For example i have read that obesity is 70% genetic and personality traits like happiness, thrill seeking, shyness, etc are 50-60% genetic.
However, what does that mean exactly? I always assumed it meant that (for obesity for example) 70% was genetic, 30% was free will and environment. No matter what your free will and environment that only made up 30% of the equation. However does that 30% entail just passive, relatively non-effective environments (ones that do not play a major role in the development of say obesity and personality traits) or does it involve the most cutting edge research in things like psychology, social psychology and pharmacology?
Take that 70% obesity figure i put above. That was determined by studying identical twins who were seperated at birth and their respective obesity levels. However, there were some problems with taht 70% figure because the environments of the twins were identical almost. Most seperated identical twins both grew up in the same country (the US), and the same city. So both had unlimited access to things like pepsi and high fat desserts. Another study that took into account radical lifestyle differences (ie, one was a marathoner and one was a couch potato, one lived an ameican lifestyle one lived a hunter gatherer lifestyle) found genetics only had a 10-20% role in obesity. the other 80-90% was controllable by environment, if you include surgery that number is probably even lower. So i’m confused, is obesity (as an example) 70% genetic or 10% genetic? Also, does this apply across the board? Are all ‘genetically inherited traits’ closer to 10% genetic when you include the most advanced surgical/pharmacological/psychological treatments or is that 50-60% mark set in stone?
In my own personal experience take happiness. I am genetically prone to depression (my mom has had it, dad has had it, at least one of my two brothers has had it and i have had it). I have also had bad life events that have brought about severe depression. HOwever i also study alot about the new psychology of happiness and the pharmacology (through OTC supplements) of happiness. I am now relatively happy most of the time but i still have depression ‘waves’. When scientists say that happiness is 40% non-genetic, i don’t know if they include the idea that i will study OTC supplements and research and apply them to my life or if they just assume i am passively sitting by and letting life happen to me.
I dont know if this belongs in GD or GQ. I’m mainly just wondering if, when scientists say something is X% genetic do they mean that the other percentage (say 40% non-genetic influences for happiness) are passive or does that include the most cutting edge psychological and pharmacological advances?
Yeah this probably belongs in GD, not GQ.
Also with obesity, obesity is easier to treat than depression. Depression can be due to a number of biochemical factors, obesity just involves burning more calories than you take in. So the fact that radical lifestyle changes can overcome most of obesity’s genetic component may not apply to other, more complicated traits like shyness.
To clarify the terminology: the scientific results are usually stated something like “60% of the variation of the attribute is due to genetics”. This means when comparing individuals of a population, 60% of the difference among the individuals is from genetics. This is not the same as saying “60% of the attribute is due to genetics”.
The rest is the environment. That is, everything external to the individual. Whether that includes surgery or pharmaceuticals depends on what variables the researchers for a particular study factored out or left in. Sometimes there’s no substitute for actually reading the journal articles.
Eh - I think you’re either misunderstanding the results of the studies you’re reading, or the studies are misrepresenting their results with statistics (which is really, really easy to do, as any statistician will tell you.)
It’s really impossible to determine to what degree genetics is involved in obesity by looking at one study (as in your first example) or worse yet, one case study which seems to be what your second story is.
In order to really make any sort of statement with any sort of validity a large study, involving many people from many different backgrounds would be required. If you had read such a study, it would probably be safe to extrapolate the results to the population as a whole - you could not, however, extrapolate the results to yourself.
That’s one of the problems with epidemiological population studies - great for populations, not so good for individuals who actually wind up reading the damn things.
They’re talking about the R[sup]2[/sup] value of the model. That value indicates what percentage of the variation in the dependent variables is due to variation in the independent variables.
In the case of obesity and genetics, the genetic factors are the independent variables, and the presence/absence of obesity is the independent variable.
What does it mean for you? Well, not much. All you can say is that if most of your immediate family is obese, there’s a pretty good chance you’ll have to worry about it too.
That’s not to say that you can’t make statements about individual measurements from a model; it’s just that those statements are going to involve “maybe” and “probably” quite often.
One of the modules in my biology course is Genetics, and I remember there is a heritability of a trait, which helps selective breeders determine how likely a parent is to pass on their phenotype to their offspring.
V[sub]p[/sub] = V[sub]g[/sub] + V[sub]e[/sub]
Which means that phenotypic variation can be accounted for by both the sum of effects of genetic variation (e.g; genes for being tall) and the environmental effects (e.g; vitamin deficiency that makes you grow less).
The heritability of a trait is the proportion of variation due to an indivual’s genes,
(broad sense) heritability = V[sub]g[/sub]/V[sub]p[/sub]
That last ‘equation’ doesn’t really make much sense to me, because there are no numerical values, so I think it’s just meant to be an easier way of remembering what heritability is.
Right, I’m sure my answer is totally irrellivant to the OP, but I’ve got a genetics exam on friday so I need all the practise I can get!
Regards,
Harry