"Sex results in a more youthful appearance. According to a study by Dr David Weeks, a clinical neuropsychologist at the Royal Edinburgh Hospital in Scotland and co-author of Superyoung (1999), men and women who reported having sex an average of four times per week looked approximately 10 years younger than they really were."???????

How about if you look 10 years younger than you really are (and that is already very subjective) you get lucky more often?

"Sex results in a more youthful appearance. According to a study by Dr David Weeks, a clinical neuropsychologist at the Royal Edinburgh Hospital in Scotland and co-author of Superyoung (1999), men and women who reported having sex an average of four times per week looked approximately 10 years younger than they really were."

I wonder if this is because they had more, or the reason they had more..... hmmmm. damn statistics

According to the article:

"Sex results in a more youthful appearance. According to a study by Dr David Weeks, a clinical neuropsychologist at the Royal Edinburgh Hospital in Scotland and co-author of Superyoung (1999), men and women who reported having sex an average of four times per week looked approximately 10 years younger than they really were."

I haven't read the cited study, but is it really having sex that makes you look younger or isn't it rather looking younger that will make the odds higher that you get more sex in the first place...?

I would have though the top entry in a list of reasons for sex would be:

To make babies!

What can I say? Happily married, and having a good time!

As I understand it, the question is actually asking what the biological basis is.

The short answer is that creatures that don't live in water can't really manage external fertilisation, like many sea creatures do. This just pushes the problem back one step: Why reproduce via fertilisation?

And the answer to that is that it deepens the gene pool. In a creature with 22 chromosomes then, assuming no crossovers, there are (2^22)^2 genetically possible offspring, as opposed to the 1 genetically possible offspring provided by asexual reproduction.

Deepening the gene pool protects our species from harmful genetic mutations, as well as from diseases which target monocultures.

On the basis that sex does all those wonderful things for you, I was considering who might benefit most. Who would be the most youthful, healthy, happy and content people in our society. The answer was obvious to me, prostitues.

Now are they sure they're being absolutely scientific in this and clear in their language that just sex is doing all this good?

The real scientific reason for sexual reproduction is the mixing of successful genetic mutations which greatly accelerates the progress of evolution so creatures who reproduce sexually are complex successful organisms. Organisms that do not have sex have not made the same evolutionary progress. Basically have sex because it is an evolved characteristic that helps us adapt to our environment.