Human Evolution

[ed_pardo]

The question has come up in a recent thread as to which ape is the common ancestor of Pan and Homo. Searching for an answer I have come up with a short list of possibles. But to illustrate the logic behind my thoughts I have included the ones that I don't think will fit the picture as well. To get an idea of the relationships and dates please see:

Lineage-Specific Gene Duplication and Loss in Human and Great Ape Evolution, Fortna et.al. 2004
PLoS Biology | http://biology.plosjournals.org)

The following are listed from youngest (pliocene) to oldest (miocene). I have left out the Oligocene to Eocene genera as there is way too much dispute in that area (this area is too controversial already). You will see an asterisk next to each genera or species that has been shown to be capable of fully upright (erect) locomotion. They are also in bold type.

Pliocene:

Gracile australopithecines* shared several traits with modern apes and humans and were widespread throughout Eastern and Southern Africa as early as 4.4 to as late as 1.7 million years ago. A. robustus, is a heavily built creature, represented by specimens from southern and east Africa and existed 2.2 to 1.2 (a narrower 1.9 to 1.5 million years ago (mya) by other estimates (Lemonick & Dorfman, 1999)).

Kenyanthropus platyops - KNM-WT-40000 Discovered by Meave Leakey and her team in 1998 west of Lake Turkana, Kenya, K. platyops is described in the March 2001 issue of Nature as a new genus dating back to the middle Pliocene, 3.5 mya., challenging A. afarensis “Lucy” as the direct ancestor of modern humans. Skull includes right temporal bone with mandibular fossa and mastoid process. [Smithsonian]

Late Miocene:

Sahelanthropus tchadensis - (6-7 mya). Nicknamed Toumai, has caused great debate among scientist since this specimen appears to be more human-like than any other known fossil hominid in its age span yet still possesses several primitive primate features. It is still undetermined as to weather this species was bipedal or walked on all four limbs. [ Smithsonian ]

Oreopithecus* (7-9 mya) large-bodied hominoid. [ MEIKE KO HLER & SALVADOR MOYA-SOLA, 1997, "Ape-like or hominid-like? The positional behavior of Oreopithecus bambolii reconsidered" ]

Dryopithecus, suggested to be sister (clade) to Oreopithecus and considered as a vertical climber and suspensory ape or if some or all of these features are instead related to bipedal activities. [ ibid ]

Middle Miocene:

Nakalipithecus (~10 mya) very close to the last common ancestor of gorillas, chimpanzees and humans [ "Rare great ape fossil challenges evolutionary theory", November 12, 2007, CHICAGO (AFP) ]

Chororapithecus (10-10.5 mya) ancestors of the modern day gorilla. [ "Ethiopian fossil find pushes human-ape split back millions of years", Marlowe Hood, Aug 23, 2007, AFP ]

Pierolapithecus* (13 mya) last probable common ancestor to humans and great apes had a body like an ape, fingers like a chimp and the upright posture of humans. [ "Ape fossil bridges evolutionary gap", Diedtra Henderson, Nov 19, 2004 ]

Proconsul africanus existed between 14 and 23 million years ago during the Miocene epoch. This species is one of the better represented early Hominid species due to the numerous specimens that have been excavated. [ Smithsonian ]

Morotopithecus* (over 20 mya) [ Nathan M. Young, Laura MacLatchy, 2003, "The phylogenetic position of Morotopithecus" ]; [ Aaron G. Filler, 2007, "Homeotic Evolution in the Mammalia: Diversification of Therian Axial Seriation and the Morphogenetic Basis of Human Origins" ]

Looking at just fully bipedal apes and a time for the split at 4.1 to 6.1 mya, the only genus that meets the criteria (that we know of) is Australopithecus.

The website for Dr. Filler's "Upright Ape": http://uprightape.net/index.html
The paper published by PLos is http://uprightape.net/Homeotic_Evolution.pdf

[kristina3313]

In regards to "Sahelanthropus tchadensis" why would it be a big deal that some its skull features were closer to genus Homo than the genus Austrolopithecus, it is because of the age of the fossil?

[ed_pardo]

In regards to "Sahelanthropus tchadensis" why would it be a big deal that some its skull features were closer to genus Homo than the genus Austrolopithecus, it is because of the age of the fossil?

Yes, That is what they are thinking and if we use that logic then Lucy isn't a human ancestor but rather a chimpanzee ancestor. But remember that Australopithicenes were diverse and somewhere in that mixture are chimps and humans, it's hard to tell one from the other at that point. Also there is confusion because of semantics. So it is quite possible that Lucy is Pan and we have not identified our particular lineage but it would be within the early Australopithicenes IMO.

I'm still looking at this as well. I am hoping that by fielding the issue in an open forum we could get an exchange of ideas and some clues where to look for the answers.

[ed_pardo]

The issue of the pelvis of the "Lucy" fossil has been brought up as being more Homo than Pan. Rosenberg points out:

Assisted birth has likely been around for millennia, possibly dating as far back as 5 million years ago when our ancestors first began walking upright, according to University of Delaware paleoanthropologist Karen Rosenberg. .... When our ancestors evolved to begin walking on two legs, Rosenberg says, this upright posture created a wide but short opening in the pelvis in which the baby must travel, requiring a new form of birth so that the baby could find its way through a now tight birth canal.

"Anthropologist's Studies Of Childbirth Bring New Focus On Women In Evolution", ScienceDaily (Feb. 25, 2009)
http://www.sciencedaily.com/releases/20 ... 173043.htm

In support of the event timing, from "Demographic Histories of ERV-K in Humans, Chimpanzees and Rhesus Monkeys", Paolo M. de A. Zanotto, Marco Aurelio B. Corsini, Edward C. Holmes, Fernando L. de Melo, Camila M. Romano:

Since all partial sequences we dismissed were likely generated by incomplete purging events it is evident that our approach has underestimated the loss of ERV proviruses. Nevertheless, by investigating complete genomes were able to estimate integration times, which is only possible when both LTRs are present. The Bayesian skyline plot for HERV-Kshowed a conspicuous population bottleneck in the last 17 MY, comprising a significant reduction in complete proviral numbers up until 4MYBP, after which a cladogenetic burst within ERVs from Group N [9] took place. This population bottleneck could indicate a recent loss of ancient signal in the hominids, since the difference in the skyline signatures predates the split of Homo and Pan. Possibly, bottlenecks since the Plio-Pleistocene may have played an important role, facilitating both the loss of unfixed alleles and the fixation of deleterious ones by genetic drift [28], and which could help explain the observed complex dynamics of HERV-K. Intriguingly, the time frame for a “recolonization” of the hominids by Group N HERV-K at around 1.5 MYBP coincides with the emergence of human-specific life history traits [23], such as increased generation time.

http://www.plosone.org/article/info%3Ad ... ne.0001026


Lovejoy nicely illustrates the relationship, in "The natural history of human gait and posture, Part 1. Spine and pelvis",

Fig. 5. Frontal projections of hominoid pelves. (A) chimpanzee; (B) AL-288-1; (C) human female; (D) human male. Note the dramatic shortening of the ilia in the hominids and the absence of any dorsal projection that might “entrap” the last lumbar (L5 in humans; L6 in A. afarensis). Note the much closer geometric similarity of AL-288-1 to the human male than female, despite its very large interacetabular distance (a female character in modern humans). The human pelvis has been entirely remodeled so as to greatly enlarge its birth canal. Note the extremely broad sacra of the hominids in comparison to the very narrow one of the ape (©L.B. Spurlock).

The paper is available (open access) at
http://rivernet.ncsu.edu/courselocker/P ... osture.pdf
(I apologise for not being able to post the illustration, the paper is an embedded PDF)

Those can also be compared with the pelvis of H. erectus (below)

A reconstruction of the 1.2 million-year-old pelvis discovered in 2001 in the Gona Study Area at Afar, Ethiopia, that has led researchers to speculate early man was better equipped than first thought to produce larger-brained babies. The actual fossils remain in Ethiopia. (Credit: Scott W. Simpson, Case Western Reserve University)

Pelvis Dated To 1.2 Million Years Ago Shows Ancestors May Have Been Born With Big Heads
ScienceDaily (Nov. 14, 2008)
http://www.sciencedaily.com/releases/20 ... 181152.htm

IMO this places Lucy into our lineage.

[secularhumanizinevoluter]

WO, I must confess to absolute AWE at Kristina and your ability to follow that bit about the DNA and where the split took place. Rather like being in the Homeric Greek class they laughingly put me in when I made my abortive stab at higher edgejumakation(THAT spelling IS a joke).
Whether Lucy and her group were a dead end or are included in our lineage from the Pelvis it always appeared clear to me that this animal was going in another direction from the apes. I never understood based on the fossils themselves how it could be postulated that after becoming bipedal an animal would devolve back to knuckle walking?

[ed_pardo]

That bothered me also Sec. I think that Filler [1] hit it in his paper about back problems. [2] I'm sure that you must have seen the article about that middle eastern family that have to walk on all fours because of a genetic "defect". That "defect" may be the commonality that goes all the way back to Morotopithecus, having caused families and entire tribes of prehumans to revert IMO.

Emergence and optimization of upright posture among hominiform hominoids and the evolutionary pathophysiology of back pain

Aaron G. Filler, M.D., Ph.D., F.R.C.S.
Institute for Spinal Disorders, Cedars-Sinai Medical Center, Los Angeles; Center for Advanced Spinal Neurosurgery, Santa Monica, California; and Museum of Comparative Zoology, Harvard University, Cambridge, Massachusetts
Abbreviation used in this paper: PSIS = posterior superior iliac spine.

The lordotic region of the lumbar spine is a significant focus of pain and dysfunction in the human body, and its susceptibility to disorders may reflect its substantial reconfiguration during the course of human evolution. The basic anatomy of the lumbar vertebra in Old World Monkeys and Early Miocene apes, or proconsulids, retains typical mammalian architecture. The lumbar vertebra in humans is different in the repositioning of the lumbar transverse process dorsal to the vertebral body rather than originating on the body itself and in the loss of the styloid process that is adjacent to the facets in other primates. These two features appeared in Morotopithecus bishopi 21.6 million years ago, suggesting that this ape is the founder of an upright hominiform lineage. The iliocostalis lumborum muscles migrated onto the iliac crest approximately 18 million years ago, becoming a powerful lateral flexor muscle of the trunk. The posterior superior iliac spine shifted far dorsal to the longissimus insertion in the genus Homo between 1 and 2 million years ago, making this muscle a powerful extensor of the lumbar spine. Functionally, the establishment of strong muscular flexors and extensors adds dynamic compressive stresses to the lumbar disks and also makes these muscles susceptible to strain.

[1] http://anthropology.net/2007/12/15/a-hu ... -the-apes/
[2] http://thejns.org/doi/pdfplus/10.3171/FOC-07/07/E4

[ed_pardo]

A comparison of wrists belonging to Pan, Homo sapiens and Homo floriensis:

from "New Light Shed On The 'Hobbit', ScienceDaily (Sep. 25, 2007) "
http://www.sciencedaily.com/releases/20 ... 145353.htm

The research asserts that modern humans and our closest fossil relatives, the Neandertals, have a very differently shaped wrist in comparison to living great apes, older fossil hominins like Australopithecus (e.g., "Lucy") and even the earliest members of the genus Homo (e.g., Homo habilis, the "handy-man"). But the hobbit's wrist is basically indistinguishable from an African ape or early hominin-like wrist--nothing at all like that seen in modern humans and Neandertals.

From the Smithsonian
http://si-pwebsrch02.si.edu/search?q=ca ... d&oe=UTF-8

The team turned its research focus to the most complete of the 12 skeletons discovered and specifically toward three little bones from the hobbit’s left wrist. The research asserts that modern humans and our closest fossil relatives, the Neandertals, have a very differently shaped wrist in comparison to living great apes, older fossil hominins like Australopithecus (e.g., “Lucy”) and even the earliest members of the genus Homo (e.g., Homo habilis, the “handy-man”). But the hobbit’s wrist is basically indistinguishable from an African ape or early hominin-like wrist - nothing at all like that seen in modern humans and Neandertals.

empahsis added - ep

[ed_pardo]

For an idea of where these bones fint into the human anatomy, these are links to illustrations from Gray's Anatomy:

Bones of the Proximal Row (upper row).—The Navicular Bone (os naviculare manus; scaphoid bone)

http://www.bartleby.com/107/illus220.html

The Capitate Bone (os capitatum; os magnum)

http://www.bartleby.com/107/illus227.html

The Lesser Multangular Bone (os multangulum minus; trapezoid bone)

http://www.bartleby.com/107/illus226.html

[secularhumanizinevoluter]

I don't know about anyone else but the Hobbit wrist bones look like a pretty good halfway point between chimp and human.

[ed_pardo]

I don't know about anyone else but the Hobbit wrist bones look like a pretty good halfway point between chimp and human.

I agree. So from what the Smithsonian says about it being like an Australopithecus "(eg. Lucy)" I would surmise that the Pan lineage split well before Lucy's time but still possibly within the early Australopithecus/Parenthropus lineage around 4.2-4.4 mya (not real sure on this as there is something still missing between 4.4 and 5.0 mya IMO).

[kristina3313]

The pelvis pic is great, I like how they used a computer software to give a full picture. I wonder if you have Lucy's fossil remain image, somewhat similar to the pelvis one. It's very neat though, how now you can illustrate exactly what you are talking about, remember you were telling me before to look up stuff in Grey's Anatomy book .

[kristina3313]

In regards to "Sahelanthropus tchadensis" why would it be a big deal that some its skull features were closer to genus Homo than the genus Austrolopithecus, it is because of the age of the fossil?

Yes, That is what they are thinking and if we use that logic then Lucy isn't a human ancestor but rather a chimpanzee ancestor. But remember that Australopithicenes were diverse and somewhere in that mixture are chimps and humans, it's hard to tell one from the other at that point. Also there is confusion because of semantics. So it is quite possible that Lucy is Pan and we have not identified our particular lineage but it would be within the early Australopithicenes IMO.

I'm still looking at this as well. I am hoping that by fielding the issue in an open forum we could get an exchange of ideas and some clues where to look for the answers.

That is exactly what I was trying to say on the other thread, that if Lucy was a chimpanzee ancestor, then there shouldn't be such a big deal that she had more of a chimp characteristics than that of a human.

[ed_pardo]

Kristina
In the "pelvis" post above, top link, Lovejoy's paper illustrates AL-288-1 (A. afarensis). I just could not post the illustration because of the way it is stored in a PDF. Click on that link ans scroll down through the PDF several pages to see the picture.

[ed_pardo]

Kristina,
I located a better illustration whicl includes pelvis, femur and foot for comparison:

Australopithecine pelvises are far more similar to humans than to those of apes, and shows that they were undoubtedly bipedal. The pelvis of Lucy (A. afarensis), although not shown here, is very similar to that of A. africanus. Despite the overall similarity, australopithecine pelvises are not identical to those of humans. There are a number of differences, some of which are more obvious when viewed from other angles. This illustration is from "Humankind Emerging", edited by Bernard Campbell.
http://www.talkorigins.org/faqs/homs/pelvis.html

[ed_pardo]

As I mentioned earlier, there are many australopithecine fossils and much debate about which ones are related. These are my picks (just an opinion).

Taung 1, "Taung Child", Australopithecus africanus



The large rounded brain, canine teeth which were small and not apelike, and the position of the foramen magnum(*) convinced Dart that this was a bipedal human ancestor, which he named Australopithecus <apith.html> africanus (African southern ape). Although the discovery became famous, Dart's interpretation was rejected by the scientific community until the mid-1940's, following the discovery of other similar fossils.

Sts 5, "Mrs Ples", Australopithecus africanus



It is the best specimen of africanus. It is about 2.5 million years old, with a brain size of about 485 cc.

http://www.talkorigins.org/faqs/homs/sp ... ouvp12/130

Five characters separate man from other hominoids—a large neocortex, bipedality, reduced anterior dentition with molar dominance, material culture, and unique sexual and reproductive behavior. Evidence provided by the fossil record, primate behavior, and demographic analysis shows that the traditional view that early human evolution was a direct consequence of brain expansion and material culture is incorrect, and that the unique sexual and reproductive behavior of man may be the sine qua non of human origin.

The Origin of Man, C. Owen Lovejoy
http://www.sciencemag.org/cgi/content/a ... 1/4480/341

The following paper supports the time frame for A. garhi IMO:

According to Stedman et al., mutation of the MYH16 gene and loss of its functional protein product, by significantly reducing the force production capability of the muscles of mastication, not only led to the dramatic gracilization of the skull evident in post 2.5 million-year old Homo, but may have also permitted its subsequent marked increase in
cranial capacity.

Of muscle-bound crania and human brain evolution: The story behind the MYH16 headlines
Melanie A. McCollum, Chet C. Sherwood, Christopher J. Vinyard, C. Owen Lovejoy, Fred Schachat
http://home.gwu.edu/~sherwood/2006.MYH16.Reply.JHE.pdf

However it is now believed that A. garhi, although more advanced than any other australopithecine, was only a competitor species to the species ancestral to Homo and therefore not a human ancestor. ... ... The cranial capacity of A. garhi measures 450cc, the same size as other australopithecines. The mandible classified as Asfaw et al. has a morphology generally believed to be compatible with the same species, yet it is possible that another hominin species may have been found within the same deposits. Studies made on the premolars and molar teeth have a few similarities with those of Paranthropus boisei since they are larger than any other gracile form of australopithecine. It has been suggested that if A. garhi is ancestral to Homo (ie. Homo habilis) the maxillary morphology would have undergone a rapid evolutionary change in roughly 200,000 and 300,000 years.

http://en.wikipedia.org/wiki/Australopithecus_garhi

Named in the April 23, 1999, issue of Science, the large research group that discovered the finds made some broad claims and supposition that is definitely not accepted by all ... The type specimen of the species is BOU-VP-12/130, an associated set of cranial fragments comprising the frontal, parietals, and maxilla with dentition. ... These specimens are important no matter what the eventual final attribution, due to the fact that the remains are from East Africa at a time when there is very little remains (2.0-3.0 myr). ...
One of the more striking features of the A. garhi remains is the size of the postcanine dentition, which is at or beyond the nonrobust australopithecine or A. robustus extremes. This is the only feature that suggests any link to the robusts, and as such it is very unlikely that the specimen is in any way derived from or is a sister species to robustus. This is seen especially in the large size of the anterior teeth, exceeding those of the largest australopithecines and far exceeding the robusts, who are marked by anterior tooth reduction or stasis. Based on tooth size, the garhi material seems to fit well with schemes that see either one or both of africanus and afarensis as a direct human descendent, as the canine-to-premolar/molar size ratios are comparable to both species and early Homo. ...
Specific cranial attributes include:
The lower face is prognathic with procumbent incisors.
Canine roots are placed quite laterally to the nasal aperture margin.
The premaxillary surface is separated from the nasal floor by a blunt ridge and is transversely and sagittally convex.
The palate is vertically thin.
The zygomatic roots originate above P4/M1.
The dental arcade is U-shaped, with slightly divergent dental rows.
The temporal lines encroach deeply on the frontal, past the midsupraorbital position and likely met anterior to bregma.
The postglabellar frontal squama is depressed in a frontal trigon. The localized frontal sinus is limited to the medial one-third of the supraorbital surface.
There is marked postorbital constriction.
The parietal bones have a well-formed, bipartite, anteriorly positioned sagittal crest that divides above lambda.
Cranial capacity of approximately 450 cc (reconstructed).

http://www.archaeologyinfo.com/australo ... sgarhi.htm

Australopithecus garhi (2.5 million years ago)
Species Description:
Australopithecus garhi may represent an evolutionary link between the genera of Australopithecus and Homo. Circumstantial evidence suggests that A. garhi may have been the earliest tool user. Antelope fossils excavated from the same site as A. garhi show cut marks made by a stone tool; both the hominid and antelope fossils are dated at 2.5 million years old. The earliest stone tools, thought to be 2.6 million years old, were found nearby in Gona, Ethiopia.

http://www.pbs.org/wgbh/evolution/human ... ind/h.html

There is no direct evidence that A. garhi used stone tools, but the proximal cutmarked bones provide circumstantial evidence. ... A. garhi may represent an evolutionary link between the genera of Australopithecus and Homo. It is probably descended from A. afarensis and adds a potential ancestor for the genus Homo. The remains are from the time when there are very few fossils, between 2.0-3.0 mya. ...
The type specimen is ARA-VP-12/130, an associated set of cranial fragments, frontal, parietals, and maxilla with dentition. The teeth are larger than those of the earlier A. afarensis. Its braincase, face and palate are more primitive than those of later Homo. The known specimens demonstrate that the thigh bone had elongated a million years before the Homo forearm shortened. The derived human-like humeral/femoral ratio together with the ape-like upper arm to lower arm ratio evidence the mosaic-like evolution of the features that characterize modern humans.



Comparison of chimpanzee, A. afarensis and human dentition.
Photo courtesy IHO/Kimbel.

http://www.jqjacobs.net/anthro/paleo/garhi.html

I would have preferred a picture of the A. garhi detention for comparison but no luck in finding one.

[secularhumanizinevoluter]

Ed, I LOVE you mannnn! The shot of the three palates is pure gold. That and the three drawings of the pelvises, although I would MUCH prefer the actual bones/fossils to make the comparrison from.
Kristina, in Lucy's Child there IS a reconstructed Lucy skeleton like you were wondering about. It is absolutely beautiful.
After looking at the palates I am more convinced that Lucy belongs in our dirsct family lineage.

[secularhumanizinevoluter]

What a beautiful arch!!!

[ed_pardo]

What a beautiful arch!!!

I thought you would appreciate that shot pf the dentary.

I did notice something odd in the roof towards the rear. The orifice of the auditory tubes are much larger in proportion than either chimp or human.

[JackronRM]

It's all very nice, Ed. But it still doesn't rule out that the evidence also points to completely separate species. The specimens are NOT "indisputeably" 'mediatory'. You're all 'speculating' (even BELIEVING) that they are, because you are heavily biased and brainwashed towards that result, but, from where I stand, it's a different story and open to different interpretations.
If you were honest with yourselves, and as truly 'openminded' as you like to say and think you are, you would not be so ready to accept such weak evidence as 'factual'.

[ed_pardo]

Jack
They ARE totally seperate species. They are even seperate genera. If they were all the same species that would in fact falsify the TOE. What you are looking at in these pictures and those in the linked papers, are stages seperated by thousands to millions of years. What we are looking at are the differences within the similariities to find a progression. Australopithecines are probably the most hotly debated hominid fossils ever found with the possible exceeption of the Hobbit. Some are ancestral to humans but some are ancestral to chimps, the question is which ones. This is why I really like the Hobbit fossils. They have so many affinities to both us and australopithecines but continued to evolve on their own, from a habilis or erectus ancestor, until 10,000 years ago. Paleoanthropologists normally use dentary to follow the progression because they have an earmark signature (which is why I knew Sec would like the dentary shot). But just look at that erectus pelvis and tell me it's not human.