Understanding Evolution: The Question Thread
Post Reply
 
Thread Rating:
  • 1 Votes - 5 Average
  • 1
  • 2
  • 3
  • 4
  • 5
11-10-2012, 01:23 AM
Understanding Evolution: The Question Thread
So as far as science goes, I'm a physics guy. That's about it. I like applying math formulas to real life scenarios and getting accurate predictions like I can see into the future (I predict that the ball will land exactly 3.7 feet from the launch point. Ta-da!) But as far as biology goes (and chemistry), I've never been a fan.

So I constantly have questions about evolution and natural selection, as I'm sure most of you do as well. So let's combine them all to this thread. I figure it will be useful for the theists who only know evolution from the religious vantage (i.e. incorrectly).

I'll start off with a question I sometimes wonder.

If all species are a result of their own journey through the random helpful mutation game, why do so many species have essentially the same face setup?

Basically, tons of us came out of billions of years of mutation with two eyes toward the top, on the same side of the head. A nose directly below the eyes, generally with two nostrils. And a mouth below that, with a jaw and two rows of teeth. A realize there are lots of exceptions, mostly insects. But there are a TON that fit this description. Why are we all so similar? Is this the most efficient setup for survival?

To me, this is like asking a 1,000 people to draw anything they can think of and 700 of them all draw a giraffe.

"Ain't got no last words to say, yellow streak right up my spine. The gun in my mouth was real and the taste blew my mind."

"We see you cry. We turn your head. Then we slap your face. We see you try. We see you fail. Some things never change."
Find all posts by this user
Like Post Quote this message in a reply
[+] 1 user Likes Buddy Christ's post
11-10-2012, 02:01 AM
RE: Understanding Evolution: The Question Thread
A common selection pressure faced by the relevant species will lead to the same traits. This is known as convergent evolution. One good example is the placental mammals and the marsupials.

Here's my hypothesis on the face setup positions:
1) The eye is usually located at the top part of the face to provide a wider field of vision. A wider field of vision allows better detection of predators or prey, so as to take action as soon as possible.

2) The nose is usually located above the mouth to aid scent detection while eating. Detecting that something to be consumed is dangerous early helps in survival. The reason we have two nostrils? Probably as a backup if one fails such that breathing can continue. One interesting thing about nostrils is that quite a large proportion of humans only breathe through one nostril at a time (not sure whether this applies to animals).

3) The mouth is usually located below the face, such that when consuming something, the other sensory organs will not be affected (for instance: infections).

Hope that helps Smile

Welcome to science. You're gonna like it here - Phil Plait

Have you ever tried taking a comfort blanket away from a small child? - DLJ
Find all posts by this user
Like Post Quote this message in a reply
11-10-2012, 04:21 AM
RE: Understanding Evolution: The Question Thread
(11-10-2012 01:23 AM)Buddy Christ Wrote:  To me, this is like asking a 1,000 people to draw anything they can think of and 700 of them all draw a giraffe.

Think common ancestry. They did not all "draw anything". It's like they were given a template to draw from. There are advantages for bilateral symmetry, (physics of swimming), food is in front of you, danger on top of you, (in the water), waste out the back. But jellyfish are not bilaterally symmetrical, (I think). So it's not the only way to evolutionary success. Here's a Physics link for an explanation for advantages of bilateral symmetry :
http://www.biology-direct.com/content/pd...0-7-22.pdf

Insufferable know-it-all.Einstein Certified Ancient Astronaut Theorist and Levitating yogi, CAAT-LY.
Yeah, for verily I say unto thee, and this we know : Jebus no likey that which doth tickle thee unto thy nether regions.

Find all posts by this user
Like Post Quote this message in a reply
[+] 1 user Likes Bucky Ball's post
11-10-2012, 09:06 AM (This post was last modified: 11-10-2012 09:12 AM by PoolBoyG.)
RE: Understanding Evolution: The Question Thread
1. Evolution is modification, not reconstruction. Many of the species today stem from ancestral species who had a basic structure. To have a radically different structure just isn't how evolution works. The mouth isn't just going to "drift" above the eyes, or end up in the feet. Modification works within the limitations of the existing structure. Although, in some aquatic mammals, the nostrils drifted above the eyes and onto the top of the head.

2. The main topic here seems to be convergent evolution.
"Eyes", for example, have independently developed in many species, and always on a "head", and always in pairs. There does seem to be evidence that certain structures are more beneficial (on certain earth environments anyway).
Find all posts by this user
Like Post Quote this message in a reply
11-10-2012, 10:51 AM (This post was last modified: 11-10-2012 11:01 AM by ghostexorcist.)
RE: Understanding Evolution: The Question Thread
Quite simply, these features arose in the oceans where life first began. Humans can trace their lineage to the fish who first stepped fin on land some 400 million years ago. If you look at fish, they have simpler versions of our physical features: two eyes above a mouth, symmetrical body layout, 4 limbs, etc. (Take a deep breath.) The fish gave rise to amphibians, who gave rise to reptiles, who gave rise to mammals, who gave rise to primates, who gave rise to humans. All of us have the same basic layout because of our aquatic common ancestor. Primates, wolves, and big cats have eyes that are set forward because we are predators. This gives us a better view of our world, and overlapping visual fields gives us a better since of depth, allowing us to reach out and grab our prey. Many types of non-predator animals have their eyes set on the sides of their heads and not the front.
Visit this user's website Find all posts by this user
Like Post Quote this message in a reply
[+] 1 user Likes ghostexorcist's post
11-10-2012, 11:11 AM
RE: Understanding Evolution: The Question Thread
Here is a question for you guys. If related animals with different chromosome numbers produce sterile children, how is it that the human lineage propagated after the fusion of our Chromosome #2 (giving us 46 instead of 48)? Carl Zimmer directed me to a paper that answers this question. I'm just interested in how you guys might answer it.
Visit this user's website Find all posts by this user
Like Post Quote this message in a reply
11-10-2012, 11:15 AM
RE: Understanding Evolution: The Question Thread
Not all breeding of closely-related species results in sterility. Some breeding of horses and mules produce donkeys that are capable of reproducing. It isn't as common but it need only happen a few times.

Evolve
Find all posts by this user
Like Post Quote this message in a reply
11-10-2012, 11:21 AM
RE: Understanding Evolution: The Question Thread
This doesn't answer your specific question, Buddy, but I wanted to share that I've just started listening to lectures on Evolution class from Open Yale Courses. It's a great way for someone like me who has a ZERO background in evolution to pick up a basic college level understanding of the topic.

Here's the link if anyone's interested. http://oyc.yale.edu/ecology-and-evolutionary-biology

And by the by...Yale has a buttload of lectures on lots of topics available through iTunes U. Thumbsup


EDIT: This one line corrected a major flaw in the way I thought I understood evolution:

"Natural selection is not "survival of the fittest," but rather "reproduction of the fittest.""

"All that is necessary for the triumph of Calvinism is that good Atheists do nothing." ~Eric Oh My
Find all posts by this user
Like Post Quote this message in a reply
[+] 2 users Like Erxomai's post
11-10-2012, 11:33 AM
RE: Understanding Evolution: The Question Thread
(11-10-2012 01:23 AM)Buddy Christ Wrote:  If all species are a result of their own journey through the random helpful mutation game, why do so many species have essentially the same face setup?

To start with, your initial premise is wrong. It's not random. Natural selection is never random. If a new trait helps the individual survive better in its environment AND is able to be passed on genetically to its offspring, then that trait is selected into the genetic line. If it's harmful to the creature, then that trait is selected out of the genetic line.

(11-10-2012 01:23 AM)Buddy Christ Wrote:  Basically, tons of us came out of billions of years of mutation with two eyes toward the top, on the same side of the head. A nose directly below the eyes, generally with two nostrils. And a mouth below that, with a jaw and two rows of teeth. A realize there are lots of exceptions, mostly insects. But there are a TON that fit this description. Why are we all so similar? Is this the most efficient setup for survival?

To me, this is like asking a 1,000 people to draw anything they can think of and 700 of them all draw a giraffe.

I'll take a stab at it. This is just what percolates up to the top of my head.

Eyes:
Eyes higher up can see farther. Putting eyes on our chin means we don't see as far. For example, hiding in the grass, all we could see is grass unless we lift our whole head out of the grass (if our eyes were on our chin). Having them higher up means we only lift the top portion of our head out of the grass. Sticking too much of our head out of the grass means we are more visible to our prey or predators - remaining concealed is a huge evolutionary advantage.

Eyes too close to the mouth would get in the way while eating - wouldn't want to get poked in the eye while trying to eat a leaf off of a twig. Most animals have elongated jaws with their eyes not only above the mouth but behind it as well, keeping the eyes safe while the animal eats. Almost the only exception are animals that eat with their hands, such as primates - with meals that result from hand-eye coordination, it's less necessary to have distance between the mouth and the eyes.

Eyes in the front give binocular vision. Without that, you cannot judge distance to your prey. All predators have frontal eyes because knowing the exact distance to their prey is vitally important to getting a meal. Herbivores that don't need distance vision but who do need to be able to see to the sides and behind them to watch for predators have eyes farther out to the sides of their heads (deer, rabbits, mice, etc.) which gives them much better peripheral vision, including up (for flying predators) and backward (for predators behind them).

Nose:
The nose serves two main purposes, smelling and breathing.
Smelling: Two nostrils helps with binocular smelling (yes, I know that's not the right word but I don't know what a bi-olfactory word would be). In short, if the smell is stronger in our right nostril, we turn right to find the source. For creatures that have better olfactory reception than humans (just about everything on the planet), scent is vitally important to survival, to recognizing friend from foe from danger, to finding meals, etc. The nose is in front because, unlike vision, every inch counts. Smells diffuse in the air very quickly. A tasty piece of meat smells great when your nose is one inch away, is barely noticeable when your nose is a few feet away. For scent, proximity is extremely important, so the nose is at the front of our face. It's also right below the eyes because animals turn their head to follow scent, and their eyes help them find the source visually - the two senses are somewhat linked, at least when trying to find that yummy smelling meal.

Breathing: While we eat or drink, we can't breath. For many predators, killing the prey means latching on with teeth and holding on for quite some time. This means using the nose to breathe. So the nose needs to be near the windpipe and connected through the same throat that the mouth uses for breathing. We also need to inhale to draw scent into the nose, so air-flow is required for that too. If the nose were below the mouth, then every time we eat or drink we could get blood or other fluids, even food, into the sinus airway - not good. So the nose is above the mouth but still really close to it to share the same throat, but still not above the eyes for reasons mentioned above.

Mouth:
A jaw that opens and closes on a hinge is required for chewing. So the fact that all higher orders of animals have a jaw is not surprising - we all gotta eat. Higher orders (stuff that isn't an insect, basically) need lots of nutrition to maintain our complex selves, so lots of eating. Stomachs and intestines do the digesting, but we need to get big bits of food into the digestive tract - food that is often too big to swallow without ripping, chewing, and grinding it up first. Except for snakes who found another way. Two rows of teeth, one on top and one on the jaw is just as obvious - teeth do the biting, ripping, chewing, and grinding. We need something hard there, a soft palate and tongue just won't do much to reduce food to digestible chunks. So teeth it is.

Now, I'm sure at some point other things were tried by evolution. Look at how a fly eats, by barfing acid onto its food to sort of pre-digest it into a paste, then sucking up the paste. No teeth required. And it works for them.

So why doesn't everything eat like a fly?

Common ancestry. At some point, we had an ancestor that had these characteristics. Probably a fish. Maybe some of her contemporaries had other characteristics, like maybe some fish in the same ocean barfed on its food (doubtful, but funny to think about - in truth, she was probably very much like all the other fish, only slightly, marginally, almost imperceptibly better). But our ancestor was very successful and bred well and passed these traits on to billions of generations since.

While other features have diverged, like thumbs, fur, scales, wings, and a bunch of other differences, these eyes, noses, and mouths were universally successful. Even they have evolved differently, like a snake's unhingeable jaw or a dog's amazing sense of smell or an eagle's incredible eyesight, but the basics of what we use them for and why they are located where they are, have remained mostly the same for hundreds of millions of years.

Except for Egyptians - apparently they all had two eyes on the same side of their face.

"Whores perform the same function as priests, but far more thoroughly." - Robert A. Heinlein
Find all posts by this user
Like Post Quote this message in a reply
11-10-2012, 11:39 AM
RE: Understanding Evolution: The Question Thread
(11-10-2012 11:15 AM)TheBeardedDude Wrote:  Not all breeding of closely-related species results in sterility. Some breeding of horses and mules produce donkeys that are capable of reproducing. It isn't as common but it need only happen a few times.

I raised a similar point in this brief essay I wrote on whether Humanzees were possible.
Visit this user's website Find all posts by this user
Like Post Quote this message in a reply
Post Reply
Forum Jump: