neuroscience - If people with colorblindness lack one type of cone cells, shouldn't they be unable to recognize one particular color?

The 3 types of cone cells in normal humans allow them to view 3 types of colors and any color made from mixing and matching those 3.

So, 2 types of cone cells should only allow to view just 2 types of colors and any colors made from those two.

But that is clearly not the case.

https://en.wikipedia.org/wiki/Color_blindness#Red.E2.80.93green_color_blindness

Protanopes, deuteranopes, and tritanopes are dichromats; that is, they can match any color they see with some mixture of just two primary colors (whereas normally humans are trichromats and require three primary colors).

Also, from personal experience, I'm colorblind and can see and differentiate all 3 red, green, and blue. It's just the hues between red-green and green-blue I can't distinguish much...

How exactly do dichromats see all three colors when they lack one type of cone cell?

neuroscience - Do brain cells shrink during REM sleep or a lucid dream?

For those who have access, here's the full text.

Having read the paper, I can't give you a good answer. This study was performed in mice, not humans, and "sleep" was achieved in a few ways. Mice normally sleep most of the day, so it was easy to get mice sleeping normally. They also induced "sleep" through anesthesia (incidentally, they saw these same results in anesthetized mice, which I think is quite interesting). The state of "sleep" was confirmed mainly through the measurement of brain waves, in particular the delta wave. Delta waves correlate to deep sleep, and that's what they measured. Panels D and G from figure 1 (below) basically confirm just that - the mice were asleep - and that's all we know so far. More exciting research to be done!

human biology - Are (baseline) high blood levels of melatonin associated with either circadian rhythm or mood disorders?

(Exogenous) melatonin is administered at night for treatment of circadian rhythm disorders, but melatonin taken during the day is linked with depression.

I would like to know if high blood levels of (endogenous) melatonin (at a steady state, throughout the day) might be linked with mood or sleep disorders (or have any effect at all), or if the body's response to melatonin adjusts accordingly.

I think the answer to this SE question is related, but I can't find the source using a reverse image search.

evolution - How does natural selection favour large body mass and size (or so it seems)

I was walking through a park this afternoon and observed a few birds having fun flying around and it got me thinking why would natural selection favour birds with flesh at all if it hinders their flight.

We started first with single-cell and micro-organisms flourishing the ponds and then they evolved into massive dinosaurs. It therefore seems, there are some unique reasons for growing to such a large size.

However, I thought it's counter intuitive because the large body slows down locomotion, requires lots of food and energy upkeep, is a big flesh target for predators, makes hiding ineffective.

Although it is obvious that the flesh protects the internal organs, but it seems like a chicken and egg problem because without a massive body, perhaps then there is no need for the internal organs.

On a different perspective, perhaps those animals that evolved without flesh are called plants.

That sums up my naive train of thoughts.

So, any expert can shed some light?

human biology - What could account for an apparent loss of mass at death?

Snopes.com gives a discussion of possible issues with the original experiment. Evaporation or bowel or body movements for instance. I think the biggest complaint about the experiment is that it has not been reproducible and that the original experiment was flawed. MacDougall only took six measurements and he threw two of them out in his original work. The Wikipedia link you give cites a paper where sheep were found to gain weight at least for a time after death. Dogs are found to have no weight change.

MacDougall and his contemporaries were inclined to interpret their results such that animals simply do not have souls, or have different sorts of souls. But if you look at an average of all experiments cited, it could also be said that the average weight loss up on death averages to zero. 3/4 of an ounce of a human being (or a sheep) over the course of something like a death is not an easy measurement. You can't give them a drink of water, you worry that they are breathing too much and losing water. Its not an easy experiment, at least for human beings where you can't control the circumstances of death so well.

In any case this really needs to be measured better. In 90 years it doesn't seem that there's been a real rush to do it.

I just stumbled across this blog post that talks about an effort to measure a change in blood flow to the brain when in intense mental activity popularized in the late 19th century. The investigator Mosso claimed he measured a difference, but the result is disputed today. It could not have been more than a few grams. In any case a description of how difficult this measurement can be.

genetics - Does a large effective population size result in faster decay of linkage disequilibrium (LD)?

It is certainly possible as yes, rapid population growth will reduce LD. From Slatkin, 1994:

In a rapidly growing population, however, there will be little chance of finding significant nonrandom associations even between completely linked loci if the growth has been sufficiently rapid.

Or Nature Reviews, 2002

Przeworski... showed that population growth tends to decrease the extent of LD, especially for longer periods of growth. By contrast, population subdivision tends to increase the extent of LD, especially when a sample contains individuals from several strongly differentiated subpopulations.

See also box 1:

Rapid population growth decreases LD by reducing genetic drift.

bacteriology - Do sulfate reducing bacteria help during the formation of the mineral dolomite in low temperature environments?

Do sulfate reducing bacteria help during the formation of the mineral dolomite in low temperature environments?

Wikipedia says

The actual role of bacteria in the low-temperature formation of
dolomite remains to be demonstrated. The specific mechanism of
dolomitization, involving sulfate-reducing bacteria, has not yet been
demonstrated.

I wonder if someone has any updates on this. The reference given in the Wikipedia article is from 2000, from a source titled suspiciously "Journal of Conference Abstracts". Now it's 2013 and maybe someone else has found out something new.