(posted in Evolution)

I don't know too much about this but there's a short article on the origin and evolution of the head shape in this group of sharks here that may be of interest.

http://www.elasmo-research.org/educatio … origin.htm

(posted in Evolution)

Hi Al,

Divergent selection experiments like this are actually fairly routine in evolutionary biology. Certainly there are selected lines of many organisms including mice, flies and daphnia being set up all the time, and indeed some lines that have been maintained for many (i.e. hundreds) of generations.

Depending on how you want to define and measure "genetic change" (e.g. a measurable change in the average of a trait under strong genetic control, a change in allele frequencies at a particular gene/set of genes), the answer to your last question is not long. You can detect changes over a few generations if you apply some strong selection and if you know where to look. Of course if you work on bacteria you can get a lot of generations in a short space of time which is useful, so these tend to be a favourite fo selection experiments.

I've avoided your second question because it is the hardest to answer! There is another thread on here relating to problems with the species concept that may be worth a look. Basically most evolutionary biologists consider "species" to be a convenient label rather than a hard and fast entity. So the question of how long it would take before the two groups were considered separate species depends entirely on how you define"species." The species concept is really hard enough to apply to natural populations (for which it was developed) so as far as I know, nobody has attempted to apply it to the product of selection experiments. INstead we tend to talk about lines, strains or breeds (e.g. of dog).

(posted in Mammals)

Hi Bruno,

Belugas are indeed found in the St Lawrence, although this system is a big patch of water and I'm not sure how far upstream any of the species found there go (i.e. not sure that any of them enter fresh water). There are of course several species of freshwater dolphin that do live in rivers, but none of them in Canada. For more information about whales and dolphins in the St Lawrence you should have a look at this site.

http://www.whales-online.net/eng/FSC.ht … 1-3-2.html

As for the question relating to the effects of fresh water on a whales body, I may be wrong (if so someone please correct me!) but i think the osmotic challenges may be less than imagine. Moving from freshwater to saltwater (or vice versa) does require particular physiological strategies in fish, but to a large extent this is because of the way in which they transfer gases and salts across the permeable membranes of the gills. For cetaceans this won't be an issue. Perhaps someone will have more info on osmotic issues, but I expect that the problems whales seem to have when they find themselves up rivers are more to do with them being confused, stressed and lost than their salt balance.

I agree with Daniel that "species" is a very human construct. Also to follow up Mike's post, the Biological Species Concept is not only flawed but its also just one of several flawed attempts to come up with a rule for what should/shouldn't be called a species.

Although not necessarily the source of all reliable knowledge, I think the wikipedia entry for "species" is quite good on all this stuff.


I think the key might be in your question here. You may be right that the size is a barrier to mating, but we can't really say what would happen "in the wild" since these are domestic animals.

The species concept is a bit tricky in many ways (e.g., there are quite a few things we call "species" that do naturally interbreed), but is also aimed at classifying natural biodiversity rather than domestic animals. Hypothestically, if all domestic dogs were suddenly released and became wild (or feral I guess) then I'd expect the very big differences between artificially selected breeds to get less with time (i.e. after multiple generations) as all the breeds began to cross. Sure a pure-bred Chihuahua and a great dane may never mate, but maybe both could reproduce with basset hound so the genes would still get mixed up in the wider "mongrel" dog gene pool.

I may be wrong (if so please correct me!) - but I was  under the impression that the "duck feet" mode of transport for fish eggs was a bit of a myth. That is to say it may happen but there's not too much evidence for it.

More generally, its really important to remember that ponds which are now isolated may not always have been and actually would have been connected to each other, and to the sea, in the past. For example, in places like Iceland where glaciers have retreated recently (comparatively.. we're still talking 10000 years), there are many isolated lakes containing fish that would have colonised from the sea (e.g. Arctic charr). As the ice retreated and land rose, the river courses changed and populations would have found themselves in  isolated lakes where they've been ever since.

Also to add to Eric's post. You should never underestimate the impact of humans moving fish. Fishermen have been stocking ponds for as long as they've been catching fish. In the UK there are many non-native species that live in ponds and lakes (e.g. carp, supposedly introduced by the Romans), and in parts of N America fish like the smallmouth bass have been spread far outside their original range because anglers like to catch them.

"Are you saying that using selective breeding... is using evolutionary theory without calling it that?"

Selective breeding certainly is. The theory behind selective breeding is quantitative genetics which is a very important part of evolutionary theory. It is the mathematical framework we use to understand how a trait will change (i.e. evolve) when it is under selection. The theory is identical whether you are trying to understand and predict how milk yield can be increased by artificial selection on dairy cattle, or whether you are trying to understand how a wild plant or animal population will respond to natural selection.

(posted in Mammals)

Hi Francesco,
Generally body size in mammals is considered to be what we call a quantitative trait. This is different from a simple trait (e.g. eye colour) in that what size an animal is depends on many different genes not just one r two. The paper that David has pointed out is a great example of scientists pinning down exactly what some of those genes might be, but there will likely be a lot.

Because there will be many genes involved we can't really say that small size is dominant to big size or vice versa. What we can try and do for quantitative traits is say how much of the variation we see is caused by genes as opposed to environment (e.g. what type of food you have them on. this is something called the "heritability". I'm not an expert on dogs, but if you do some digging I bet breeders have tried estimating heritability for size. The closer the heritability is to 1, the more similar a puppy will be to its parents. However, if you have a high heritability and lots of genes involved, then my expectation from your cross would be that the average size of the puppies was just that  - average! this is because we'd expect them to inherit some genes that make them big (from their mum) and some that make them small (fromn their dad).

Hi Tom,

Just to add to what David said, as well as the massively important medical applications, evolutionary theory is also being used for wildlife and conservation issues. Off the top of my head I can think of many cases where evolutionary biologists are working on improving management of fisheries and animal species that are hunted for food (or trophies). Also there is a lot of evolutionary research into the way in which organisms are (or aren't) adapting to climate change, which is obviously a hot topic and very important when thinking about practical conservation measures.

(posted in Evolution)

Hi Joe,

That's a fantastic question which has been thought about a lot by evolutionary biologists. Although there are some differences of opinion, all the conditions you mention generally happen late in life and are part of what we often call aging or "senescence". The basic point is that is senescense is bad for fitness, why doesn't selection get rid of it?

It's not true to say that they have no bearing on fitness at all, but it is fair to say that because they happen late selection is less effective at minimising their impact - precisely for the reasons you give. This means that for example, genetic mutations causing diseases late in life will they don't get selected out of a population very effectively. Also
some mutations may have a good effect early in life (e.g. make you more fertile) but a bad effect later. Beacuse selection will work more effectively early in life those kind of genetic effects may be kept in the population. There's quite a bit of evidence for these kind of mechanisms now.

So the bottom line is that these conditions aren't selected for, it's that selection against them is not very effective.       


Hi Zelo,

I'm not 100% certain on this, but I don't think the doctors use plastic resins as a material in the surgery. I think that the name really comes from another meaning of the word "plastic", which describes anything that can be shaped or moulded. So it's called "plastic surgery" because they are reshaping your body.