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Author Topic: How do we trace human evolution?  (Read 4794 times)

Offline hamza

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How do we trace human evolution?
« on: 01/07/2011 20:24:25 »
Ok, I am having a bit of difficulty understanding the concept of human evolution particularly, and their descent from some common ancestor shared by chimpanzees and bonobos.  I would like to be enlightened about the concept of fossil records that are millions of years old and how they prove that we humans arose from them. This confusion arises in me from the fact that if we consider our present times and take the skeletons of a chimpanzee and a human, then they do have similar features and morphology but obviously they are different species as we know of them  now.  So how does some million year old fossil prove that it were an ancestor rather than some completely different entity present at that particular time.  What if it were some old distinct species, extinct by now, just like dinosaurs. What is the key feature that determines a descent from an ancestor to progeny.  Please put some light on the explanation of an ancestor to human transformation, that I am completely na´ve about.
« Last Edit: 07/07/2011 22:44:37 by chris »


 

Offline CliffordK

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Re: How do we trace human evolution?
« Reply #1 on: 02/07/2011 01:47:14 »
When you look at homo sapiens (humans), the oldest fossil and the origin of the species dates back to about 200,000 years ago.  There are numerous different sources of data that points to the origin of the species about this time, including the Mitochondrial Eve, or the common shared ancestor for all the mitochondria DNA passed down exclusively from females, and the best estimate of the age of this female ancestor based on DNA mutation rates.  Y Chromosome Adam, the common ancestor for the male lineage actually is somewhere between 60,000 and 142,000 years ago.

So, the question is what came before modern man.  And, thus archeology has been pushing back the limits of our knowledge of human ancestry. 

And, human-like fossils have been identified dating back 5 to 10 million years ago, certainly showing up on Earth long after the Dinosaurs had died off about 65 million years ago.

I believe at this point, the oldest hominid DNA recovered is about 100,000 years old, so comparisons of ancient fossils relies on morphological characteristics. 

What is noticed is when looking at fossils from oldest to youngest is that each successive generation of fossil has more human-like features, and less ape-like features including:

  • Less Tree Climbing
  • More upright posture
  • Mouth and jaw changes
  • Carnivorous/omnivorous teeth
  • Mastery of Fire (signs found near some fossils)
  • Mastery of Tools, and successive tool improvements
  • Clothing (perhaps tools, as well as some artifacts with at least the Neanderthals)
  • Skull shape, and increased brain size
  • etc

And, I believe the morphological characteristics in the hominid ancestors progress forward in time towards the modern human.

Now it would be a misnomer to say that Humans evolved from the Chimp, but rather that there would be a common ancestor for both the modern humans and modern chimpanzees, and I believe the hominid/primate fossils are approaching that point, but haven't quite identified a single common ancestor.

Are all the hominids that we've discovered human ancestors?

It is believed that Homo Sapiens and Neanderthals lived side-by-side for thousands of years.  Perhaps also Homo Erectus.

There are two ways that species can evolve.  Either a "split" as happened between humans and chimpanzees, with each new species following a separate evolutionary path.  Or, perhaps an entire population could slowly change as one might see with a small, very aggressive male population, or perhaps a disease resistant gene.  Perhaps you could include genetic drift with physical isolation of populations.

As mentioned, Y-Chromosome Adam is younger than Mitochondrial Eve.  But, this might not be unexpected with a higher percentage and more evenly distributed population of women having children than men.  And in fact, with a tribal society, it may not be uncommon for a conquering tribe to maintain the female bloodline, but terminate (or dilute) the male bloodlines.

Now, the question is whether these splits were 100%, or if there was later mixing.  And, there are some indications that Homo Sapiens and Neanderthals did in fact interbreed.  It would be possible to specify an inheritance pattern in which neither the Neanderthal maternal mitochondria, nor the Neanderthal paternal Y chromosome are maintained, yet other hybrid genes are maintained. 

Note, gene inheritance is more than just splitting 23 pairs of chromosomes, but there are provisions for gene recombination, in which parts of chromosomes are mixed and given to the children.

Anyway, there appears to be a progressive development of the hominids towards humans as seen through the fossils.

But, likely some of the fossils represent developmental dead-ends, and are not direct human ancestors.  But, even the so-called dead-ends such as Neanderthals may have contributed some additional genetic material to the human genome.

http://en.wikipedia.org/wiki/Homo_(genus)
http://en.wikipedia.org/wiki/Timeline_of_human_evolution
http://en.wikipedia.org/wiki/Human_evolution#History_of_ideas
 

Offline hamza

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Re: How do we trace human evolution?
« Reply #2 on: 03/07/2011 20:58:05 »
Wowww. CliffordK. Thanks alot for lending me so much of your time(obviously) which i really appreciate. Now that was a lot of molecular genetics and some other stuff that I couldnt comprehend completely, forgive my naivety. I wish I could talk to you in person so you could enlighten me with your knowlede, which u clearly have in abundance about evolution. One thing that i am  still failing to grasp is the fact of "descent". I think i should return to the very basics and start by asking, What makes us imply that someone has actually descended from some preceding organism. for example if I take myself as an object then what would prove me coming from my parents would be the fact of birth. After that comes genetics which would actually show 100 percent predicted genome when compared to my parent's.
                             And applying this to the million years old human fossils, what proves that that human fossil could be a descendent of an even million years old hominid fossil when neither the fact of birth can be recorded nor the fact of 100 percent similar genetics. Please forgive me for my erroneous analogies as I have clearly not a very good understanding of evolution but thats the whlole point why I am asking and want to know.
 

Offline grizelda

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Re: How do we trace human evolution?
« Reply #3 on: 05/07/2011 10:19:18 »
I was reading about marine worms called Osedax which live on the bones of whales which have died and fallen to the seabed. They have been traced back 30 or 40 million years and possibly much earlier. The Osedax larva are not male or female, but when they land on a whale bone they become female, and soon cover the bone like a shag carpet. Later arriving larva land on the females and become dwarf males, living in the female, sometimes hundreds of them, for their entire life. So, if we were evolved from this ancient species, I would assume we would carry some pattern in our DNA which carries the memory of the tens or hundreds of millions of years males spent living in the females body. I'm just speculating at this particular chain of being of course, but it is likely that, when the complete DNA of all the species we can access has been recovered, along with the behaviors we can observe, that future supercomputers will data-mine this database to give us a fairly accurate history of where we came from and where we got the behaviors we exhibit.

 
 

Offline CliffordK

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Re: How do we trace human evolution?
« Reply #4 on: 07/07/2011 02:42:18 »
Hello Hamza,

I must admit that I'm not a geneticist, but more of a generalist...  but I do try to consolidate information.  The internet is a wonderful tool for finding information and augmenting details.  You will undoubtedly encounter many very intelligent instructors in genetics, archeology, and anthropology at universities around the world as long as they are not overly burdened with religious dogma.

As far as you being 50% your father, and 50% your mother.

There are spontaneous cellular mutations.

There is a mutation rate of about 1 / 10,000,000,000 (1 in 1010).
You have about 6,000,000,000 "base pairs" in your genome (6x109).
And, about  (10,000,000,000,000 cells) (1013)

With all the replication error repair mechanisms, this is an extraordinarily low error rate, but still not insignificant.

So, really, you should think of yourself as receiving 49.999999995% your father's genes, and 49.999999995% of your mother's genes, and having about 0.00000001% NEW genes. 

While you may have actually received a full compliment of your parent's genes, it is quite likely that someone in your close family didn't.

You will likely also have many different minor mutations in the cells in your own body.

Some of the mutations are lethal on the cellular or organism level.  Some are passed on, or perhaps even selected for in a community (which would then mean evolution).
 

Offline hamza

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Re: How do we trace human evolution?
« Reply #5 on: 07/07/2011 21:56:03 »
Still hard to grasp, but , is genetic measurements the only reliable tool to conclude the descent of an organism from a parent. What is the one single point of surety that makes it impossible to say someone is our parent or child viceversa
 

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Re: How do we trace human evolution?
« Reply #5 on: 07/07/2011 21:56:03 »

 

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