Book Club: Chapter 2: The Everyday Math of Evolution

In this chapter, Carroll introduces the role of probability into evolutionary theory, although, he accidentally displays how probability is often misused. It may be true that the chance of being eaten by a shark is 1 in 300 million – if 300 million people actually exposed themselves to shark attack each year. In reality, it is only those who enter shark populated water that are actually at risk – therefore, the real risk to those putting themselves in harm’s way is actually higher. This may seem to be a minor point, but it serves as a reminder of the misuse of probabilities by creationists. They often build straw man arguments to claim that evolution is mathematically impossible – usually involving inane positions that pretend 300 amino acids randomly coming together to form a functional protein.

Carroll does however convincingly demonstrate using models and real studies that evolution can produce new traits in a population in a relatively short time. He cites the change in the peppered moth population from light coloured to dark coloured in response to environmental pollution darkening the trees. This has probably happened on at least 4 separate occasions, as there are 4 known different mutations that cause the dark phenotype. He also gives a more recent example of pigeon populations developing a white rump. This gives them an advantage when it comes to avoiding attack by falcons; perhaps by momentarily confusing the falcon as the pigeon rolls to avoid the attack.

The rate of change in the population is proportional to the selection coefficient, and his example of mouse populations becoming all black in less than 2000 years is discussed here. He makes the point that not all individuals survive and that this is determined by the advantage/disadvantage a particular gene confers on its owner. There is also some discussion about whether natural selection acts on small or large differences between organisms. He comes down on the side of small changes. However, I would argue that it acts on both, as small changes in genes can actually cause a big difference in a characteristic. An example would be the genes controlling the sizes of tomato plants.

He introduces the idea of plasticity in species at the start of the chapter (and its role in Darwin forming his ideas of evolution) and ends with listing some of the possible types of mutation that occur – insertions, deletions, inversions, duplications, cut and paste, single nucleotide substitutions etc and will discuss some of these later in relation to evolving new functions. He also attacks the notion that all mutations are harmful. Some are actually beneficial (see above and here) and some a neutral and have no effect on function. This latter type of mutation can be used to study the effect of selective pressures on the rates of gene changes – by providing a reference point to the effect of random cumulative mutation.

Spiders On Drugs

The fact that drugs can affect personality and cognitive processes is good evidence against the idea that the mind is something other than physical. Anyway, here is an amusing video

I'll get the next chapter of the book club up by Sunday - the dog ate my computer.

Icy Ben Vane

A friend took a couple of short videos on Ben Vane yesterday. They are linked here and here. As winter conditions go, these are quite mild. See here for a more serious version of winter conditions.

Book Club - Chapter 1

In the preface and the first chapter, Carroll spells out his intentions for the book. He makes the point that DNA evidence is used in courts to convict criminals. This technology works because of subtle differences in the sequences of DNA amongst different individuals. These same differences when read as sequences can reveal relatedness amongst individuals too. The further back in time we go, the less we share with parents, grand parents and great grandparents. This time line goes all the way back to the hypothetical Last Universal Common Ancestor (LUCA) of all species. The result is that the more related that we are to a species, the more similarity we have in our DNA sequences.

Carroll points out the main points of Darwinian evolution; that are descent with modification and the selection of the best adapted for the environment. This occurs through random mutations and selection of these mutations over large periods of time. Organisms are shaped by their environments – both physical and biological. They can therefore be seen as solutions to problems. To illustrate this principle of physiological ecology, the author uses the examples of ice fish. Their ancestors had to deal with the problem of a cooling ocean. To adapt to this, they evolved some antifreeze proteins (discussed in more detail in this post). These came about through the random mutation of part of the trypsinogen gene. This provides evidence for the capacity of organisms to create new genes from old ones (discussed here and here). That is descent with modification and is an essential feature of evolution that religious fundies often misrepresent. They claim that complex structures like eyes are supposed to have evolved in a generation or two. This however is not how evolution works. It works through many small cumulative (undirected) steps that use genes that are already there. A proper model for eye evolution can be found here. Around the same time, their genes for tubulin became modified in such a way that allowed them to tolerate lower temperatures. This allows their cells to retain their normal architecture and function at lower temperatures than would otherwise be tolerable.
One problem, which is not fully discussed is that the presence of antifreeze proteins increases the viscosity of the blood. This would strain the cardiovascular system. However, cold water carries more dissolved oxygen than warm water. This meant that the fish could get large quantities of oxygen from solution. This allowed the fish to decrease the number of circulating red blood cells (which carry oxygen) allowing them to decrease the viscosity of their blood. A reduced demand for red blood cells meant that there was no need for haemoglobin – the oxygen carrying component of red cells. This lead to the loss of these genes (see here). Other adaptations include a loss of scales and an increase in capillary number in the skin – this allowed the skin to take up oxygen as well as the gills. Finally, some species also lost their genes for the oxygen storing myoglobin. This is an other principle of evolution – you lose what you don’t need through random mutation (see here). The non-functional remnants of these genes can still be found in these fish. This tells a nice story of how genomes can change in response to environmental conditions

Carroll then goes on to outline his plans for the book, and finishes with a ca bit on why evolution matters. He concentrates on food production, but I felt he could have spent a bit of time on the evolution of antibiotic resistance, the role of animal models in medicine and the fact that it is important in its own right regarding the origins of species.

Happy Darwin day.

Maiacetus Inuus: A New Transitional fossil Of The Whale Lineage

Whale evolution is something that I have blogged on before. This paper describes the discovery of yet another transitional fossil between artiodactyls and whales. The new species is called Maiacetus inuus, which means mother whale of inuus ( Inuus being the Roman god of fertility). It is so called, because one specimen was pregnant (the foetus is the blue shaded object below). What is interesting is that it is in a head down position; modern whales give birth tail first. This suggests that birth still took place on land. Not surprisingly, it is found in the right part of the world to be an intermediate form (Pakistan) and its morphology dates to the correct era too; 47.5 million years old. This makes it older than the more whale like Basilosaurids, and younger than the more primitive Ambulocetus, Indohyus and Pakicetids.

Pesky Pistol Shrimps

I have a pistol shrimp in my reef aquarium. They are supposed to be safe with other inhabitants, but I found one of the cleaner shrimp dead and a couple of sexy shrimp have gone missing (I presume they are so called because they "dance" while they walk). I did a bit of research and apparently not all species are safe and found the video below of one stunning a cleaner shrimp. This is quite fascinating - when the little bastards are not eating their tank mates.

They have a specialised claw that sends out a violent jet of water and a sound wave that whacks its prey. This video goes into the mechanics of the sound production.

This hunting/defense adaptation is also a problem for deluded Young Earth Creationists who believe god made all animals vegetarian. How did they get this adaptation without evolution? No doubt they will pull some bollocks out their collective chuffs like god intended them to eat coconuts and the snap breaks the shell.

A final interesting thing about these shrimp is that they often enter a symbiotic relationship with certain species of goby. The goby provides the lookout and bits of food and the shrimp provides a protective burrow and firepower. This an example of being co-operative yet selfish. It is such a creationist lie that natural selection means kill everything.

Anyway, I wonder who would win in a square go between a pistol shrimp and a mantis shrimp (which can deliver a blow equivalent to being hit by a .22 bullet). Following Bruce Lee's advice of using your longest weapon, I would bet on the pistol shrimp. All we need now is Harry hill to proclaim Fiiiiight!