection, for instance. ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [October 16, 2013, 2:42pm UTC](https://boards.straightdope.com/t/why-does-evolution-look-so-directed/671280/42 "2013-10-16T14:42:56Z")
> [@Aji\_de\_Gallina](#): > > Mutations are random and natural selection is non-directed (in the sense that it’s a dumb natural event, no one’s guiding it) and usually very slow (vis a vis a species’ generation time) so that it is unpredictable, that “random” is the right word. “Non-directed” would be an appropriate description. “Random” is not, since selection by definition isn’t. I don’t why you want to insist on using a word that is very misleading. This is like insisting that winning at poker is random just because the deal of cards is. How players choose to play the cards that are dealt has an enormous influence on winning, especially in draw games and over the long haul. The fact that you overstress the importance of randomness is part of your misconceptions about evolution that are shown in the OP. ---
**Author:** ![Smeghead](https://avatars.discourse-cdn.com/v4/letter/s/f1d935/32.png) [@Smeghead](https://boards.straightdope.com/u/Smeghead)\ **Post date:** [October 16, 2013, 3:23pm UTC](https://boards.straightdope.com/t/why-does-evolution-look-so-directed/671280/43 "2013-10-16T15:23:34Z")
> [@Aji\_de\_Gallina](#): > > Mutations are random and natural selection is non-directed (in the sense that it’s a dumb natural event, no one’s guiding it) and usually very slow (vis a vis a species’ generation time) so that it is unpredictable, that “random” is the right word. In addition to what others have said, the idea that natural selection is unpredictable is flat-out wrong. People can, and do, measure precisely the selective pressure on various alleles. Given that information and a few assumptions, you can - and do - predict quite precisely exactly how that allele will spread through the population over time. “Random” is a terrible word to describe evolution. It just isn’t random. It’s not. Sorry. ---
**Author:** ![md2000](https://avatars.discourse-cdn.com/v4/letter/m/73ab20/32.png) [@md2000](https://boards.straightdope.com/u/md2000)\ **Post date:** [October 16, 2013, 3:34pm UTC](https://boards.straightdope.com/t/why-does-evolution-look-so-directed/671280/44 "2013-10-16T15:34:05Z")
No, “random” - in regards to mutations - is perfectly correct. Recombination may do some things, but essentially each minor variation begins as a random mutation. If it is advantageous, or simply neutral, it more likely will survive. Generally these variations are extemely small but incremental. No mammals are going to grow a third set of limbs spontaneously, for example. The complexity of musculature, skeletal support, nerves, brain control areas, etc. required is not likely to end up good and useful in one swell foop. The selection comes about like this - an microorganism that has appendages will have a mutation that creates a double segment - 2 segments, 4 limbs. this becomes 3 segments, 6 limbs, 4 segments 8 limbs, and so on. An organism with rows of appendages probably swims better, more directed, than one with just two. From this form, the limbs specialize - head, tail… you get centipedes with dozens of leg segments; you get lobsters with an array of specialized segment limbs, including the giant from pinchers and the legs. One group - fishes - eventually specialize with 2 sets, the rest are just ribs, spine and tailbones, etc… Evolution builds on the “starter set”. Whatever made it onto land as the beginner organism for amphibians had 4 limbs, so that’s what we have. Reptiles built on that, mammals and birds built more on tthat, etc. If it works, it wins, and that’s the statrer set for the next round of demands on the organism by evolution. So a nerve may have simply gone to the base of the neck and over and up a bit when it was short; then as the neck extended over generations, there was no great penalty for leaving the “design” that way, so evolution did not “get rid” of it. (why would it matter? Speed? Not a problem. Vulnerability? Any trauma that serious to the neck region is likely fatal anyway. The “cost” of growing it like that in overall food and other requirements was not significant. And so on…) ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [October 16, 2013, 3:42pm UTC](https://boards.straightdope.com/t/why-does-evolution-look-so-directed/671280/45 "2013-10-16T15:42:49Z")
> [@md2000](#): > > No, “random” - in regards to mutations - is perfectly correct. No one is disputing that. The problem is that by focusing only just this part of the process is misleading and quite incorrect. It is absolutely wrong to say that “Evolution is random.” ---
**Author:** ![Mijin](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mijin/32/9369_2.png) [@Mijin](https://boards.straightdope.com/u/Mijin)\ **Post date:** [October 16, 2013, 3:53pm UTC](https://boards.straightdope.com/t/why-does-evolution-look-so-directed/671280/46 "2013-10-16T15:53:14Z")
I think the landscape would look similar to any sentient species. You aren’t going to get a sentient species appearing at the slime mould stage, and you also won’t find them sitting around doing nothing for millions of years while another sentient species evolves. They’ll find themselves the smartest thing around, and definitely up there in terms of complexity (if that can be objectively measured), and maybe quite a unique species too – due to the unique selection pressures of living / competing with other sentient individuals. They’d also find themselves pretty much unopposed, with nothing stopping them from either reaching the stars or self-destruction. ---
**Author:** ![md2000](https://avatars.discourse-cdn.com/v4/letter/m/73ab20/32.png) [@md2000](https://boards.straightdope.com/u/md2000)\ **Post date:** [October 16, 2013, 3:56pm UTC](https://boards.straightdope.com/t/why-does-evolution-look-so-directed/671280/47 "2013-10-16T15:56:20Z")
> [@Colibri](#): > > No one is disputing that. The problem is that by focusing only just this part of the process is misleading and quite incorrect. It is absolutely wrong to say that “Evolution is random.” IIRC, this is exactly what Stephen Jay Gould was arguing about the Burgess Shale and one of the earliest explosions of life with massive variations - that survival at that point was not just “survival of the fittest” but when random things like meteor strikes, volcanic eruptions, climate change happen, what survives (especially random catastropes) can as much be pure luck as actual fitness. Did crocdiles and turtles survive the great meteor that destroyed the dinosaurs through survivability, or pure luck? (IMHO a bit of both - these life forms seem to have small, even tiny offspring to start the life cycle; they lived in water habitats better insulated from the initial blast - etc. ) But Gould argues it’s random luck that we are 4-limbed, mirror symettry organisms instea of 5-limbed and not symettrical, for example. ---
**Author:** ![ralph124c](https://avatars.discourse-cdn.com/v4/letter/r/8797f3/32.png) [@ralph124c](https://boards.straightdope.com/u/ralph124c)\ **Post date:** [October 16, 2013, 4:24pm UTC](https://boards.straightdope.com/t/why-does-evolution-look-so-directed/671280/48 "2013-10-16T16:24:03Z")
What about evolutionary “dead ends”-animals like the Giant Panda? It reproduces slowly (the female is only in heat once a year, for a short period) -it can only eat bamboo leaves 9of a certain species) -the males are solitary and don’t stay with the mother and young one -they are marsupials-and the risk of the young dying are very high Obviously, Giant Pandas are never going to take over the world-they are even having trouble surviving in their own niche. Yet this fragile species evolved and thrived-why? ---
**Author:** ![ftg](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ftg/32/2801_2.png) [@ftg](https://boards.straightdope.com/u/ftg)\ **Post date:** [October 16, 2013, 4:38pm UTC](https://boards.straightdope.com/t/why-does-evolution-look-so-directed/671280/49 "2013-10-16T16:38:33Z")
> [@ralph124c](#): > > What about evolutionary “dead ends”-animals like the Giant Panda? > It reproduces slowly (the female is only in heat once a year, for a short period) > -it can only eat bamboo leaves 9of a certain species) > -the males are solitary and don’t stay with the mother and young one > -they are marsupials-and the risk of the young dying are very high > Obviously, Giant Pandas are never going to take over the world-they are even having trouble surviving in their own niche. > Yet this fragile species evolved and thrived-why? Wikipedia is your [friend](http://en.wikipedia.org/wiki/Giant_panda). Not a marsupial. Eats 25 different species of bamboo plus occasional other items. Etc. Note that the habitat of the Giant Panda now is quite different from its habitat before people started clearing the land for agriculture. More varied over a larger area. And in any case, there will always be quite a few species around that are on the verge of extinction. But that doesn’t mean they are dead ends. Humans and several species of large cats have gone thru evolutionary bottlenecks and yet continued on. ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [October 16, 2013, 4:41pm UTC](https://boards.straightdope.com/t/why-does-evolution-look-so-directed/671280/50 "2013-10-16T16:41:31Z")
> [@md2000](#): > > IIRC, this is exactly what Stephen Jay Gould was arguing about the Burgess Shale and one of the earliest explosions of life with massive variations - that survival at that point was not just “survival of the fittest” but when random things like meteor strikes, volcanic eruptions, climate change happen, what survives (especially random catastropes) can as much be pure luck as actual fitness. Did crocdiles and turtles survive the great meteor that destroyed the dinosaurs through survivability, or pure luck? (IMHO a bit of both - these life forms seem to have small, even tiny offspring to start the life cycle; they lived in water habitats better insulated from the initial blast - etc. ) Gould’s interpretation of the Burgess shale is controversial and disputed. In any case that’s rather different than saying that “evolution is random.” Random events certainly influence evolutionary events, but that doesn’t make evolution itself random. Although the asteroid strike that caused the K-T extinction event was by chance, the extinction itself was highly selective, as you mention. > [@](#): > > But Gould argues it’s random luck that we are 4-limbed, mirror symettry organisms instea of 5-limbed and not symettrical, for example. Gould would say that evolution is _contingent_ on chance events, not that evolution itself is random. ---
**Author:** ![Telemark](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/telemark/32/372_2.png) [@Telemark](https://boards.straightdope.com/u/Telemark)\ **Post date:** [October 16, 2013, 4:42pm UTC](https://boards.straightdope.com/t/why-does-evolution-look-so-directed/671280/51 "2013-10-16T16:42:51Z")
> [@ralph124c](#): > > Yet this fragile species evolved and thrived-why? Because it found a niche and survived. There’s no other reason needed. ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [October 16, 2013, 4:45pm UTC](https://boards.straightdope.com/t/why-does-evolution-look-so-directed/671280/52 "2013-10-16T16:45:51Z")
> [@ralph124c](#): > > What about evolutionary “dead ends”-animals like the Giant Panda? > It reproduces slowly (the female is only in heat once a year, for a short period) > -it can only eat bamboo leaves 9of a certain species) > -the males are solitary and don’t stay with the mother and young one > -they are marsupials-and the risk of the young dying are very high > Obviously, Giant Pandas are never going to take over the world-they are even having trouble surviving in their own niche. > Yet this fragile species evolved and thrived-why? Because evolution has no foresight. It can only adapt creatures to present conditions, not to future one. The Panda evolved in response to the availability of a food source that few other animals could use. Their present endangerment is due to changed condition, including habitat loss due to climatic changes and human encroachment. Humans have a very low reproductive rate compared to many other mammals. You could just as well ask why we are so “fragile.” ---
**Author:** ![MrDibble](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mrdibble/32/114_2.png) [@MrDibble](https://boards.straightdope.com/u/MrDibble)\ **Post date:** [October 17, 2013, 9:04am UTC](https://boards.straightdope.com/t/why-does-evolution-look-so-directed/671280/53 "2013-10-17T09:04:52Z")
> [@md2000](#): > > But Gould argues it’s random luck that we are 4-limbed, mirror symettry organisms instea of 5-limbed and not symettrical, for example. I doubt very much that’s what Gould argues (at least, it’s not his argument in _Wonderful Life_) - it’s random luck that, say, insects settled on 3 limb-pairs and decapods on ten, maybe, but the clear advantages of encephalated mirror symmetry over asymmetry are not in the same sphere of “luck” ---
**Author:** ![BigT](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bigt/32/12044_2.png) [@BigT](https://boards.straightdope.com/u/BigT)\ **Post date:** [October 17, 2013, 10:26am UTC](https://boards.straightdope.com/t/why-does-evolution-look-so-directed/671280/54 "2013-10-17T10:26:08Z")
> [@Colibri](#): > > No one is disputing that. The problem is that by focusing only just this part of the process is misleading and quite incorrect. It is absolutely wrong to say that “Evolution is random.” Yes, but the poster in question didn’t just say that evolution was random. He said (bolding mine), “I know evolution is random **and the whole Darwin-natural-selection thingy**.” Random mutations plus natural section is what evolution is. And I see no indication that overplaying the randomness is what caused his confusion. He acknowledged that there would be some natural direction: “I also know that enviromental [sic] pressures load the evolutionary dice in one direction.” So that was not his problem. I think we hit it on the head when we pointed out that the examples we tend to use make evolution look more directed than it actually is. Evolution only looks directed if you look from a very broad view while focusing only a single line. The only thing I think that needs to be added is this: why would evolution go backwards? After you’ve evolved completely away from something, it’s just not there anymore. If you need to go back, why wouldn’t every other new direction be just as likely? For example, why would you expect penguins to redevelop gills, instead of some other way to have enough oxygen while under water? ---
**Author:** ![MrDibble](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mrdibble/32/114_2.png) [@MrDibble](https://boards.straightdope.com/u/MrDibble)\ **Post date:** [October 17, 2013, 10:50am UTC](https://boards.straightdope.com/t/why-does-evolution-look-so-directed/671280/55 "2013-10-17T10:50:47Z")
Loaded dice _are_ non-random. And I _wouldn’t_ expect penguins to develop gills. I wouldn’t be _completely_ surprised if some distant penguin descendant _did_, though, because gills exist in (and occupy a huge part of) the oxygen-extracting-apparatus possibility space, and have separately evolved in multiple lineages. But such a post-penguin’s path through the phenotypic fitness landscape would be _quite_ a long one, and what comes out at the end likely wouldn’t be recognizeable as a bird. Seriously, read _Climbing Mount Improbable_. It deals with this sort of thing quite handily (while demolishing the ignorant Intelligent Design crapfest of “irreducible complexity” AKA “What use is half an eye?”) ---
**Author:** ![Novelty\_Bobble](https://avatars.discourse-cdn.com/v4/letter/n/a3d4f5/32.png) [@Novelty\_Bobble](https://boards.straightdope.com/u/Novelty_Bobble)\ **Post date:** [October 17, 2013, 10:56am UTC](https://boards.straightdope.com/t/why-does-evolution-look-so-directed/671280/56 "2013-10-17T10:56:15Z")
> [@MrDibble](#): > > This is a common misconception - that evolution is always mutation+random selection. Needless to say, it’s a gigantic ball of nonsense. Most natural selection acts on pre-existing variation, variability is introduced via recombination and gene flow. And while there’s randomness there, there’s also determinism - sexual selection, for instance. Dawkins description of the power of sexual selection was a real eye opener for me. I was happy and content with how certain traits aid survival and so are more likely to be passed on but sexual selection potentially adds huge additional impetus to the spread of such traits. As I recall (much simplified and foggy in my memory), males and females may both have genes that give rise to advantageous traits. Over time that may mean there are more of these “enhanced” individuals around to breed with and so on and so on. Fairly straightforward. But what if the opposite sex also has an inherited predisposition to _prefer_ that feature in a mate? (big beak, massive tusks…shapely arse…whatever). Now…within the genes of both sexes, not only do you get increased inheritance of the feature itself, but also a spread in the sexual desire for such a feature, which leads to increased spread of the feature etc. etc. It is a simple extension to the basic evolutionary concept (and obvious once pointed out to you) but the implications are profound. It goes some way to explaining some of the outlandish (and runaway?)sexual displays of some creatures (peacocks?) that tail must surely teeter on the edge of being a disadvantage, but seeing as it works both in terms of satisfying both the environmental and sexual pressures, it persists. ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [October 17, 2013, 11:53am UTC](https://boards.straightdope.com/t/why-does-evolution-look-so-directed/671280/57 "2013-10-17T11:53:08Z")
> [@BigT](#): > > The only thing I think that needs to be added is this: why would evolution go backwards? After you’ve evolved completely away from something, it’s just not there anymore. If you need to go back, why wouldn’t every other new direction be just as likely? > > For example, why would you expect penguins to redevelop gills, instead of some other way to have enough oxygen while under water? An answer to “why would evolution go backwards?” is that much of the genetic code for something an animal used to have is still present. Fewer mutations may be required for something to “turn back on”. Human embryos still have gill slits, for example, after many millions of years on land. Or consider animals who’ve been in caves long enough that they’ve lost their eyesight, but the eyes are still largely there. Maybe the genes to make something are still there, but just switched off. Going “backwards” certainly wouldn’t be guaranteed, but it may be more favorable. ---
**Author:** ![Jonathan\_Chance](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jonathan_chance/32/701_2.png) [@Jonathan\_Chance](https://boards.straightdope.com/u/Jonathan_Chance)\ **Post date:** [October 17, 2013, 12:29pm UTC](https://boards.straightdope.com/t/why-does-evolution-look-so-directed/671280/58 "2013-10-17T12:29:40Z")
> [@DrFidelius](#): > > Hindsight is 20/20. > > When we look back it seems a miracle that we reached “here” despite the plain truth that virtually every other creature who ever lived does not have any surviving descendants. Combined with our story-telling and pattern recognition tendencies it is inevitable that we view biological history as being guided to us as an end product. All the learned discussion of the methods and behavior of evolution are well and good, but DrFidelius has the OP’s answer right here. The quesiton isn’t HOW evolution works and such but rather why it LOOKS directed. That fact stems from the simple reason that we’re looking backwards. We look at humans and through our ancestors all the way back and of COURSE it looks like we were the target development was shooting for. But if we flipped that. Started from the primordial soup (or whatever) it would be considered extremely unlikely that humans would someday develop. There are way to many options moving forward to make that sort of prediction. It’s only in hindsight that it looks obvious. It’s the equivalent of that old metaphor about a single life. Going forward you see all sort of infinite options and pathways you could take. But looking backward from any point it looks like a straight path. That’s because - when looking back - all of the options disappear from most views. ---
**Author:** ![md2000](https://avatars.discourse-cdn.com/v4/letter/m/73ab20/32.png) [@md2000](https://boards.straightdope.com/u/md2000)\ **Post date:** [October 17, 2013, 1:13pm UTC](https://boards.straightdope.com/t/why-does-evolution-look-so-directed/671280/59 "2013-10-17T13:13:27Z")
I’ve never understood that “what use is half an eye” thing. Light-sensitive spots are a useful thing for any creature living in tidal pools and needing to hide under rocks (so predators “feeling around” are less likely to find them.) A collection of light-sensitive spots in a hole will give an indication of direction - where is the shadow coming from? One of evolution’s favourite tricks is duplication - if one of these was useful, a DNA transcription error may give you two or four, etc. For smaller organic structures, this is usually a fairly simple mutation. Once you have a bunch of light-sensitive cells in a pit, having that protrude so it can be aimed without moving the whole body is handy. So is covering the pit with a transparent skin membrane, and so on. The thing with evolution, though, is the selection - once a creature has an advantage, it can more easily wipe out the ones without advantages. When predator and prey both have sight, whose is better is the issue. This sort of pressure is exactly what drives selection. The animal that was happily chomping away on kelp without eyesight is toast very soon. It’s an arms (and eye) race. The same with dinosaurs - we see ever larger herbivores being chased by ever larger predators. As the predators become more dangerous, the prey that evolves more dangerous body armour or even larger body size are best able to fight back. As for going backward… Remember, life evolves to fill an empty niche. We evolved from monkeys in the trees chowing on overripe melons to bipedal marathon runners who could chase down and exhaust our prey. We can’t easily go back to hanging out in the trees, eating fruit, because that job is already taken. Maybe f there were no monkeys or squirrels etc., there would be an opportunity. However, our other adaption is a relatively low birth rate and long reproduction cycle. Long before we started to get smaller and less agile, some rat or possum or lemur would have adapted to fill that niche, literally eating our lunch. So in general, evolution is upward and outward, more specialized. The next wave of creatures likely comes from a smaller, more simple creature. Maybe a few small proto-mammals evolved to take over from the massive dinosaurs. Penguins do basically swim like fishes, but have the added advantage of being able to lay eggs on land well away from the sea-borne predators. As we see with whales, the ability to adapt air-breathing to long deep dives means there is no major benefit to gills in a species that likely only finds its food in the first one or two hundred feet below the ocean. Laying an egg means that in the harsh Antarctica, for example, the female can preload the necessary food supply for gestation, then the couple can tag-team care and feeding of the youngster, rather than the female caring around the full burden all the way. ---
**Author:** ![Alan\_Smithee](https://avatars.discourse-cdn.com/v4/letter/a/2acd7d/32.png) [@Alan\_Smithee](https://boards.straightdope.com/u/Alan_Smithee)\ **Post date:** [October 17, 2013, 5:31pm UTC](https://boards.straightdope.com/t/why-does-evolution-look-so-directed/671280/60 "2013-10-17T17:31:07Z")
**Ludwig Wittgenstein:** Why do people say it is natural to think that the sun revolves around the earth rather than the earth rotating around its own axis? **Elizabeth Anscombe:** Because it looks as though the sun revolves around the earth. **Ludwig Wittgenstein:** Fine, but then what would be like if it looked as if the earth rotates around its own axis? [Previous page](https://boards.straightdope.com/t/why-does-evolution-look-so-directed/671280.md?page=2) [Next page](https://boards.straightdope.com/t/why-does-evolution-look-so-directed/671280.md?page=4)