Recently in Development Category

First, you start with a lizard.

Really, I’m not joking. Snakes didn’t just appear out of nowhere, nor was there simply some massive cosmic zot of a mutation in some primordial legged ancestor that turned their progeny into slithery limbless serpents. One of the tougher lessons to get across to people is that evolution is not about abrupt transmutations of one form into another, but the gradual accumulation of many changes at the genetic level which are typically buffered and have minimal effects on the phenotype, only rarely expanding into a lineage with a marked difference in morphology.

What this means in a practical sense is that if you take a distinct form of a modern clade, such as the snakes, and you look at a distinctly different form in a related clade, such as the lizards, what you may find is that the differences are resting atop a common suite of genetic changes; that snakes, for instance, are extremes in a range of genetic possibilities that are defined by novel attributes shared by all squamates (squamates being the lizards and snakes together). Lizards are not snakes, but they will have inherited some of the shared genetic differences that enabled snakes to arise from the squamate last common ancestor.

As part of a year-long Darwin Lecture Series, evo-devo guy Sean Carroll will be giving a webcast talk based around his Making of the Fittest. The talk is on Wednesday, November 4, and you can sign up for the live webcast here.

My first column in the Guardian science blog will be coming out soon, and it’s about a recent discovery that I found very exciting…but that some people may find strange and uninteresting. It’s all about the identification of nodal in snails.

Why should we care? Well, nodal is a rather important — it’s a gene involved in the specification of left/right asymmetry in us chordates. You’re internally asymmetric in some important ways, with, for instance, a heart that is larger on the left than on the right. This is essential for robust physiological function — you’d be dead if you were internally symmetrical. It’s also consistent, with a few rare exceptions, that everyone has a stronger left ventricle than right. The way this is set up is by the activation of the cell signaling gene nodal on one side, the left. Nodal then activates other genes (like Pitx2) farther downstream, that leads to a bias in how development proceeds on the left vs. the right.

In us mammals, the way this asymmetry in gene expression seems to hinge on the way cilia rotate to set up a net leftward flow of extraembryonic fluids. This flow activates sensors on the left rather than the right, that upregulate nodal expression. So nodal is central to differential gene expression on left vs. right sides.

I happened to read PZ’s write-up Local Boy Gets Obnoxious, in which he mentions how he has been interviewed by the Seattle-PI. If I had known PZ was in town, I would have attended the Pacific Science Center talk. Instead I ended up at a Seattle Skeptics “An Evening with PZ MYERS” event. This well attended meetup included a fascinating lecture about the evolution of the eye and introduced me to several aspects of eye evolution with which I had not been familiar.

On Quintessence of Dust Steve Matheson, a biologist at Calvin College, has back to back posts on the role of gene regulation in the development of ‘novel’ structures. The first, How the bat got its wing, describes the work of Chris Cretekos and colleagues on the regulation of Prx1, a gene influencing bone morphogenetic proteins which are involved in limb elongation. The protein coding regions of Prx1 in bats and mice are virtually identical, but in nearby regions thought to contain elements regulating the local expression of Prx1 there are some substantial sequence differences. Replacing the mouse Prx1 forelimb regulatory region with the bat Prx1 regulatory region resulted in mice with significantly elongated forelimbs. Read Matheson’s post for the rest of the story.

In Finches, bah! What about Darwin’s tomatoes? Matheson describes new genetic research on an old friend, the tomato specimens that Darwin brought back from the Galapagos. Didn’t know Darwin brought tomatoes back from the Galapagos? Again, see Matheson’s post for

… an example of a change in a regulatory region of the DNA, the kind of change that evo-devo theorists have predicted to be fairly common in the evolution of new forms.

Michael Le Page at New Scientist discusses Evolution: 24 myths and misconceptions.

Shared misconceptions:

Everything is an adaptation produced by natural selection
Natural selection is the only means of evolution
Natural selection leads to ever-greater complexity
Evolution produces creatures perfectly adapted to their environment
Evolution always promotes the survival of species
It doesn’t matter if people do not understand evolution
“Survival of the fittest” justifies “everyone for themselves”
Evolution is limitlessly creative
Evolution cannot explain traits such as homosexuality
Creationism provides a coherent alternative to evolution

Read on for the much longer list of Creationist myths

Hearts come in a variety of shapes and forms all the way from single chambered hearts to multi-chambered hearts with 2, 3 and even 4 separate chambers. How could evolution have achieved such a feat one may wonder, and indeed creationists have held up this minor mystery as something evolutionary theory could and would never be able to explain.

As is so often the case with such gap arguments, science has not failed to disappoint our creationist friends.

Science Daily gives us a hint of what science has uncovered in an article called Hearts Or Tails? Genetics Of Multi-chambered Heart Evolution

The expanded cardiac field in Ets1/2-activated mutants results in a proportion of animals having a functional, two-chambered heart. “The conversion of a simple heart tube into a complex heart was discovered by chance, but has general implications for the evolutionary origins of animal diversity and complexity”, says Mike Levine, a co-author of the paper.

The evolution of the blowhole in whales, which according to the fossil evidence moved from the tip to the vertex of the head, has caused some concerns amongst our creationist readers who wonder how such a feat could have taken place.

From Milan Klima, Development of the Cetacean Nasal Skull 1999 Springer

The fact that the cetacean nose moved, in the course of evolution, from the tip of the rostrum up to the vertex of the head, is among the most perfect of adaptations to aquatic life. In this and many other special adaptations of their morphology and physiology, cetaceans surpass most primarily aquatic animals even though they themselves have developed from land mammals that breathe with lungs, and have only secondarily conquered the aquatic environment. To a certain extent, cetaceans can be considered to be the most successful group of aquatic animals of all time.

Conclusive paleontological evidence shows the way in which the nasal openings were moved in the course of phylogeny (see Kellogg 1928; Slijper 1962; Gaskin 1976; Oelschlager 1978, 1987, 1990; Moore 1981). That this evolutionary process is repeated in a way during ontogeny became obvious through external observations on embryos and fetuses (Kukenthal 1893). At the earliest embryonic stages the nasal openings are still situated at the rostra tip like those of land mammals; they are gradually shifted more and more towards the vertex of the head at the older stages. At the same time, a long rost rum with narrow jaws develops. Until recently, practically nothing was known about the morphogenetic processes concealed in this metamorphosis, about what cranial structures take part in it, and about the exact way in which the cetacean skull becomes transformed during embryogeny.

The University of California, San Diego (UCSD), the alma mater of Discovery Institute’s spokesperson Casey Luskin, explores why “Evolution Matters”. In cooperation with UCSD-TV, they bring us a fascinating lecture series:

For 2007-08, the Division of Biological Sciences is launching Evolution Matters: The Diversity of Development. In this series of 5 lectures, held over the course of the year, leading cell and developmental scientists will explore the evolution of plants, animals and humans and will discuss how their research into this field holds promise for finding solutions to key health and environmental issues facing us today.

Educational Website: Grey Matters

Educational Website: Science Matters

Atoms to Xrays

Neil Shubin’s latest book on evolutionary theory is by all standards a great success. It ranks around 200 in Amazon books and first in Evolution Science Books. When I checked the book’s availability in our library system there were close to 40 pending holds.

A sales rank of 200 means 225-250 books per week are sold. Compare this to a rank of 24,000 for Behe’s boo “Edge of Evolution” sold at a bargain price of $6.99 down from $28.00 or 111,550 for the regular priced version. Those numbers translate to few copies per month being sold.

Neil Shubin is a professor of organismal biology at the University of Chicago. He, as part of a team of scientists, discovered the now infamous Titaalik transitional fossil which causes so much consternation amongst Intelligent Design Creationists. His book Your Inner Fish introduces its readers to an exciting overview of how our evolutionary history links us back to a common ancestor with fish. Of course, that’s not where our common ancestry ends.

Why do we look the way we do? What does the human hand have in common with the wing of a fly? Are breasts, sweat glands, and scales connected in some way? To better understand the inner workings of our bodies and to trace the origins of many of today’s most common diseases, we have to turn to unexpected sources: worms, flies, and even fish.

In Your Inner Fish, Neil Shubin tells the story of evolution by tracing the organs of the human body back millions of years, long before the first creatures walked the earth. By examining fossils and DNA, Shubin shows us that our hands actually resemble fish fins, our head is organized like that of a long-extinct jawless fish, and major parts of our genome look and function like those of worms and bacteria.

The New York Academy of Sciences provides us with access to a talk by Nobel Laureate Christiane Nüsslein-Volhard on how genes drive development, no need for unspecified ‘Intelligent Designers’, no need for miracles, just hard work by scientists who are committed to discovering the details of how, what, when and so on. Compare this with how ID explains the development of the embryo.

Click on the Flash presentation

I also suggest that interested readers get their hands on her book “Coming to Life: How Genes Drive Development” by Christiane Nüsslein-Volhard or read an excerpt of the book: Chapter IX — Evolution, Body Plans, and Genomes

We are all familiar with the creationist argument about the eye, an argument which Darwin already addressed in his original work. And while creationists are still in much of a denial about eye evolution, science keeps on closing gaps.

In the Australian a second paper addressing eye evolution is discussed.

On Quintessence of Dust, associate professor of Biology Stephen Matheson (yes a Steve Steve), treats us to a fascinating trip through morphospace. He discusses a recent paper by Prusinkiewicz et al.titled Evolution and Development of Inflorescence Architectures, published in Science 8 June 2007:

In this paper, the authors not only show how, despite a multitude of possible forms, severe constraints are placed on biological diversity, but also show how the existence of ‘worm holes’ in fitness space link the various architectures. A beautiful story about scientific inquiry.