So, on ScienceDaily there is a story (adapted from a press release by the University of Bath) about an interesting study in PNAS regarding patterns of macroevolution in crustaceans. In particular, it seems that there is often an increase in morphological complexity over time in different lineages within this group, which makes sense because complexity in this case relates to specialization of limbs and so on. (Lineages necessarily begin simple, with repeated segments that are the same, then some limbs evolve to become specialized for feeding, walking, swimming, and so on — it’s probably a driven trend in that it is adaptive to have specialized features, but one also can really only increase in complexity when the beginning is around some minimum level of simplicity, as one of the authors notes in the story).
Here is the abstract:
The prospect of finding macroevolutionary trends and rules in the history of life is tremendously appealing, but very few pervasive trends have been found. Here, we demonstrate a parallel increase in the morphological complexity of most of the deep lineages within a major clade. We focus on the Crustacea, measuring the morphological differentiation of limbs. First, we show a clear trend of increasing complexity among 66 free-living, ordinal-level taxa from the Phanerozoic fossil record. We next demonstrate that this trend is pervasive, occurring in 10 or 11 of 12 matched-pair comparisons (across five morphological diversity indices) between extinct Paleozoic and related Recent taxa. This clearly differentiates the pattern from the effects of lineage sorting. Furthermore, newly appearing taxa tend to have had more types of limbs and a higher degree of limb differentiation than the contemporaneous average, whereas those going extinct showed higher-than-average limb redundancy. Patterns of contemporary species diversity partially reflect the paleontological trend. These results provide a rare demonstration of a large-scale and probably driven trend occurring across multiple independent lineages and influencing both the form and number of species through deep time and in the present day.
The news release itself is interesting, and includes an excellent quote from the study’s lead author Sarah Adamowicz:
Our results apply to a group of animals with bodies made of repeated units. We must not forget that bacteria – very simple organisms – are among the most successful living things. Therefore, the trend towards complexity is compelling but does not describe the history of all life.
And yet, the headline of the piece is…
First ‘Rule’ Of Evolution Suggests That Life Is Destined To Become More Complex
Do the people who determine headlines not even read the stories?