Sex Ratio Redux...

The idea of sex ratio being an ESS is broken down in an easy to follow manner in W.D. Hamilton's work published in his 1967 paper: "Extraordinary Sex Ratios"...follow this link http://www.sciencemag.org/cgi/content/citation/156/3774/477

This is based on the assumption the condition that males and females cost equal amounts to produce:
1. Suppose male births are less common than female.
2. A newborn male then has better mating prospects than a newborn female, and therefore
can expect to have more offspring.
3. Therefore parents genetically disposed to produce males tend to have more than average
numbers of grandchildren born to them.
4. Therefore the genes for male-producing tendencies spread, and male births become
more common.

As the 1:1 sex ratio is approached, the advantage associated with producing males dies away.
The same reasoning holds if females are substituted for males through-out. Therefore 1:1 is the equilibrium ratio.

Fisher seems to have been looking at this from a parental expenditure standpoint.

Fisher's principle is an ESS because once it has been established in a population, it benefits those that "play by that rule" and punishes those who deviate from the ESS.

The sex chromosome assymetry is interesting, due to the fact that xx are homogametic and xy are heterogametic. Y should benefit, because XX never passes along the y chromosome, but x should benefit because the homogametic sex passing it along (but with only half the efficiency). The mitochondria (as well as some other non-nuclear genetics) can bias because they are only carried on through the cytoplasm of the egg. Other non-nuclear items causing bias are bacteria that may be "male-killers".

September 23 Blog Post

As a public school science teacher, I am always thinking of ways to teach the evolution of organisms without causing a disturbance...yet, I'm always thinking about the evolution of things. What amazes me about evolution is nothing is done frivolously. Things that aren't needed disappear. If only business worked in the same way...

Anyhow...thinking of the "spark" of life and how the molecules needed came about...I buy into the "negative mould" idea. Having to break down protein synthesis for freshman bio students I have come to appreciate the simplicity AND complexity of the process. In a "primordial soup" of inorganic chemicals (subjected to incredible amounts of lightning), I don't find it at all a stretch that self-replicating chains of certain molecules (that attract their opposite) would start to form.

It also doesn't surprise me that the more stable of the molecules would continue to exist, whereas the less stable wouldn't. Eventually those that created larger replicating groups became more and more complex, but the end goal was still to make more.

As energy was required for these bags 0f chemical reactions to continue on, small changes that led to the production of food from light or chemicals (photoautotrophs and chemoautotrophs) would have led to an increased stability. Items that required energy, but couldn't use light/chem to produce food brought in energy from the outside (heterotrophs). It has always been my understanding/belief that chloroplast and mitochondria may have begun as free-living, self replicating items (as indicated by the double membrane they posses and the mitochondrial DNA) that were integrated into anther cell and incorporated into the processes of the cell itself.

Selectional pressure seems likely to have played a role in creating similar acting/looking/behaving items based on convergent/divergent evolution. Reacting to similar environmental conditions would make many of these items similar to each other, even though they had different paths to get to a point (convergent)...and on the flip side, items that started to fill niches would break away from a group to avoid competition.

I think that Mayhew and Dawkins are pushing in the same direction on this. Mayhew looks at it from the standpoint of how organisms evolved and how they fit into their environment, and Dawkins does as well...but they differ in audience. I feel like Mayhew is working on my previous science knowledge and expanding it, but Dawkins is almost trying to CONVINCE me of something that he knows and is making a persuasive argument (look at the language). Dawkins is explaining how the engine works, but Mayhew is describing how the car fits into or society.

-Black 9/21/09 10:15 a.m.

Tuesday 9/15 Reading Question

I would counter Darwin's argument by using his example of the various pigeon breeds being selectively bred to establish certain traits not shown in the Rock Pigeon. Why he could see this with one species, but not another is interesting.

Darwin's argument for the domestication of dogs and his rationale for the domestication of pigeons is different, but in my opinion shouldn't be. He argues that such different varieties of pigeon are surely to come from the rock pigeon, but argues that dogs couldn't have come from a single common ancestor. My understanding of species tells me that a species must be able to breed and produce viable offspring. With domesticated dogs (even with the mechanical issues between large and small dogs) artificial insemination would produce a viable offspring. The other problem I have with Darwin's assertion that dogs were bred from a few aboriginal species is there are no aboriginal species running around with similar traits as the greyhound or bull-dog. Where did they go? Of course genetic testing and genome studies are methods to confirm these ideas.

Crossing dogs that have traits that are desired to a breeder would result in offspring that may show these traits...but it would take many generations to isolate and propagate these traits. The Labradoodle is a fine example because of the gentle nature of the Lab (c'mon...ever seen a mean lab?) and the desired trait of an allergy free coat from the Poodle...and it didn't take long for the breeders to get the desired set of traits. According to a Labradoodle website (http://labradoodle-dogs.net/labradoodle-history/) the breed wasn't stared until 1988.

Dawkins looks at what Darwin couldn't. His idea of a "stable" group is one that can carry on based on stability. The domesticated dog has been around long enough for humans to name them. The genetics behind stability is the basis of speciation based on artificially selected traits (by humans) or by the environment. Evolution itself doesn't have an end goal, but artificial selection does. Anyone who has lived with a bull-dog knows that the respiratory problems associated with that breed (in the wild) wouldn't be "stable". The environment selects for stable groups that survive what "she" throws at them, not what traits are desired by "her". Darwin was on the right track, I just don't know why he got the pigeon thing right, and the dog thing wrong.

Ecology could have played a role in the domestication of the dog because of the interaction between a few species. There are very complex social interactions between wolves in a pack environment. The less aggressive wolf may not have survived in a pack situation and may have even been driven from the pack to fend for itself. The proliferation of hunter-gatherer human clans may have been a substitute for the more "tame" wolf, and followed or even been "adopted" by a clan. Both organisms may have benefited from the company of the other (food for the wolf... an "early warning system" for the humans...companionship for both)...but artificial selection would have been the next step. As we discussed in class, the humans would need to remove the more aggressive offspring and kept only those pups that demonstrated the desired trait. Inbreeding and other genetic variation may have played a role, as well as finding other docile individuals until the dog and wolf failed to reproduce based on behavior, not only genetics.

Much like Darwin working on an idea at the same time as Wallace, I'm sure that clans all over were also beginning the process of domesticating dogs, as well as other animals.