Selective pressures leading to bipedalism in our ancestors and us
Essay, Anthropology
Write an essay that identifies and discusses the many selective pressures leading to bipedalism in our
ancestors and us.
Project description
Even though some primates can move bipedally for short distances, walking on two legs is one of
humanity’s defining characteristics. We are a bipedal primate — a hominid. Write an essay that identifies
and discusses the many selective pressures leading to bipedalism in our ancestors and us. You should
depend on your readings, the videos, and on discussions
READINGS that need to be included in the writing!!! Very very important that everything is backed up
with these (along with any other research that you may need to do) but it is IMPORTANT THAT IS
INCLUDED!!
Book: Lucy’s Legacy. Some scientists see the sun rising and setting on their particular species, while
others ignore that same species. There is a big rift between one of the authors of your book, Donald
Joahnson, and the Leakey family, particularly the patriarch, Richard Leakey. Also keep in mind that I am
simplifying the number of species that were are actively considering, especially in my charts that are
attached to this and the next LM.
DVD: This is the time to take a hard look at Part One in the Becoming Human trilogy. These are the DVDs
you bought for the class. That First Steps portion of the DVD looks at the evidence for our break with
the “missing link” and the appearance of the first true hominids to inhabit the mother continent of us
all, Africa. You will hear and see a good deal about this early creature named Ardipithecus ramidus as
well as some of the other competition for the earliest known hominid honor.
? PLEASE LET ME KNOW IF YOU CANNOT FIND THIS ONLINE OR ANYWHERE!
This is a chart that I put together in regard to earliest possible hominids. Quite possibly one or all of
these specimens knew the missing link, the creature that spawned the ancestors of us, the chimp, and
the gorilla. I suspect the first three species, Toumai, Millenium Man, and Ardi are the most promising.
And they may all be at base of our ancestry. There likely were a whole suite of creatures in Africa during
this early era, waiting for natural selection to do its thing.
I hear the ancient footsteps like the motion of the sea
Sometimes I turn, there’s someone there, other
times it’s only me
Bob Dylan
Ancient Rocker
Most Ancient Hominids….
Genus and Species Age Location Discoverer
Sahelanthropus tchadensis 6-7 MYBP Chad, Central Michel Brunet
(Toumai) Africa (France)
Orrorin tugenensis 6 MYBP Tugen Hills, Martin Kenya Pickford
(Millennium Man) Brigitte Senut
(France)
Ardipithecus ramidus 4.4 MYBP Ethiopia Tim White
(Root Ape, aka “Ardi”) (US) and Ethiopian Colleagues
Australopithecus anamensis 4 MYBP Kenya Meave Leakey
Australopithecus afarensis 3.1 MYBP Ethiopia Donald
Johanson
(US)
Yves Coppens
(France)
VIDEO http://proxyau.wrlc.org/login?url=http://www.american.edu/customcf/catalog_video.cfm?
callNum=8482577_10
Me To You – Learning Module 3
–Fossils–
–The Big Break Up–
–First Hominids–
This is another three-part M2Y, and I hope it will help you make the transition to a better understanding
of the hominid fossil record. But first I want to say something about the very nature of fossils and also
set up the split of hominids along with the ancestral gorilla and the ancestral chimpanzee from our
common parent, the so-called missing link. Like before I’ll subdivide to avoid confusion.
Fossils and Fossilization
You should be aware that the objects we study – often referred to as bones – aren’t really bone at all.
Instead they are fossilized bone, precise copies of the original living bone (latter often referred to as
green bone). Green bone just doesn’t last long. It is organic and it biodegrades in most environments.
For example, a human body interred on the AU quad (I’m not suggesting anything) will have mostly
completely disappeared within about 400 years. Bacteria within the organism itself and in the soil
recycle once living tissue and bone rather quickly. Acids in the soil likewise play a major role in the
disintegration process. Insects can also do their part. If scavengers can get to the remains everything
becomes broken as well as scattered and is likely exposed to the elements, thus further hastening
destruction. In short, from the beginning the odds are against preservation of organic remains.
It is possible, however, to beat those odds if the original green bone can become fossilized.
Fossilization can happen in two ways. First, if the original green bone can become encased in sediment it
sometimes forms a mold of sorts as it disintegrates. Under proper conditions that mold may fill in
naturally with minerals thus making a copy of the original. The famous Taung Baby, an immature
Australopithecus africanus, was preserved for us in that way. I excavated some human burials a number
of years ago where the soft tissue of the brains had been replaced by exact copies made of sediment,
the general shape and all the surface folds being preserved in great detail. That’s one way to get a
fossil.
Second, another way involves a molecule-by-molecule infiltration process. In this case elements present
in the surrounding depositional environment replicate the original green bone, transforming it into a
fossil. This is the preferable process, and if you ever have a chance to pickup a fossilized bone you will
see that it has the weight of a rock instead of that of bone. But it is an exact copy of the original.
Without fossils we would know little of the past.
Just remember, however, that the fossilization process is rare, and it is a selective process. A number of
things have to happen:
1) An organism has to die (obviously);
2) The plant or animal can’t be recycled by the environment. It must remain mostly intact;
3) It has to be gently buried in sediments and those sediments must contain replacing minerals that will
infiltrate and fossilize the green bone;
4) The fossilized bone then must just as gently be uncovered or exposed;
5) A paleontologist or archaeologists then has to find the fossil(s).
Those last two steps are very important. To find fossils you must go to places where they are exposed,
not where they remain deeply buried within the earth’s crust. Quarries often give such good exposure,
and that is where some of the first early hominids were recovered in the southern part of Africa. Areas
that have a great deal of erosion or geologic uplift can also be good locations to look for fossils. The
Great Rift Valley of eastern Africa, where that part of the continent is trying to tear off and move out
to sea toward Madagascar, is another good spot. Eastern Africa has yielded many of the most
spectacular early hominid fossils. Even there, however, fossil hunting is a tedious business. Mary and
Louis Leakey searched for about 29 years in Olduvia Gorge before turning up significant hominid fossils.
People in a hurry do well not undertake fossil hunting, even in the best of circumstances.
And we should always remember that fossilization is a rare and selective process. It favors those
creatures that perish in good depositional environments. That’s why many of the fossils one sees were
once marine species. It does not favor those species that lived on land. For example, you are all familiar
with the dinosaur, Tyrannosaurus rex. Of the 25 or so relatively complete T. rex sets of remains that
have been recovered, only four are more than 60 percent complete. Sue, the magnificent T. rex, now on
display in the Field Museum in Chicago is the most complete (about 90 percent). That is remarkable
given that it has been 67 million years since she perished. As for our early ancestors, the same is true
even though time is not as great. We must remember that the fossilization process only offers a glimpse
into our past, and through that lens we are probably seeing only a selective sample of what once
walked ancient Africa and other nearby continents. For
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