Sunday, June 12, 2011

monkey to man [in a nutshell]

This a common question I have encountered from time to time while discussing evolution and religion with different people, and when asked it I always feel that the person asking the question asks it as if it is a brick wall and there is nothing I will be able to say to clear the question up. Maybe you yourself have even asked the question or pondered it with in your own mind... so to cut to the chase that all important question that I will attempt to answer here, in a not to lengthy explanation is;

And if you are not overly familiar with human evolution or are a strong believer in religion that can seem like a very powerful question to postulate to an athiest/evolutionist/rational individual, but it is a very easy misconception to clear up.

Q: If we came from monkeys, why are there still monkeys?

The Answer:

First off the correct answer is, we actually did not evolve from monkeys, if you trace back our evolutionary origins we actually stem from the Ape clade. (im not going to spend the time to explain the difference between monkeys and apes other than that monkeys have tails and apes do not)

Ok so we know we did not evolve from monkeys but we did evolve from apes, so if we evolved from apes why are there still apes? Well for one there is not just one species of ape as there is not just one species of monkey, this is already slightly good information allowing us to root the human species with in the ape clade as an evolved species of ape. below is a graphic depicting very basically the evolutionary radiation with in the ape clade. which I will further explain below;


The figure above is what is known as a cladogram also referred to as an evolutionary tree. This tree diagrams the evolutionary history leading to all the extant (living) species of apes. The tree is rooted in deep geologic time on the scale of millions of years, also if you follow the tree you will see that it always branches at the circular nodes. These nodes are key to explaining the reason that if we evolved from apes why are there still apes. These nodes represent what is known as a most common recent ancestor (MCRA).

A MCRA is a species that two separate species both share, the same way two cousins both share a set of grandparents. Over time the grandparents will pass away but both of the lineages will continue one, this is exactly what happened with the evolution of humans.  You can see that the node directly below humans branches both to us and off to branch once more with both Chimpanzees and Bonobos and is rooted in geologic time around 6 million years ago (mya). All of us being cousin species. Bonobos and chimps are more closely related to each other then to us but because of the presence of a MCRA located around 3mya we are both more closely related to each other then to any other branch of the great ape clade.  Thusly this means that our group as a whole (humans, chimps and bonobos) are all cousins to gorillas since both of our groups share a MCRA which existed around 8 mya, and so on with orangutans being the oldest of all the great apes, having split from out lineage some where around 13 mya.

ok even after reading this you may say, well yea that sounds good and all but how can you prove this to actually be true and not just a bunch of made up babble. Well we can prove this to be true first by basic homologies found though out the species such has the ability or even preference (in humans) to walk up right on two legs the the normal bi-pedal knuckle walking found in most other apes, as well as the main physical clincher, the opposable thumbs which stems from our history of living and moving though the trees. As well as the overwhelming similarities found at the skeletal level best shown in Huxley's 'Evidence for Mans Place in Nature';


  All of this, by this point, should be more than enough information to help you or the individual who has raised this question to you understand the full scale of how naive and foolish his or her question truly was, but now they are more knowledgeable and a better person because of it. Every now and then though you will run into one of those hard headed 'god did it' people who will not accept anything you say as true and there is nothing you can really do, but I will offer onc more, and the most compelling, piece of evidence for the case of Homo sapiens evolving from a MCRA shared by chimps. for this part of our explanation we must turn to GENETICS!


As we know genetics and DNA do not lie! so what could this evidence be that is the true nail in to coffin so to speak to this over used creationist question. Well if you look back up towards the top at the picture of the evolutionary tree you can see that it says that all species of ape posses 48 chromosomes or 24 pairs, except for humans who for some reason only posses 46 chromosomes or 23 pairs. Some will say 'HA! see they are different, and we could not be related to Chimps, apes or monkeys!' but here is where you are wrong.

When we look at the chromosomes of both chimp and human they look almost identical


Chimp chromosome map
Human Chromosome map
    

This might not mean a lot if you have never taken much in the field of genetics, but why do humans have only 23 pairs (excluding X and Y) and all other apes have 24 pairs? This answer was finally figured out when we learned about what is known as a dicentric chromosome (or a chromosome that has two centers or centromeres). This may happen by a mutation that would look something like this



Allowing for the Chromosome to have to separate centromeres and still be viable during both meiosis and mitosis (find out more here). When further studied chromosome 2 looked exactly like two seperate chromosomes found with in the chimps, and other apes, chromosomal map.

To sum this all up based on the evidence (which there is plenty more, most stooped in technical jargon) humans and apes both share a MCRA which gave rise to both lineages roughly 6 mya, one lineage went on to split once more giving rise to the now extant species of Bonobos and Chimpanzees (our closest cousin) while the other lineage during its evolution (human evolution will be its own separate entry) underwent a mutation linking two of its chromosomes together to form our present day chromosome 2 which was beneficial enough to the species that it was engrained into our genetics to keep the mutation eventually leading the evolution of the species Homo sapiens.

So the next time someone asks you, "If we came from monkeys, why are there still monkeys?" make sure they have a few moments to sit down and listen to the evidence. 

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sources

http://pandasthumb.org/archives/2009/02/the-rise-of-hum.html

Sullivan BA, DJ Wolff, and S Schwartz (1994). Analysis of centromeric activity in Robertsonian translocations: implications for a functional         acrocentric hierarchy. Chromosoma 103(7):459-67

http://en.wikipedia.org/wiki/Chromosome_2_(human)











(Human Chromosome Map)

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