I am dumb, I am aware. If twins have the same DNA, are they the same person from a biological standpoint?
There exists such a thing as gene-environment Interaction. The older twins get, generally the more different they are becoming.
This article is behind a paywall, but provides some more information.
Edit, here is a better link.
Thank you for the reading! I didn’t know that your genes could be affected by your environment. I haven’t had a chance to read the article yet, but do you know if this would lend any credence to the nature vs nurture argument when it comes to personality, and whether socio-psychological factors in the environment can affect gene expression?
It isn’t really nature vs nurture, it’s nature interacting with nurture. Steve Jones, the biologist explained it beautifully with reference to Siamese cats:
Siamese cats are light brown with dark brown fur at the tips of their ears, feet and tail. But if you raise one in a very warm environment, they will be light brown all over. A very cold environment, they will be dark brown all over. There’s a gene switching the fur colour but its action depends on the temperature.
There are many different ways genes and environment interact, there’s no real ‘argument’ here. It is simply true and, because genes and environment are often so closely linked, it’s often complicated and sometimes impossible to tease out what’s causing what.
This is the field of epigenetics. We all have a lot of genes, but the environment and past family trauma can determine which genes are on or off.
No, they are biologically separate individuals. For example:
- If one twin takes a drug, the other twin’s body is not thereby affected by that drug.
- If one twin learns a piece of information, the other twin does not thereby learn it.
- If one twin suffers an injury or disability (e.g. breaking a leg), the other twin remains uninjured.
- If one twin goes on a calorie-restricted diet while the other does not, only the first twin will lose weight.
Two organisms grown from fertilized eggs with the same DNA are still two different organisms. Their biological processes (e.g. metabolism) are not directly affected by one another; so they are biologically not the same individual.
This is the most enlightened comment here. OP look no further.
I love how your brain works.
Thank you for answering! I think what I was getting at with my question was more asking if at birth (or at some point in conception) on a molecular level, are twins identical clones of each other, with identical structures in their cells. Obviously as they grow they diverge, but are they from identical source material?
I don’t know why my brain decided to have this existential confusion today, so I apologize for my ignorance
DNA spells out how your cells work. But it doesn’t control what environment you interact with. What you learn depends on your environment, not your DNA: for example, if twin babies are separated at birth and one grows up with English-speakers and the other grows up with Polish-speakers, one would be fluent in English and the other in Polish. They’re clearly not “the same person” even if they’re running the same cellular source code.
Put another way: If you and I are running the same browser on the same OS, that doesn’t mean I know all your passwords.
While they share the same DNA at fertilization, the environment starts to alter the DNA and its expression (how the DNA is processed). So you end up with two persons who share a very large amount of their DNA (large amount of what is not common among all humans anyway) but still differ, even if you ignore any discussion of free will, consciousness and such. The environment has an even greater influence after birth. There is even a debate, wheter the environment has a greater impact than the DNA.
Thank you for your answer! I had no idea that environment plays a factor in how your DNA is expressed! That’s super mindblowing to me, thank you so much!
Not really no… even from a “single” cell point of view they inherit different biological junk that floats in the extracellular fluid of the mother (forgot the name, probably transcription factors). Also you should specify homozygote twins cuz twins can be of different sex! Anyhow… they share all DNA 100% but that doesn’t make them “the same”. Even in utero they might be exposed to different, albeit.small, stimuli. Maybe one is receiving slightly more nutrients bc he’s attached first etc etc. Life is so complicated that there’s many different things that can change! So then after birth they will still be exposed to similar but not identical environments and stimuli. They will eventually diverge and can, and do, become very different individuals, even from a mere biological pov.
I’m learning so much in this thread! So even in the womb, there exists different stimuli that can affect gene expression in identical homozygous twins? What other kinds of stimuli could that consist of? I know you said difference in absorbed nutrients, but what other things can affect gene expression? Changes in pressure? like for example, could the mom sleeping on one side for a certain duration of time cause changes in blood flow to the fetuses, etc? Thanks for putting up with all my questions, haha
It’s not very scientific of me to make these claims, I apologize. I’m not an expert in fetus development… I’m not sure these differences of stimuli matter in womb so much as to affect gene expression, but we can’t really exclude them, can we? That’s what I’m getting at. To be identical, these twins must undergo an identical development, which is impossible.
At a single point in time, sure, but then they diverge and are never the same.
No, they also have different fingerprints, different iris, can have different hair, etc
No, not even at a genetic level. This study, for example shows: “International researchers have compared the external ears of more than 1,400 people of multiple nationalities and found that the ear is as good an identifier of an individual as a fingerprint or DNA, and can even distinguish between identical twins.”
That reads to me like the ears are affected differently by the environment (including in the womb). Also the numbers in that article suggest there are over 5 million “collisions” in which two people have ears that their test would say match.
That’s so crazy to me! But I’m guessing if they could match, there must be some margin of error in the test
Indeed. Some of the margin of error is probably needed since I’m sure ears change over time on the same person if they are measuring that closely
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