From the wiki link above:
It often takes a long time for new scientific knowledge to make its way to schoolteachers.
Thank you all.
The question arose from various recent nature shows.
Just a few days ago, I heard, “Chimpanzee’s closest relatives are Humans”.
This was like Discovery Channel or History Channel.
I don’t know why they dumbed it down so far, but thank you for educating me further on the Chimp vs Bonobo thing
Biology, like time, is infinitely divisible and any attempts at sorting into neat compartments are due to our wanting to bring order out of chaos. All mother nature cares about is whether any progeny will yield fertile offspring (he says while watching one of the ducks chase the goose around).
Interesting thread.
After twenty or so serious replies, is it ok yet to bring up Ernest Borgnine?
I’ve heard these factoids before, though never in the same sentence. Though I appreciate the fun, it also wouldn’t hurt to be sure I actually understand.
I think what the DNA testing services are referring to is how many mutations the siblings share, relative to the most common or default version of each gene. And, what National Geographic or our biology textbook, or whoever it was, meant was how similar the most common or default versions for two different species are to one another.
Is that approximately right, as a resolution of this seeming paradox?
The figures are referring to two different things. The 50% figure isn’t a measure of how genetically similar two individuals are to one another, but rather how much of their DNA they share by descent from a common ancestor. How genetically similar they are will depend in part on how genetically similar their ancestors are. For example, two individuals whose parents are part of the same ethnic group will be more similar than ones whose ancestors are from different parts of the world.
The other figure just compares how similar the genetic sequences are, regardless of descent. Many genetic loci are invariant or show low variability, and so the percentage of similarity across the entire genome will be high.
When considering fairly similar genomes, one approach is to align all homologous sequence (sequence with common evolutionary ancestry, however far in the past), and then look at single nucleotide differences within those aligned sequences. Although this ignores other types of differences, including gross changes such as the chromosome fusion in the human lineage, it is a useful approach because single nucleotide mutations occur frequently with a uniform distribution through time, providing a quantitative measure of genetic diversity within a species (which is related to population size) or genetic divergence between species (which is related to the time since the speciation event at which the evolutionary lineages of the two species diverged).
Using this measure, the average single nucleotide difference between two unrelated human individuals is 0.1%-0.4%, reflecting our fairly small historical effective population size. The range is wide because some human subpopulations are more diverse than others. The single nucleotide divergence between any human and any chimp is about 1.2%, reflecting the mutations that have accumlated since the human and chimp lineages diverged.
When we say that a brother and sister “share 50% of their DNA”, we mean that half of their genomes have immediate common ancestry from their parents, and are therefore completely identical in sequence (excluding de novo mutations). The remaining 50% has the same single nucleotide divergence as two unrelated humans, in the 0.1%-0.4% range mentioned above - still far more similar to each other than to a chimpanzee.
The tests only compare the current DNA. How can the test tell the reason behind the similarity of the sequences?
The 50% figure for the relationship of siblings doesn’t come from comparison of their DNA. It’s just the mathematical result of the fact that you get half your genetic material from each parent. It says nothing about the similarity between the DNA that came from each parent.
For a short sequence, it can’t. But across the genome, reduced diversity due to low population diversity looks different from reduced diversity due to close familial relationship.
In each chromosome you get a mixture of the DNA of both grandparents on that parent’s side. But it’s not a “finely chopped” mixture - there will be a very long stretch from one grandparent spliced to a very long stretch from the other grandparent, with only a few splices per chromosome.
So for a brother and sister, you don’t see 50% fewer differences spread evenly throughout the genome. You see a long stretch where the DNA came from the same grandparent and the sequence is exactly the same; then a long stretch where the DNA came from different grandparents and the sequence divergence is just like two unrelated people (assuming that the grandparents are not inbred).
bonobo is closer than humus office spacius
Think of it this way. Let’s say humans are 4th cousins with chimps and 5th cousins with bonobos, and that the chimps and bonobos are first cousins. Our closest relative would be the chimps and the chimps closest relative would be the bonobos.
No. Read the thread.
There was once a common ancestor of all three. That single ancestral species split ~7 million years ago into two ancestral species - one lineage led to humans, the other was the common ancestor of chimps & bonobos. Much later, the common ancestor of chimps and bonobos split into two separate lineages.
If you think about the topology of that tree, the evolutionary divergence time between humans and chimps must be exactly the same as the time between humans and bonobos.
Better yet, think of it in a way that’s correct. We’re equally close to both chimpanzees and bonobos.
More to the point, the fact that one taxonomist reclassified bonobos in 1933 doesn’t mean that bonobo species status was generally accepted in the field of primate taxonomy in 1933, or by the… whatever the animal equivalent to the IAPT is called.