Monday, October 22, 2012

The network history of the Carnival of Evolution

We recently hosted the 52nd edition of the Carnival of Evolution here at this blog, and since then I have done a bit of digging into the history of the Carnival (or CoE). I am sharing here some of what I found, mostly numbers.

The Carnival of Evolution was founded at the end of August 2008, by Daniel Brown, then of the Biochemical Soul blog. Most blog Carnivals seem to last for only a few issues, but the CoE has continued for more than 50 editions as a monthly summary of "all that is best in evolution blogging". Indeed, it is the only Carnival currently listed as "active" in the Science category, out of the 48 that have existed at one time or another (see this 2009 blog post by Grrl Scientist on the demise of science carnivals).

For longevity, it cannot yet compete with some other biology carnivals, such as I and the Bird, which appeared for 149 fortnightly editions from July 2005 to April 2011, but it has lasted better than most other carnivals — there are 2,964 carnivals listed, but only 136 of these posted an edition during Aug-Oct 2012. For example, the 51st edition of the CoE celebrated precisely 4 years, while the 52nd edition appeared after 1,500 days of continuous blogging. The early editions were intended to be fortnightly, but after a missed hosting early on (at the Life Before Death blog) the plan was changed to roughly monthly intervals, as shown in the first graph.

Frequency histogram of the times
between CoE editions.

The first 18 CoE editions were administered by the afore-mentioned Daniel Brown; but circumstances change for most bloggers, and so he passed the baton to Bjørn Østman, who has carried it since then. There have been 47 different host blogs for the 52 editions — Biochemical Soul, Carnival of Evolution, Greg Laden's Blog, Observations of a Nerd and Quintessence of Dust have all hosted twice. Furthermore, as individuals, Daniel Brown hosted 3 times, and Bjørn Østman, Greg Laden, Steve Matheson, Christie Wilcox and Psi Wavefunction (the Scarlet Pimpernel of evolution blogging) have each hosted twice (not always at the same blog!).

Unfortunately, not all of the 52 Carnivals are still available at the original blogs — number 13 was at a now-deleted blog, the blog hosting number 37 is now access-restricted, and the blogs for numbers 7, 9, and 15 no longer have links to the relevant pages. Fortunately, two of these Carnivals have been archived at the Internet Archive Wayback Machine (#9 and #15), and one is available in a slightly re-formatted form at the blog aggregator Planet Atheism (#37). As for the extinct two, Pleiotropy has a sample list of some of the post topics for #13; but for #7 the only information available is that it was "a short but sweet edition".

This issue raises the related question as to the fate of the 47 blog hosts since their Carnival hosting. As far as I can tell, 1 has been deleted, 1 is now restricted access, 11 have stopped new posts, 5 have continued in another form (eg. another name or address), and the remaining 29 are extant. This shows some remarkable longevity in evolution blogging.

I have looked through the 50 available Carnivals, and I can report as follows. (Note: In the following I took a restricted view of "blog posts" as not including press announcements, of which there have been quite a few.)

There are 283 separate blogs mentioned in the Carnivals, although several of these blogs were moved and/or renamed versions of other blogs, as bloggers tend to move about a fair bit. Of these blogs, 161 (57%) were One Hit Wonders (ie. they were featured only once), as shown in the second graph.

Frequency histogram of the number of
Carnivals in which each blog was cited.

The two blogs with the highest number of Carnival appearances are: Pleiotropy (by Bjørn Østman, naturally!), which was featured in 68% of the Carnivals from number 9 onwards; and NeuroDojo (by Zen Faulkes), which was featured in 69% of the Carnivals from #11 onwards. A special mention should also go to Living the Scientific Life (Grrl Scientist), which was featured in 62% of the Carnivals during numbers 1-29 (she has now drifted into a different form of blogging).

A separate issue is how many actual posts were contributed by each blog (some people blog a lot more than others), which is shown in the third graph.

Frequency histogram of the total number
of posts cited for each blog.

The record of 52 posts is held by The Mermaid's Tale (present from Carnival #30 onwards), which is a multi-author blog (Anne Buchanan, Holly Dunsworth, Ken Weiss), giving them an advantage quantity-wise (and also in diversity of subjects). Mind you, the sole-authored NeuroDojo has 51 posts and Pleiotropy has 49! The record of 10 posts cited in one Carnival is held by Sandwalk (Larry Moran), which was the "specially featured" blog in Carnival #28. Sandwalk also contributed 7 posts to Carnival #50, while The Loom (Carl Zimmer) contributed 6 to #31, and The Mermaid's Tale contributed 6 to #33.

Frequency histogram of the number
of blogs cited in each Carnival.

If we look at these data the other way around, we can contemplate the number of blogs cited per Carnival, in the fourth graph, and the total number of posts cited per Carnival, in the fifth graph.

Frequency histogram of the number
of blog posts cited in each Carnival.

The maximum number of blogs cited in any one Carnival is 44 and the record number of posts is 69, both held by The Dispersal of Darwin (Michael Barton), the host of Carnival #31. (This Carnival also produced the greatest number of One Hit Wonders.) The minimum number is 6 for both criteria, interestingly enough in Carnival #6. The highest average number of posts per blog was 2.1, in Carnival #33 (41 posts cited from 20 blogs).

Fortunately, the number of posts has shown a steady upward curve, as indicated in the sixth graph, although not always at the one-blog-post-per-day rate set in the earliest days. However, over the past 20 Carnivals there has been an average of 1.06 blog posts cited per day of passing time, so we are certainly  holding our own.

The steady growth of the CoE through time.

That's enough about the numbers. What themes have been employed by the CoE host bloggers to present their Carnival? The idea of theme-based presentations was introduced by Daniel Brown in CoE #10, but they appeared only sporadically until CoE #44, since when they have become de rigueur.

The themes we have had are (in order): Darwin's journal, phylogenetic analysis, superstars, a real carnival, Feed Your Head, a football game, a Darwin letter, the Origin of Species, a scientific conference, a conference slide presentation, phylogenetic trees, a newspaper report, an Icelandic saga, mousetraps, a set of teaching modules, Darwin's Restaurant, and phylogenetic networks. Clearly, invention is the name of the game. The most inventive may well be Adrian Thysse's slide presentation in CoE #45; while probably the most outrageous came from Psi Wavefunction in CoE #20, who performed original phylogenetic analyses of the blog posts while claiming no prior knowledge about how to do it!

Finally, and most importantly, we can ask: How has the Carnival of Evolution changed through time? This is precisely what a phylogenetic network is designed to tell us, as shown in the final figure, which is based on a phylogenetic analysis of the data concerning which blogs were cited in which Carnivals.

NeighborNet graph of the similarity relationships between the
Carnivals. The data being summarized are the number of posts
from each blog. So, in the data matrix each row is a Carnival
and each column is a blog, with the data in each cell being the
number of posts. The length of the terminal branches of the
network roughly reflects how many blogs were featured,
whereas the intricate network of inter-connecting lines
indicates the complex patterns as to which blogs were
featured in which Carnivals. Note that #7 and #13 are absent.

As you can see, the analysis shows that there has been a gradient through time. For example, the first 12 Carnivals are at the bottom-right of the diagram and the most recent 12 are at the upper-left of the diagram, with the others arranged in between. (Note that they are not in perfect order.) This means that the blogs being cited have greatly changed through time. For example, none of the blogs featured in the first three Carnivals re-appeared among the most recent four Carnivals.

The biggest change appears to have occurred with Carnival #31. This is indicated by the big gap in the diagram between Carnival #28 and #31 (it is arrowed). Presumably, this had nothing to do with the CoE host (the afore-mentioned Dispersal of Darwin), but has more to do with the time, which was the end of 2010. The world of social media was changing rapidly at that time, and several of the bloggers either stopped blogging or moved house.

It is tempting to interpret the relationships among the blogs in more detail, but that might be tempting fate. I will content myself with pointing out that, in the diagram, the sister to my blog (#52) is Pharyngula (#48), which must be an example of the well-known phylogenetic artifact of long-branch attraction.

Anyway, that's all there is in my network history of the ongoing Carnival of Evolution. Congratulations to all of the people involved in this successful Carnival; but someone else will have to write the centenary history, when it falls due.


  1. Fascinating! Thanks for writing this. I have no doubt CoE will continue and break all the records.

  2. Excellent analysis! Yes, let's keep Carnival of Evolution going. It's good to know that it is one of the most "permanent" blog carnivals around.