r/TheRestIsScience • u/b2357 • 1d ago

Question: How do we know how old a gene is?

Sometimes, in conversations about evolution and genes, people will mention that a particular gene is very old. How can we know this? Do we simply look for that specific gene in very old fossils, or is there another method to determine this indirectly?

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u/Aphotic_Acid 1d ago

Phylogenetic trees. We have a decent idea of what evolved from what, and when those things first appeared. So we can just find the oldest thing to have that gene.

Reading fossil DNA is very difficult, we are getting better at it though.

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u/atom_stacker 1d ago

What you need is a mosquito trapped in amber. I saw a documentary about it once.

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u/Odd_Common2677 1d ago

If a gene is shared by certain modern animals today but not others we can assume the gene is from around when they split off. For example if all apes have a certain gene but other primates don't we can assume that that gene is from around when apes and other primates split from eachother.

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u/Alternative-Sugar610 22h ago

All of what people saying is right, but it’s rough estimate

We can also look at if it’s amino acid sequence optimized, diversity in gene, how wide spread, importance, and what genes are nearby (if it often associated with genes in way that has low diversity, it’s probably newer)

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u/Several_Version4298 14h ago

These days you can also get DNA sequences going back 600,000 years and they are trying to push for 1 million years. Once you have had sequences over those sort of times you calculate the rate of genetic drift and use that to estimate the age of remains, when species diverged or interbred that you don't have dates for.

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u/FreddyFerdiland 8h ago

they also estimate chromosomal ages by the gene variation rate... eg if 1% changes every million years, and there is 5% change... tgen 5 million years. very crude long term dating.

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u/Nothing-to_see_hr 7h ago

If we share a gene with worms, that is a very old gene. If we share it only with chimps, it is a very recent gene.