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ABOUT A MONTH ago I reported on a better-resolution metazoan tree of life. This week the article came out in Nature, and has been followed by a storm of really bad reporting:
Earth’s first animal was the ocean-drifting comb jelly, not the simple sponge, according to a new find that has shocked scientists who didn’t imagine the earliest critter could be so complex.
What’s wrong with this? Basically, the study showed that the line leading to the ctenophores may have diverged before the other metazoan lineages. Stating comb jellies were the “first animal” is going to lead to people thinking that all animals evolved from comb jellies! Some other stories on this article do specify the ctenophore lineage diverged first, which is somewhat less misleading. However, this lineage diverging first does not mean modern ctenophores were there at the time. We might also consider that at that divergence the other lineage produced led eventually to humans, and we certainly were not swimming about in the ocean with the ctenophores waiting for land-living plants and animals to evolve so we could get out and dry off. Modern humans are much different from their early ancestors, and modern ctenophores may be as well.
EVOLUTIONARY TREES will show up fairly frequently here, and are also frequently misunderstood, so I will present a summary of Gregory’s excellent article “Understanding Evolutionary Trees“. I strongly suggest reading it (free full text!) because while I have shown a few of his cladograms he has many more in the paper and goes into much more detail regarding common misunderstandings about evolutionary trees. Some of these misunderstandings are related to the way we tend to think about evolution, some are due to unfamiliarity, and others are learned from obsolete presentations of the process of evolution. Even people who are familiar with evolution may need to pause once in a while and think “Is that a correct interpretation?” when looking at evolutionary trees.
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