Human Evolution

Updates

February 8, 2019: Smithsonian. Link here.

The sites:

• Hadar, Ethiopia, heart of Africa: 2.36 mya
• Turkana, south of Hadar: 2.09 mya
• Olduvai, south of Turana: 1.90 mya
• Two branches:
• to the northwest: Dmanisi, 1.85 mya
• to the north and then a sharp right turn to the east, to Asia
• Yuanmou, Indochina, 1.71 mya
• then another split
• to the north, central China coast, Nihewan, 1.66 mya
  
• to the south, Strait of Malacca, Sangiran, 1.66 mya

The four main groups:

• the oldest, 6.5 mya to 4 mya: the Ardipithecus group
• then, 4.5 mya to 2.0 mya: the Australopitchecus group
• then, somewhat contemporary with Australopithecus, 2.8 mya to 1.0 mya, the Paranthropus group
• then, finally, somewhat contemporary with Paranthropus, 1.0 mya to the present, the Homo group

Genetics suggest an ancestor species in our lineage that we have yet to identify.

The research suggests that "the mysterious hominin" was likely descended from an admixture of Neanderthals and Denisovans (identified as a unique species in 2010).

Such a species in our evolutionary past would look a lot like the fossil of a 90,000-year-old teenage girl from Siberia's Denisova cave. In 2018, the remains were considered the only known example of a first-generation hybrid between the two species, with a Neanderthal mother and a Denisovan father.

Ancient interspecies liaisons: introgressions.

Neanderthals: originated in Africa but spread as far north as the British isles, and as far east as Uzbekistan, throughout the Middle East.

Denisovans: ranged from Siberia to southeast Asia and may have survived until as recently as 30,000 years ago. Denisova Cave in Siberia. 

I believe the current thinking is that "humans" spread north to eastern Eurasia, and broke into two groups, the Neanderthals and the Denisovans. It would only make sense that there might be descendants of inter-racial mixing.

See this article: how DNA genes can be turned on and off -- a molecular knob, as it were: methylation, which silences gene expression. In methylated DNA, one nucleotide, cytosine, degrades of tousands of  years into a different product than usual. By trading that degradation in an ancient genome, scientists can create a methylation "map." Scientists use this method to further elucidate evolution of the Denisovanian "girl."

So, still a little confused: was this teenage girl found in that Siberian Denisovan cave, a pure-bred Denisovan or a Neanderthal/Denisovan hybrid. It sounds like the latter, which makes it incorrect to refer to her as Denisovanian.

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Original Post

Link here to a Scientific American Article, April 4, 2010.

For the past 48 hours I have been in an anthropology frame of mind. For future reference, I am posting this, based on the "Human Pedigree" article by the anthropology editor for Scientific American, Ms Kate Wong,  January, 2009, issue of Scientific American. My photocopy is hard to read, so there may be some errors, but this is how I interpret what I can make out.

The story starts seven (7) million years ago with Sahelanthropus tchadensis, first found in Chad, in 2001, and believed to be the earliest hominid.

A hominid bone of Orrorin tugenensis, believed to be six (6) million years old, has been found but it's relevance has not yet been determined. It's not part of the human pedigree. At least not yet.

Five and a half (5.5) million years ago, the first hominid ancestor appears, Ardipithecus kadabba, leading to Ardipithecus ramidus (4.5 mya) and Australopithecus anamensis (4.3 mya) and then to Lucy, Australopithecus afarensis (3.2 mya). About the same time, a contemporary, Kenyanthropus platyops (3.4 mya) appeared on the scene. The latter evolved into Homo/Kenyanthropus rudolfensis (1.8 mya) but dead-ended there. Homo/Kenyanthropus rudolfensis was a contemporary of Homo habilis, Homo ergaster, Paranthropus robustus, and Paranthropus boisei.

Lucy branched at least four times. One branch dead-ended 2.5 mya with Australopithecus garhi. Another dead-ended about the same time with Australopithecus africanus. Two branches lasted longer.  ***  One branch led to Paranthropus aethiopicus (2.4 mya) which divided into two branches, both of which dead-ended about the same time, 1.8 mya, and were noted above: Paranthropus robustus and Paranthropus boisei. Lucy's fourth branch led to Homo habilis which appears to have dead-ended 1.8 mya as a contemporary of at least three, maybe four, other hominids.

*** Australopithecus sediba, discovered in 2008, is believed to have descended from Lucy, and was a link to Homo.  In 2010, A. sediba received much press coverage as the "missing link."

However, a common ancestor (Australopithecus sediba?) after Lucy, about 2 mya branched into Homo habilis (dead-ended, as noted) and another yet unidentified ancestor (1.8 mya) divided into two branches, one leading to Homo ergaster (1.6 mya) which led to Homo antecessor (0.8 mya), then Homo heidelbergensis (0.5 mya), which ultimately branched twice, about 0.3 mya, one branch leading to Homo neanderthalensis, appearing about 100,000 years ago and dying out about 25, 000 years ago. The other branch from Homo heidelbergensis eventually evolved into Homo sapiens, appearing as a contemporary of Homo neanderthalensis, and still here today.

Much earlier, the common ancestor that branched off to Homo ergaster, also branched off to Homo erectus, appearing about 100,000 years ago, and a contemporary of Homo neanderthalensis, and possibly a contemporary of Homo sapiens.

The only other hominid in this chart is Homo floresiensis, which came from a common ancestor of Homo erectus and was also a contemporary of the Neanderthals, modern man, and Homo erectus.


Significant ancestors:

1. Sahelanthropus tshadensis: believed to be the earliest hominid (7 mya).
2. Australopithecus aferensis (Lucy): common ancestor to four branches, including the species Paranthropus and the species Homo, contemporaries.
3. Homo habilis: "handyman" -- first hominid known to have made tools.
4. Homo ergaster: the first hominid to have left Africa. 
5. Homo neanderthalensis: a big-game hunter that ruled Ice Age Europe and Asia for 200,000 years
6. Homo floseiensis: the latest surviving extinct hominid with startlingly small brain and body

On a "direct line":

Sahelanthropus tschadensis (7 mya) --> Ardipithecus kadabba (5.5 mya) --> Ardipithecus ramidus (4.5 mya) --> Australopithecus afarensis (Lucy) (3.2 mya)  --> Homo ergaster (1.8 mya) --> Homo antecessor (0.8 mya)--> Homo heidelbergensis (0.5 mya)--> Homo sapiens.

Homo habilis was  a "descendant" of Lucy, but dead-ended as a contemporary of Homo ergaster.

Homo neanderthalensis was a "descendant" of Homo heidelbergensis, but dead-ended as a contemporary of Homo sapiens.

The newly discovered hominid estimated to be about 2.5 million years old would be the common ancestor descended from Lucy and before Homo habilis; perhaps he/she is the common ancestor to the two longest-surviving species that descended from Lucy: Paranthropus and Homo.

Paranthropus (Greek for "beside" as in "along side" "human"): lived alongside Homo.

Side note: Lucy was discovered by Dr Donald Johanson in 1974. I remember that story well; I was still at an impressionable age and I was very interested in anthropology. I read his book (I still have it). In 1974 I would have been 23 years old and in my second year of medical school at the University of Southern California.