From the title through the posthumous shoutouts, a great piece of writing. Thanks for illuminating these percentage differences. I've hankered to understand that for a while; your explanation cleared it right up for me.
Love your substack - your writing is excellent and you have fueled a real curiosity in me to learn more. Wondering if you might provide a recommendation of a good genetics primer for a someone who is willing to put in the time to understand genetics more fully. I can follow along with your writing but a next level understanding would do well for me. Any ideas would be welcome - and if other readers have found good references for genetics understanding I would be please to those as well!!
Thank You for this well understandable summary ! Some 20 years back I saw an author write of Homo sapiens as "the human animal". I felt this embarassing, yet I wanted to understand why. For many years I was surprised to learn how much great Apes behave like 'us'. Now, when considering our human dealing with our natural environment and amongst ourselves, my view is changing: I more and more see how much "we" still behave like "them". Obviously it's a very looong way for us to outgrow our heritage... or to accumulate enough 'fixed mutations' to no longer kill ourselves so easily. I suppose the next version of hominin will do so.... at least some of the survivors... I'm an optimist, am I not ?
Rousing piece and I strongly endorse the sentiment of striving to find more simply because we can. I have a question regarding the 23andMe shared segments point you made.
In your haplogroup piece you mentioned how the chromosome I receive from each parent is actually a mish-mash of the two chromosomes that parent has at that location due to genetic recombination during meiosis.
My question is, how then can 23andMe claim that I share the entire chromosome at precisely the same locations with my parent when those locations have been messed up by the genetic recombination ?
I would be interested to hear from you on as to what types of genes most commonly differ, and by how much (i.e , between us and chimps)? Genes related to:
Immune function,
Muscle fiber strength,
BRCA and other DNA repair genes,
Mylen sheath composition genes,
O2 uptake by hemoglobin as a function of pH,
Etc.
I.e. is it necessarily things we might expect to be most different? and What are the real surprises?
How comparable are the differences between us and chimps, us and Bonobos, and chimps and Bonobos... Etc.
So... you’re saying there is a chance a part of Homo naledi lives inside us!
Other people have already said it, but this is beautiful. Sincerely, this is spiritual. We do owe it to those who came before us to tell their stories to the best of our abilities. I don’t understand how everyone is not obsessed this stuff. I’m glad I reread this tonight. Another thing that’s spiritual, and pretty trippy, is being able to compare your DNA with your sons DNA. That must have been a really cool experience for you to have.
Your explanation of Identity by Descent--defined as a matter of “tracking genetic ancestry within shallow genealogies or pedigrees”--seems unsatisfactory. The shallowest genealogy is one generation, which would have one sharing roughly half one’s genes with a parent but none with a grandparent. But the actual assumption is that one shares roughly ¼ with a grandparent, 1/8 with a great-grandparent, etc., indefinitely far back (though petering out eventually because the number of genes is finite). No one relies on a concept based on “shallow genealogies.”
There’s a great mystery about chromosome number that I have posed in blog comments to several geneticists and never gotten a serious answer. How does the number of chromosomes change in a way that gets fixed within a group without automatically causing both speciation and a very tight genetic bottleneck?
Are there any species which are recognized as a single interbreeding species with a common gene pool, where the haploid number varies as it does between chimps and humans?
If so, is that the general case for situations like the chimp-human divergence, where maybe differential cross-fertility leads to a natural sorting into groups that quickly lose the ability to interbreed, perhaps because chromosome fusion-fission sites diverge too much?
If not, then how is an extreme bottleneck avoided?
I used to think that the 48 vs 46 human chromosome count was a shocking example of scientific groupthink, but I recently looked more carefully at the history, and maybe not quite. My reading is that mainly it was that until the 1950s basically nobody really cared about the number, though indeed one guy in the 1920s reported the human number as 48. It appeared in textbooks, so outsiders assumed it was True, but the (known to insiders) somewhat crappy original estimate was left alone mainly because it didn't seem an important question.
From the title through the posthumous shoutouts, a great piece of writing. Thanks for illuminating these percentage differences. I've hankered to understand that for a while; your explanation cleared it right up for me.
Inspiring
Hi Razib,
Love your substack - your writing is excellent and you have fueled a real curiosity in me to learn more. Wondering if you might provide a recommendation of a good genetics primer for a someone who is willing to put in the time to understand genetics more fully. I can follow along with your writing but a next level understanding would do well for me. Any ideas would be welcome - and if other readers have found good references for genetics understanding I would be please to those as well!!
Thank You for this well understandable summary ! Some 20 years back I saw an author write of Homo sapiens as "the human animal". I felt this embarassing, yet I wanted to understand why. For many years I was surprised to learn how much great Apes behave like 'us'. Now, when considering our human dealing with our natural environment and amongst ourselves, my view is changing: I more and more see how much "we" still behave like "them". Obviously it's a very looong way for us to outgrow our heritage... or to accumulate enough 'fixed mutations' to no longer kill ourselves so easily. I suppose the next version of hominin will do so.... at least some of the survivors... I'm an optimist, am I not ?
Rousing piece and I strongly endorse the sentiment of striving to find more simply because we can. I have a question regarding the 23andMe shared segments point you made.
In your haplogroup piece you mentioned how the chromosome I receive from each parent is actually a mish-mash of the two chromosomes that parent has at that location due to genetic recombination during meiosis.
My question is, how then can 23andMe claim that I share the entire chromosome at precisely the same locations with my parent when those locations have been messed up by the genetic recombination ?
Thanks
I would be interested to hear from you on as to what types of genes most commonly differ, and by how much (i.e , between us and chimps)? Genes related to:
Immune function,
Muscle fiber strength,
BRCA and other DNA repair genes,
Mylen sheath composition genes,
O2 uptake by hemoglobin as a function of pH,
Etc.
I.e. is it necessarily things we might expect to be most different? and What are the real surprises?
How comparable are the differences between us and chimps, us and Bonobos, and chimps and Bonobos... Etc.
So... you’re saying there is a chance a part of Homo naledi lives inside us!
Other people have already said it, but this is beautiful. Sincerely, this is spiritual. We do owe it to those who came before us to tell their stories to the best of our abilities. I don’t understand how everyone is not obsessed this stuff. I’m glad I reread this tonight. Another thing that’s spiritual, and pretty trippy, is being able to compare your DNA with your sons DNA. That must have been a really cool experience for you to have.
Your explanation of Identity by Descent--defined as a matter of “tracking genetic ancestry within shallow genealogies or pedigrees”--seems unsatisfactory. The shallowest genealogy is one generation, which would have one sharing roughly half one’s genes with a parent but none with a grandparent. But the actual assumption is that one shares roughly ¼ with a grandparent, 1/8 with a great-grandparent, etc., indefinitely far back (though petering out eventually because the number of genes is finite). No one relies on a concept based on “shallow genealogies.”
This was a fun read Razib
There’s a great mystery about chromosome number that I have posed in blog comments to several geneticists and never gotten a serious answer. How does the number of chromosomes change in a way that gets fixed within a group without automatically causing both speciation and a very tight genetic bottleneck?
Are there any species which are recognized as a single interbreeding species with a common gene pool, where the haploid number varies as it does between chimps and humans?
If so, is that the general case for situations like the chimp-human divergence, where maybe differential cross-fertility leads to a natural sorting into groups that quickly lose the ability to interbreed, perhaps because chromosome fusion-fission sites diverge too much?
If not, then how is an extreme bottleneck avoided?
I used to think that the 48 vs 46 human chromosome count was a shocking example of scientific groupthink, but I recently looked more carefully at the history, and maybe not quite. My reading is that mainly it was that until the 1950s basically nobody really cared about the number, though indeed one guy in the 1920s reported the human number as 48. It appeared in textbooks, so outsiders assumed it was True, but the (known to insiders) somewhat crappy original estimate was left alone mainly because it didn't seem an important question.
I still don't know the difference between Identity by descent and identity by state. Maybe I'm just dim, and you explained it. Maybe you didn't.