Birds and humans look different, sound different and evolved completely different organs for voice production. But now new research published in Nature Communications reveals that humans and birds use the exact same physical mechanism to make their vocal cords move and thus produce sound……
Švec: “To me it was very surprising and fascinating to discover that such different vocal organs make sound in the same way”.
According to Elemans the new discovery not only sheds new light on the sophisticated vocal talents of song birds. The discovery is also interesting and useful because it can be paired with the knowledge about another interesting vocal mechanism shared by some birds and humans: The neural mechanisms underlying vocal learning. Both songbirds and humans are not born with the ability to speak or sing, but must learn their language or song by listening to others, a process called vocal imitation learning or simply vocal learning.
Things slow around here? Looking for some juicy carrots to nibble on? Well, go have a look at Simon Conway Morris’ new website entitled, Map of Life:
This website aims to tell you nearly everything you need (and may ever want) to know about convergent evolution. It allows you to explore the way that similar adaptive solutions have repeatedly evolved from unrelated starting points, as though following a metaphorical ‘map’.
The site archives hundreds of examples of convergence, enough to keep any bunny busy for a long time. I think you’ll like it.
The beauty of the front-loading hypothesis is that it unites the two aspects of evolution that are quite friendly to teleology – deep homology and convergence. As I just explained:
That is, the globin-fold itself is a preadaptation and it is this preadaptative state that restricts possibilities as evolution is much more likely to tap into and exploit this poised, pre-existing state than stumble upon some other possible solution that would be harder to reach. In other words, a significant factor to convergence can be attributed to deep homology, where ancient ancestral states effectively “constrain” where evolution goes.
front-loading expects an intrinsic dimension, where deep homology constrains evolution by functioning as a preadaptation.
This logic is all tied to one of the predictions of front-loading:
Back in Feb 2009, the hypothesis of front-loading evolution allowed me to raise an unconventional perspective on convergence – perhaps many examples of convergence are a consequence of intrinsic constraints rather than purely environmental factors.
Then in June 2009, I added some more support to this prediction in the form of a mitochondrial protein called Tom40. Then I added a ribosomal protein. Then in Jan 2010, there was more support, this time in the form of prestin. A couple of months later, more support came from the VEGF receptors. Again and again, examples of convergence were being explained by factors intrinsic to organisms (preadaptations) and not merely the environment and similar selection pressures.
And let’s not forget that last month, I noted yet another striking example of support:
Okay, I just told ya about front-loading blood, right? Actually, I brought this up over a year ago. Well, let’s now take in the following recent study:
Let’s build on the convergence between vertebrates and cephalopods. This time, let me quote some excerpts from the following article: Squid vascular endothelial growth factor receptor: a shared molecular signature in the convergent evolution of closed circulatory systems by Masa-aki Yoshida, Shuichi Shigeno, Kazuhiko Tsuneki, and Hidetaka Furuyaa (in EVOLUTION & DEVELOPMENT 12:1, 25–33 (2010)).
First, the researchers lay the groundwork for the convergence of these two systems:
Metazoan animals have evolved an incredible diversity of hearts and heart-like structures. The most elaborate case in invertebrates is observed in coleoid cephalopods: they exhibit an elaborate closed circulatory system (Schipp 1987; Budelmann et al. 1997). Their heart possesses a kind of advanced output structure similar to that of the human heart, which differs largely from molluscan typical nonendothelium primitive chambered hearts (see Kling and Schipp 1987; Schipp 1987). Neither morphological nor molecular data give strong support to a close phylogenetic relationship between vertebrates and cephalopods, suggesting that the closed circulatory systems and complicated hearts were formed independently in each lineage, and have converged during their evolution.
Their cardiovascular system is considerably similar to vertebrates in several respects such as high oxygen binding capacity, high concentrations of proteins, and short circulation time (Schipp 1987). Each vessel in the cephalopod is constructed similarly to vertebrate vessels, with an endothelial lining on a basement membrane (Budelmann et al. 1997), although the cephalopod blood vessel lining does not have the cellular junction typical among vertebrate species. Most invertebrates have no endothelium in their vascular walls so the cephalopods are unusual in that they are invertebrates with vertebrate type blood vessels. As the other molluscs have open vascular system, the peculiar blood vessel configuration in the cephalopods is in all probability secondarily developed similarly to the vertebrate among chordates (Ruppert and Carle 1983).
Then, they find something really cool.
Most people are familiar with the human circulatory system, its heart, and its network of blood vessels (you should have learned it in health class!). It represents an example of a closed circulatory system, described as follows:
The blood always remains inside the blood vessels and never comes in direct contact with the cells. The materials enter and exit the blood vessels through the walls. The blood flows in the blood vessels under high pressure such that it reaches all the parts of the body in good time. The blood vessels are branched into fine capillaries which are actually involved in the exchange of materials.
But did you ever hear of an open circulatory system? Here is a nice description:
In higher animals, there are two primary types of circulatory systems — open and closed. Arthropods and mollusks have an open circulatory system. In this type of system, there is neither a true heart or capillaries as are found in humans. Instead of a heart there are blood vessels that act as pumps to force the blood along. Instead of capillaries, blood vessels join directly with open sinuses. “Blood,” actually a combination of blood and interstitial fluid called ‘hemolymph’, is forced from the blood vessels into large sinuses, where it actually baths the internal organs. Other vessels receive blood forced from these sinuses and conduct it back to the pumping vessels. It helps to imagine a bucket with two hoses coming out of it, these hoses connected to a squeeze bulb. As the bulb is squeezed, it forces the water along to the bucket. One hose will be shooting water into the bucket, the other is sucking water out of the bucket. Needless to say, this is a very inefficient system. Insects can get by with this type system because they have numerous openings in their bodies (spiracles) that allow the “blood” to come into contact with air.
And here is a picture to help you better visualize it:
So why bring this up?
Scientists have long cited echolocation in bats and whales as a classic example of convergent evolution. Yet conventional, non-teleological thinking expects convergence to involve different genes, different mutations, and different pathways. As Stephen Rossiter of the University of London notes “it is generally assumed that most of these so-called convergent traits have arisen by different genes or different mutations.”
Yet Rossiter’s research helped to show that the convergent phenotype of echolocation was driven by convergent amino acid changes in the same gene:
“Our study shows that a complex trait—echolocation—has in fact evolved by identical genetic changes in bats and dolphins.”
A hearing gene known as prestin in both bats and dolphins (a toothed whale) has picked up many of the same mutations over time, the studies show.
Let’s return to Lake’s new hypothesis about the origin of double-membrane bacteria:
Here, by analysing the flows of protein families, I present evidence that the double-membrane, Gram-negative prokaryotes were formed as the result of a symbiosis between an ancient actinobacterium and an ancient clostridium.
Since actinobacteria and clostridia might represent cells very similar to the original cells, let’s have a look at them. First, consider actinobacteria.