We start with a question that's more complex than it sounds: is modern evolutionary theory "Darwinian"? John Wilkins, at Evolving Thoughts, digresses on the positive and negative meanings that the word "Darwinian" has garnered over the past decades. Unlike religion and doctrines, theories change and evolve as our understanding of phenomena deepens and the technology we use to measure and probe gets better. As such, the theory of evolution has evolved and grown, too, since Darwin set its foundations.
A lot has happened since Darwin published On the Origin of Species. Today's evolutionary theories are drawn from the conjoint effort of many fields: genetics, populations genetics, phylogenetics, epigenetics -- and the list goes on. (And no, phylogenetics do not support intelligent design, despite what some might argue, as reported by David Morrison over at The Genealogical World of Phylogenetic Networks.)
Many contributions to the field come from theoretical models, like the one presented in a recent paper by Roesti et al. (Mol Ecol., 2014, Mar 18). Parallel adaptation is the phenomenon when species from a common ancestor adapt "in parallel" to similar environments. This phenomenon is common in fish: species like the threespine stickleback for example have readapted to river water from marine ancestors. Marius Roesti and colleagues have modeled this parallel adaptation through a "twin-peak and valley model", which he discusses on the Eco-evolutionary dynamics blog.
"Born" in 1942, when CH Waddington coined the term fusing the words epigenesis and genetics, the field of epigenetics is also gradually reshaping the way we think of evolution. Epigenetics makes us rethink heritability, as some changes in gene activity can be passed on to future generations even though they are not encoded in the DNA. In fact, recent studies indicate that some traits can be inherited through gut microbiota.
One of the central ideas in evolutionary theory is fitness. Different phenotypes have different fitness, which is measured in the average number of offspring. Imagine a set of genetic loci, each of which determines a certain phenotype. Any mutation at any one locus changes the phenotype and comes with either a fitness cost or a benefit. One can represent this through a "fitness landscape", a bi-dimensional plane with peaks and valleys: each point on the plane represents a phenotype and the z-axis represents its fitness. With this set-up, the way a phenotype has evolved accumulating a certain number of mutations throughout evolution can be represented as a path in the landscape. Using fitness landscapes, Bjørn Østman and Randy Olson created a video to visualize evolution in action on the Beacon Center blog. You can see more fitness landscapes demonstrating sympatric speciation ("the process through which new species evolve from a single ancestral species while inhabiting the same geographic region") on Randy Olson's blog.
As organisms evolved, some characteristics got lost: "nearly every animal phyla contains at least some species that consistently regenerate all or certain tissues and structures," yet this ability is lost in humans. Tissue regeneration is a fascinating field to study as its mechanisms could help us treating neurodegenerative disorders, spinal cord injuries, and limb amputations. In a blog post on the Beacon, Shawn Luttrell discusses his research at the University of Washington in understanding the morphological and genetic mechanisms of tissue regeneration in Ptychodera flava.
The fact that theories evolve means that definitions need to evolve, too. On his blog, Bjørn Østman discusses how often we disagree on simple definitions, as is the case with "species", for example, which he proposes to substitute with a "criterion" instead of a "definition."
What does Darwinism mean to you? You can join the discussion by filling the survey here.
If you're unsure about the answer, check out the historical quotes Joachim Dagg listed on his blog, Ecology & Evolution Footnotes.
And finally, let's not forget evolution's building blocks: this past Friday, April 25, was DNA day. So, happy DNA day everyone! Until next time!
EDIT: Apparently there was a misunderstanding in the new submission process and I had missed some of the links people submitted. I apologize for that and I'm listing them here below as I have just seen them and haven't been able to read the articles:
- Jason Goldman talks about the Gynosome, a new kind of sexual organ.
- Charles Goodnight gives us a reprise on contextual analysis, a recap on the phenotypic approach and a discussion on kin selection. Charles also writes an interesting essay on indirect effects, individual traits and contextual traits.
- John Hawks talks about Machiavellian intelligence.
- Abbie Smith talks about animated fitness and how it's a "jack in the box" for nerds.
- The discovery of a well preserved 325-million-year-old shark-like fossil from Paleozoic Arkansas provides insight into shark evolution. A post by Janet Fang.
- Henry Gee talks about how variation is maintained in populations and the savannah hypothesis.
- Judge Starling discusses the bimodal distribution.
- Bradly Alicea shares three case studies on Intra- and Inter-generational Physiological Evolution.