Is there a limit to macroevolution?

Question: Is there a limit to macroevolution?
- Keywords:
  evolution,
  macroevolution
Asked by bakti to Ed, Katie, Sam, Steve, Vera on 19 Jun 2011.
- Vera Weisbecker answered on 17 Jun 2011:
  
  Depends on what you call a limit. Macroevolution will always happen, so the process itself will never end. But there are some shapes and sizes that can’t possibly be gained by some organisms because of developmental or environmental limits. For example, you won’t get a blue-whale sized land mammal because this beast would crush itself under its own weight. You also won’t get a pig with wings because pig embroys with wings growing simply won’t survive. It is very hard to predict what is possible and what isn’t though. For example, the transition from an ape-like animal to humans happened by a relatively minor genetic tweak that made humans develop very differently – amazing!
- Sam Tazzyman answered on 17 Jun 2011:
  
  “Macroevolution” refers to evolutionary changes such as the splitting of one species into two, or the extinction of species. These are changes on a bigger scale than “microevolution” which is changes within a species. There is no hard and fast line between the two, because macroevolution is simply caused by the adding up of lots of microevolutionary things.
  
  There can be a limit to macroevolution in the sense that the number of species that can coexist in a certain area seems to be limited in some way. This is not something I know a lot about, but it seems as though species have to inhabit some kind of ecological niche, i.e. live in a certain habitat, and eat mainly a certain food type, and so on. Since there are a limited number of niches there may also be a limited number of species. But of course there is feedback, since species themselves can change the environment and so change the number of niches available.
- Ed Morrison answered on 17 Jun 2011:
  
  Another limit I’ve heard is that insects cannot grow much larger than a few inches because of the way they breathe. If they were bigger they wouldn’t get enough oxygen to survive because they don’t have lungs.
- Steven Daly answered on 17 Jun 2011:
  
  Great answers by everyone here!
- Katie Marriott answered on 19 Jun 2011:
  
  I dont know this one. Not my field. I wish I knew more about biological evolution! Chemisty is definitely my strong point!!

Question: Is there a limit to macroevolution?

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