Human evolution. Fascinating subject - where did we come from? History of Primates: - evolved from shrews during Cretaceous (so an older order) about 65 mya. - Some characteristics of primates: - clavicle well developed (allows increase flexibility, supports arms). - five digits, front and rear. Often thumb (and big toe) opposable. - claws -> nails - lots of skin receptors in fingers. - snout shortened (sense of smell is less important - Why?). - usually only one pair of mammary glands - excellent vision, well developed nervous control, often increased intelligence. - Several orders and suborders. In general, lemurs, a few smaller groups such as bush babies and tarsiers, old world monkeys, new world monkeys, and humans & great apes (sometimes gibbons are included with the great apes) [Fig. 34.37, p. 726]. - Origin of humans [Fig. 34.40, p. 729]: - your text says nothing about most of the species in this figure! - some preliminary remarks. There is a lot of controversy here. Some of it just plain silly (i.e., is species x part of the genus Homo or the genus Australopithecus ). - much of it also has to do with which species are thought to be ancestral to humans, and which are not. We'll see some of this. [Note: many of the following figures are not in the text. Most can be found on the web] - a possible common ancestor for both humans and apes (i.e. split from rest of primates): - no way to prove this, but might be Proconsul or something like it. Shows many features of both humans and great apes - roughly 18 mya. - On the other hand, a few years ago: - Sahelanthropus tchadensis, or Toumaë (meaning hope of life in the local language. - discovered in northern Chad. - 6-7 million years old. - fairly complete skull. - thought to be a hominid, and therefore possibly our ancestor (far too early to be sure, though). - bipedal? no one is sure.
- some folks consider this a common ancestor between us and the great apes. - Orrorin tugenensis, from about 6 mya. This is another possible human ancestor, though a bit more recent than Sahelanthropus. - Strangely, there is some evidence that this may be more human than some of the Australopithecus species (generally considered on the line to humans) - found in Kenya - definitely bipedal, and a forest dweller (meaning the origins of bipedalism may need to be re-examined.) - Ardipithecus ramidus - 4.4 million years ago, possibly up to 5.8. - until recently, the oldest known hominid. - possibly bipedal, up to four feet tall. - skull fragments and teeth. - Australopithecus anamensis - 4.2-3.9 million years ago. - partial leg bones indicate bipedalism. - human like humerus. - skull primitive, skeleton more modern. - Now, the first really well known fossil: Australopithecus afarensis. - Also known as Lucy. - from about 2.8 to 3.8 mya. Original fossil (Lucy) discovered in Ethiopia, but since then others (parts of up to 300 individuals) have been found in East Africa. Footprints in the Olduvai gorge. - bipedal, small brain (about 400cc), large canines, projecting jaw, but still a good climber. - disproved an old theory about large brains evolving before bipedalism. - no stone tools survive, but may have used wood or other things that don t preserve well. Australopithecus seems to have branched into two (three?) lines 1) more Austrolopithecines such as A. aethiopicus, A. robustus, and A. boisei. The genus name Paranthropus is sometimes used for these [Isn t it great that folks can t make up their minds?]. - these are generally agreed not to be ancestral to humans. - lived at the same time as our ancestors, but were much more vegetarian. - had more robust skulls. - A. aethipicus was probably the ancestor of the other two. - cranial capacities of around 530 cc., except for A. aethipicus, which was around 410 cc. 1 1/2) Australopithecus africanus. There is some thought that this may have been ancestral to modern humans, though most folks would disagree. May have given rise to the other species of
Australopithecus. - generally more graceful appearance & lighter build. - cranial capacity between 420 and 500 cc. 2) the genus Homo (possibly via yet another Australopithecine, Australopithecus garhi, about which not much is known): The genus Homo (our genus): Homo habilis. - 1.3-2 mya - face projects even less. Teeth smaller, jaws smaller & less muscular. - larger cranial capacity, 700-800 cc. - still a good tree climber. - TOOLS! crude stone tools can be dated from this time. - suggestions from fossils are that large animals were not used much for food yet. - East Africa. Homo rudolfensis?? (debatable) - if this is a real species, then very similar to Homo habilis. Many folks consider this to be Homo habilis. Quite a bit of controversy surrounding this. Homo ergaster?? (debatable) - A slightly more primitive form of Homo erectus (see just below). - Possibly transitional between H. habilis and H. erectus, but some evidence that they were still around when H. erectus showed up. - Again, a lot of controversy here, as some folks say this is simply Homo erectus. Homo erectus - 300,000-1.5 mya. - some recent finds indicate they may have lasted until 50,000 years ago, and thus overlapped with more modern humans (this is part of the controversy around Homo ergaster ). - first known hominoid found outside Africa ( Java man. Peking man ), though most fossils (and the oldest) still from Africa. - 850cc - 1200cc cranical capacity. (1200 is kind of high). - Much like us, but different in: - smaller brain/more massive jaw/eyebrow ridges/ sloping forehead/sloping chin. - probably could not really talk yet in the sense of having a conversation like us. - most complete fossil is still being analyzed (has yielded much information so far), but is of a young boy about 11 to 13 years old - over 60% complete (found in Kenya).
- more advanced tools, fire, large animal bones associated with camps. - most likely ancestral to us, though a few folks will say that Homo ergaster is our ancestor. More modern humans (still a lot of controversy). Homo heidelbergensis (somewhat debatable) - basically a more archaic form of Homo sapiens. - appear between 800,000 and 500,000 years ago. - seem very transitional between Homo erectus and Homo sapiens (these forms have characteristics of both, and are difficult to classify as either Homo erectus or Homo sapiens). This is the reason Homo heidelbergensis is often used now for these specimens. [NOTE: the transitional nature of these specimens seems to suggest that Homo erectus is definitely our ancestor, contrary to what some folks suggest about Homo ergaster.] - cranial capacity of around 1200 cc. - still some skull features that are more robust than modern human, though not as much as in Homo erectus. Homo sapiens neanderthalensis: - =Homo neanderthalensis according to some authorities. - very much like modern human. Probably not directly ancestral, but it appears that we do share a lot of genes (this changes regularly depending on the most recent study!) - note that this is OUR species, but a different subspecies (this obviously controversial). - burial of dead, highly crafted tools. - eyebrow ridges, bigger (being bigger means you need bigger brains. Since these were essentially modern humans, they did have slightly bigger brains than us (1450 cc, but not increased intelligence)). - did they have modern speech?? - 35,000-130,000 years ago. - Properly dressed, they wouldn t stand out in a crowd today. Homo sapiens sapiens. - Cro-Magnon and modern humans. - Cave paintings, evidence for culture, etc. - no anatomical differences between Cro-Magnon and us - modern in all respects. The term merely refers to older humans. - 100,000 years ago to present. - displaced Neanderthal, possibly by interbreeding in some areas, though recent evidence seems to discount this. - brain capacity about 1350 cc. - so story now goes from biology into history - civilizations etc.
Can we make any sense of the above, rather confusing picture? Here is a possible evolutionary tree that might help keep things straight. The question marks (?) indicate the more controversial parts [NOTE: THIS MAY NOT LOOK RIGHT UNLESS YOU USE A NON- PROPORTIONAL FONT (E.G. COURIER) WHEN YOU PRINT IT]. Homo sapiens (incl. neanderthals) Homo heidelbergensis??????????? Homo erectus A. boisei A. robustus?? Homo ergaster?? Homo Homo habilis Australopithecus aethipicus rudolfensis?????????????????? Australopithecus africanus? Australopithecus afarensis? Australopithecus anamensis? Ardipithecus ramidus??????????? Orrorin tugenensis Sahelanthropus tchadensis Some concluding remarks about human evolution.???? Proconsul africanus???? - Obviously, there is a lot of controversy. Unfortunately, much of it not friendly. The differing factions often dislike each other. - if you look around web, the authors viewpoint will be obvious. Don t be surprised if you run into something that doesn t look much like what was presented here. Even the Smithsonian is doing things differently. Incidentally, even though they have strong opinions, they have an excellent web site: http://www.mnh.si.edu/anthro/humanorigins/ha/a_tree.html