The chapter by Douglas Futuyma in 'Evolution' (Losos et al 2013, Princeton) states that natural selection can occur at the species level. Futuyma states that if natural selection occurs at the species level it does not occur at the individual level:

Neither gene selection nor species selection has molded the advantageous characteristics of individual organisms; rather, they have affected properties at the gene level or at the species level.

But how does natural selection occuring at the species level not affect individuals? Surely any selective advantage of a particular species must occur among particular individuals of that species. For example, if Species A is selected because it is browner than Species B, this will be because individuals of Species A are browner than individuals of Species B.

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    $\begingroup$ could you post the word for word quote? $\endgroup$ – rg255 Nov 25 '14 at 19:12
  • $\begingroup$ The quote is word for word. I've also correct a number of mistakes in my question $\endgroup$ – luciano Nov 25 '14 at 19:14
  • $\begingroup$ natural selection works in the genome level. $\endgroup$ – CognisMantis Nov 25 '14 at 20:40

I think you have misunderstood the passage. Here is a larger section (found at google books):

Natural selection can also occur at the level of species, for certain characteristics enhance the rate of origin of new species or diminish the likelihood of species extinction. For instance, the number of species in lineages of herbivorous insects has generally increased faster than in closely related lineages that have other feeding habits. Neither gene selection nor species selection has molded the advantageous characteristics of individual organisms; rather, they have affected properties at the gene level or at the species level. But individual selection, selection among individual organisms within populations, is at the center of evolutionary theory. It is at this level that selection explains most of the adaptive features of organisms.

Going through this part-by-part; the first two sentences state that lineage/species selection can occur, in the sense that species traits can enhance the speciation rate of a lineage or decrease their risk of extinction, relative to other lineages (e.g. in herbivorous insects).

He is then saying that the traits that are the target of this selection are not traits of individuals but traits/properties of the species/lineage.

An example might help to explain the point. For instance, it has been argued that pelagic larvae in sessile ocean species will lead to higher dispersal rates, which means that species can colonize new environments, and this can lead to speciation through adaptive radiation (Jablonski & Hunt, 2006). A larger range will also correspond to lower extinction rates (everything else equal). The trait might also be fixed within a lineage (so there is no variance at the individual level within-species), and if so, this lineage as a whole could have higher speciation rates and lower extinction rates compared to a sister lineage that lacks pelagic larvae.

The individuals within species will naturally have the underlying traits (pelagic larvae), but the traits that are selected at the lineage level (extinction risk & speciation rate) are not properties of individuals but are traits of the lineage/species.

He then ends by continuing with "normal" individual selection, and states that processes at this level is responsible for most adaptive features of organisms. It should also be noted that lineage selection is still considered controversial, and it has been shown that it is inherently much weaker than selection at the individual level. Personally, I think there are some very good examples of how species/lineage selection can function, but to what extent it is an important process for species and organisms is an open empirical question. If you are interested to look further, Jablonski (2008) and Okasha (2007) are two good starting points.

  • $\begingroup$ Nice one - I was just about to head for a google search of the text! $\endgroup$ – rg255 Nov 25 '14 at 19:27
  • $\begingroup$ So if Trait A is selected above Trait B, and if all individuals of a species have Trait A, then this is species-level selection? $\endgroup$ – luciano Nov 25 '14 at 19:29
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    $\begingroup$ @luciano Not quite - its not that simple. You need to think of a lineage in the same way you would about a single species, so that the species within the lineage correspond to individuals within a species. The idea is that all species within lineage A possess trait A and all species within lineage B possess trait B. This can then lead to lineage A increasing faster than lineage B (have higher net speciation rate). That all individuals within all species in lineage A and B possess the same traits can be seen as a byproduct of this. $\endgroup$ – fileunderwater Nov 25 '14 at 19:38
  • $\begingroup$ @luciano The traits do not need to be fixed either. It could just as well be the case that the overall frequency of something is higher in lineage A compared to lineage B, and that this leads to differential properties/traits at the lineage level. $\endgroup$ – fileunderwater Nov 25 '14 at 19:54
  • $\begingroup$ Aha, I think the penny has just dropped. Your comment 2 above this one is what did it. $\endgroup$ – luciano Nov 25 '14 at 20:01

I think there is some misunderstanding there, natural selection does act on an individual and can be determined by its genes (assuming there is genetic variance underlying the variance in trait). Those with more favourable genes will have more favourable phenotypes and thus be more likely to survive/reproduce. However, (genetic) evolution does not occur within an individual, evolution occurs at the population level as the frequencies of existing and new mutations changes over time or space.

Following from your example: Two morphs of a species exist, brown and white (like the classic peppered moth), which is genetically determined, and one has a selective advantage - let's say brown. Thus all individuals of the brown morph are more likely to survive and reproduce. Over time the genes causing the brown phenotype will increase in frequency in the population and frequency of brown (white) moths will have increased (decreased).

I suspect it would be helpful if you included more of the text preceding the statement.

Edit: having seen @fileunderwaters answer, which arrived seconds before I posted mine, I see that I was right, more of the text was useful :)

So going back to the moths, an individual moth would not be able to change it's trait in response to selection.


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