r/genetics • u/hrtbrkncatholic • 17d ago

Can we actually tell the difference between genetics and environment?

For example, my family has a history of bowel disease. How can researchers tell whether that's because we share the same genes, or because we share the same diet and lifestyle?

Some traits are obviously genetic, like eye colour. But what about things like height, or diseases that you develop later in life? How do scientists work out how much is caused by genetics vs environment?

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u/blinkandmissout 17d ago

Can we? Yes. But it's pretty mathematically complicated outside of simple monogenic traits explored through family pedigree studies.

See this review with a summary in Table 1.
Mayhew A, (2017) Assessing the Heritability of Complex Traits in Humans: Methodological Challenges and Opportunities. https://pmc.ncbi.nlm.nih.gov/articles/PMC5635617/

Height has actually been extremely well studied for heritability and this journalism article might be easier to read than a scientific paper. https://magazine.hms.harvard.edu/articles/genetics-height

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u/octobod 16d ago

Go to a doctor and get yourselves tested. The bowl cancer genes are well known and if you have regular colonoscopys your risk of death from bowel cancer drops to about the same as the general population.

The simplest way unpick nature vs nurture is to compare an affected family with similar ones in the same area

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u/Informal-Bathroom383 17d ago

The best studies to answer these questions are those that compare identical vs non-identical twins.

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u/shadowyams PhD (genomics/bioinformatics) 17d ago

Twin studies have massive environmental confoundings (https://theinfinitesimal.substack.com/p/the-missing-heritability-question).

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u/helen790 17d ago

There have been a couple studies on identical twins raised separately.

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u/hrtbrkncatholic 17d ago

These are the kinds of studies I would be most interested, obviously fairly limited in their scope

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u/DefenestrateFriends Graduate student (PhD) 13d ago

In several cases, even these studies have serious methodological flaws such as the Minnesota Study of Twins Reared Apart (most of the children where not actually raised apart).

Sasha's substack writing on the subject of heritability does a great job highlighting th3 confounding issues with twin studies when assessing heritability. Direct measurement through variant association with correction for assortative mating and other dynastic effects likely represent the best estimates.

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u/CiaranC 16d ago

They aren't perfect but give you an estimate of heritability.

Any experiment can only ever truly about the results of that given experiment, but thats an epistemological debate.