John Hawks Profile picture
Sep 19, 2020 5 tweets 2 min read Read on X
Generally, human chromosomes are numbered in order of length. Chromosome 1 is the longest, then 2, and so on. Most people know the sex chromosomes are exceptions; X is longer than 8, Y shorter than 20. Fewer know that chromosome 20 is longer than 19. And 22 is longer than 21. Human karyotype illustratio...
In the 1950s and 1960s, there was a lot of diversity in how different research groups numbered human chromosomes. Length was an obvious criterion, but to reliably sort karyotypes, scientists had to rely on additional characteristics including centromere position and arm lengths. Chromosome numbers from Lej...
The human genetics community worked to standardize the nomenclature of chromosomes in the 1960s, settling on today's numbers, before methods of measuring chromosome length were precise enough to accurately rank relative lengths of the shortest chromosomes.
The methods quickly progressed during the 1960s but the early nomenclature stuck. Growing work on important karyotype variants like trisomy 21 (Down syndrome) meant that a standard way of referring to chromosomes was more valuable than having the names match their lengths.
A full chart of human chromosome lengths in nucleotides (based on EBI data). The other blip in the order is chromosome 10, which is shorter than 11. Bar chart showing human chr...

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More from @johnhawks

May 17, 2023
Quite like the new paper by my @UWMadison colleague @apragsdale. Fun to see lots of people newly discovering these ideas about metapopulation models! A couple of notes:
nature.com/articles/s4158…
An implication of this population model is that the structure of our species, Homo sapiens, began to emerge several hundred thousand years earlier than the dispersal that led to Neandertal and Denisovan populations.
When added to other evidence of recurring gene flow between Neandertal and African ancestral populations, this very strongly implies that Neandertals are Homo sapiens.
Read 5 tweets
Mar 18, 2022
So this seems very unpopular for some reason, but humans DID evolve from apes. We did not evolve from chimpanzees, gorillas, or any other living apes. They are our cousins. Our close fossil relatives were like living great apes in many ways and more like humans in others. MRD skull of Australopithecus anamensis on the right with a
Today's great apes, including chimpanzees and bonobos, two species of gorillas, and three species of orangutans, are a small surviving remnant of the diversity of apes that once existed. Each evolved in ways that helped them survive, just as our ancestors did. Tree showing the diversity of living great apes and humans.
Paleontologists have discovered many more forms of extinct apes than living ones. They were adapted to their time and place, some Asian, some African, and some European, but did not survive to the present day. Many of them lived in the period before 5 million years ago. Chart showing today's apes on a tree with time of existence
Read 7 tweets
Dec 8, 2021
Some discussion in comments last week in @ScienceMagazine about "paleodemes" with a short defense of the value of the concept. I think the paleodeme concept has most of the problems of paleo species concepts with none of their benefits. science.org/doi/10.1126/sc…
The person probably most responsible for the paleodeme concept in human origins is Clark Howell, whose 1999 paper "Paleo-Demes, Species Clades, and Extinctions in the Pleistocene Hominin Record" defined (although it did not first introduce) the concept. journals.uchicago.edu/doi/abs/10.108…
As presented by Howell, a paleodeme corresponds to a regional sample of fossils across a delimited range of time, with some morphological distinctiveness. These were groups like "Neandertal", "Skhūl/Qafzeh", or "Petralona/Atapuerca-Sima".
Read 5 tweets
Aug 13, 2021
Interesting paper on cutmark evidence from Olduvai, further substantiating early access to animal carcasses by tool-wielding Early Pleistocene hominins. @SciReports nature.com/articles/s4159… Cutmark evidence on animal bones from Olduvai Gorge, from Do
The paper's discussion raises lots of reasons why the anatomy of early Homo supports the idea that they were competent hunters. On this I don't disagree, but I think that focusing on "early Homo" here is misleading for several reasons.
First, "early Homo" fossils overlap substantially in anatomy with Australopithecus and Paranthropus. So much that we cannot always tell them apart (including long-standing arguments about well-known and not-so-fragmentary fossils).
Read 9 tweets
Jun 25, 2021
So, Homo longi. It's such a good name. Dragon people. And an amazing skull discovery. Adds to our knowledge of the Middle Pleistocene in China. But it's sad that the name is not going to stay. cell.com/the-innovation… Harbin skull viewed from the front. Photo by Wei Gao, from T
The boring reason why we can't use the Homo longi name is technical. The research puts the Harbin skull together with the Dali skull, and Xinzhi Wu gave that the name Homo sapiens daliensis more than 40 years ago. So IF there's a species, it has to be H. daliensis. Phylogenetic morphology analysis of Harbin skull, showing it
In case you wonder how close Harbin looks to Dali, here is Harbin on the left and Dali (which has some crushing to the maxilla) on the right. As Weidenreich might have said, they resemble each other as closely as one egg resembles another. Harbin skull (left) compared with Dali skull (right)
Read 13 tweets
Jun 24, 2021
The new report of fossil material from Nesher Ramla, Israel, claims a "previously unknown archaic Homo population" some 140,000 years ago. It's a big claim in an area where most scientists have thought that early modern humans and Neandertals interacted. science.sciencemag.org/content/372/65… Mandible from Nesher Ramla. From Hershkovitz et al. 2021 htt
Looking at the morphology of the mandible NR-2, it falls within the variation of fossils attributed to Neandertals, and is similar to Krapina, which is around the same age, and Sima, which are early Neandertals. This seems like a basic early Neandertal jaw. PC plot showing position of Nesher Ramla 2 next to Neanderta
The other fossil NR-1 is a complete right parietal bone and fragments of the left parietal. The analysis of shape places is near late Neandertals and early Neandertals, but a bit less "barrel-shaped", thereby similar to generalized H. erectus and African Middle Pleistocene Homo. PC plot of Nesher Ramla 1 parietal bone showing its position
Read 11 tweets

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