Genetic hitchhiking is thought to be an inevitable result of strong positive selection in a population. The basic idea is that if a particular gene is strongly selected for (as opposed to selected against), then the chunk of the genome that carries that gene will become very common in the population.

The third installment of my series at BioLogos is now up.* It discusses the developmental mechanisms that underlie the construction of limbs, and the striking fact that these mechanisms are the same ones used to construct fish fins. Watch for an appearance by Sonic Hedgehog. *Edit July 2020: The series was consolidated into a single article on the BioLogos site. The link now goes to that single article.

The next post will discuss recent evidence for genetic hitchhiking in humans. So, what do we mean when we say that genes can hitchhike? To make sense of this phenomenon, we first need to review chromosomes and sexual reproduction. Most people know that sexual reproduction creates offspring that are genetically distinct from both of the their parents.

Titktaalik roseae.Image fromhttps://tiktaalik.uchicago.edu/index.html The second post in my series on limb evolution is now up at the BioLogos site. This installment reviews the fossil evidence on fin-to-limb evolution, introducing the famous Tiktaalik . Next up: evidence from developmental biology. The first post at BioLogos outlined limb structure and some historical background.

Not surprisingly, Hamlet weighed in on the nature vs. nurture question, at least once. It is certainly true that "the stamp of one defect" can wreak havoc on the scale that Hamlet describes, and whether the result is a debilitating physical limitation or damage to "the pales and forts of reason," the outcome is tragic by any measure.

Last month, I started a series on the topic of limb evolution, here at Quintessence of Dust. That series has been transformed (through a series of intermediates) into a series of posts* at the BioLogos site. The first installment is now up, and it provides an expanded introduction to the topic and a little historical context.

In the cartoon version of evolution that is often employed by critics of the theory, a new protein (B) can arise from an ancestral version (A) by stepwise evolution only if each of the intermediates between A and B are functional in some way (or at least not harmful). This sounds reasonable enough, and it's a good starting point for basic evolutionary reasoning.

The discovery of deep homology was a milestone in the history of evolutionary thought. Anatomical structures in distantly related organisms, structures with only the barest of functional similarities, were found to be constructed under the influence of remarkably similar genetic pathways. The original and classic example from 1989 involves genes controlling pattern in both insects and mammals – the famous Hox genes.

"The Selfish Gene." "Selfish DNA." Oh, how such phrases can get people bent out of shape.  Stephen Jay Gould hated such talk (see a little book called The Panda's Thumb ), and Richard Dawkins devoted more time to answering critics of his use of the term 'selfish' than should have been necessary.

It is of course a cliche to state that eukaryotic cells (i.e., cells that are not bacteria) are complex. In the case of an animal, tens of thousands of proteins engage in fantastically elaborate interactions that somehow coax a single cell into generating a unique and magnificent organism.