It seems that there are some taxa that have a greater potential to radiate through adaptations. Off my head, I can think of birds:

Also, there are some fish:

  • Cichlid fish (Lake Victoria in east Africa)
  • Threespine Stickelback





  • Angiosperm plants
  • Dinosaurs
  • Marsupial mammals
  • etc.

So, is there a group of organisms (taxa could be any level: family, gender, species...) that is consistently radiating more than other?

By radiation I take the points that Grant defines here:

These examples have the following in common: (1) they comprise several to many species, (2) the species vary morphologically in conspicuous ways, and relatedly, (3) they occupy a diversity of ecological niches. Most of the species were (4) derived from a single ancestor in their current environment, and (5) most diverged relatively rapidly.

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    $\begingroup$ Threespine Stickelback and Brassica (and other domesticated species) are other examples. $\endgroup$ – Remi.b Oct 20 '17 at 18:47
  • $\begingroup$ Book recommendation: The Ecology of Adaptive Radiation by Schluter $\endgroup$ – Remi.b Oct 20 '17 at 18:48
  • $\begingroup$ Mammals have 2x times larger genomes than birds and lizards, and they radiate faster, which is why there are whales, moles, seals, bats. They have larger genomes partly because mammals have developed anucleated blood cells which are smaller and more flexible than birds, and if birds had very large genomes their blood cells would be less performent. Otherwise there could be burrowing and oceanic birds. $\endgroup$ – com.prehensible Oct 20 '17 at 19:13
  • $\begingroup$ @com.prehens.ible I understand you did not write an answer but just a comment, but really I would need to see a reference stating that 'genome size is correlated with speciation rate and this correlation has to do with blood cells' to believe your comment. $\endgroup$ – Remi.b Oct 20 '17 at 22:55
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    $\begingroup$ Beausoleil, Do you mean phenotype of breeds or species domestication? Remi,esesntially, birds have no choice about accumulating genes. they can't do it well because it clogs their capillaries: (iii) Estimates of speciation interval in mammals correlate positively with genome size. (iv) Genome reductions are inferred at the base of particular species radiations and genome expansions at the base of others. Not a single mammal has a smaller genome than a bird, i.e. a thimble sized vole's is larger than an emu's. $\endgroup$ – com.prehensible Oct 21 '17 at 2:30

The species from your list have some common traits:

  • Fast metabolism of themselves, food and fertilizers
  • sexual reproduction is more complex than crabs and coral
  • complex ecosystems and fast changing ecology
  • lots of ecological competition generally advanced compared to ferns, moss and crabs
  • More Possibility to travel through gene bottlenecks
  • recent in fossil history
  • prevalently small
  • possibility of population explosions
  • generalist and robust flexible habits and traits like tree nests, live birthing, flying, fangs, close inter-animal relations i.e. with bees,

If you study animals that have sedate speciation habits like platipus, they are limited in many of the common traits from that list.

The animal is therefore mostly dependent on it's ecosystem's stability, richness and opportunities, as well as the specie's own physical wealth, opportunism and stability. Those species have very complex and flexible ecology cycles working over them at a high rate. The rate of change of the ecology is also dictated by the other's organisms ability to radiate in record times, so today's species are in an arms race of the fastest rates of change in predator-prey-reproduction traits, with all the tools of the trade, i.e. fast movement, strong protection, freaky efficient cell-type mutations, locomotive, feeding, protective and spacial habits that by themselves can define the base of the most prevalent recent families.

Some species RNA is more susceptible to change and has to be be counterbalanced with different checks, it's to keep up with the arms race of competition in the complex ecology spaces of most of the planet.


You only need two things to radiate rapidly, fast reproduction and opportunity, many of the species mentioned changed rapidly becasue they had access to a wide open environment with little or no competition. They are also small quick reproducing, the faster you breed the faster you can change. A rodent can go through 60 generation in the time an elephant goes through one, that is 60 times as many changes that can occur. Small organisms tend to breed faster so in general small things evolve faster. This is believed to be part of the reason birds survived when other dinosaurs did not.

Another noted factor is generalists tend to survive change better than specialists which means they tend to get to radiate more, they are not necessarily radiating faster they just tend to survive whatever changes opens up niche space for more speciation. Specialists are more likely to go extinct, so generalists end up with more opportunity to radiate.

Now another important facet is preadaptations that can affect oppurtunity. For instance animals with hox genes have a big advantage in creating different body plans over ones without, like nematodes, but note this is only an advantage in this one facet of change, nematodes are arguable one of the most successful lineages ever, they just all have similar body plans. Some argue that having exons/introns helps by more dna to experiment with to get useful mutations, but right now this is just supposition.

Another example of a preadaptation is mammals could not radiate into large sizes until dinosaurs were not around, for instance it was easier for a large dinosaur to expand into large insectivore niche by changing diet than it was for insectivore mammals to evolve large size and all the adaptations to go with that. the dinosaur just had better preadaptations to fill the niche.


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