The human body is amazing. But there seems to be some evolutionary changes that appear to not make sense regarding redundancy.   While not necessarily the primary reason for their existence, the human body has a great deal of redundancy.    Two eyes.  Two arms. Two legs Two ears Two nostrils Two lungs Two kidneys Two sets of teeth A very large liver that can work in part. Two brain hemispheres that can (to some degree) do the work of the other. An appendix that is not critical.   But why do we not have two hearts? It would seem like a good idea to have two smaller hearts, together they work above optimally, but survival would be possible with one.
90757
We have two eyes, but we don't have two hearts. Why do humans have two of some organs, but not all?
121787
As a student of biology when ever I come by artificial cloning, I always find examples of females being cloned - Dolly the sheep, CopyCat, Daisy, etc. The only male I could see was Fibro mouse and a few more. What is the reason behind this? Is the male genome more difficult to be cloned? I am specifically looking for genetic reasons or other complications.
83433
Although farmers appear to be able to tell their cows apart, cows look very much alike to me. And this similarity in appearance seems to be a general trait across the animal kingdom: one individual of one animal species looks much like another.  Why do human facial and body shapes vary so much?  I understand that human beings live in many different environments (e.g. hot and cold) and have adapted to these (e.g. through lighter or darker skin color), but there seems to be much variation that has no apparent evolutionary purpose. So does the difference have a purpose in itself? That is, did we evlove to vary in appearance, and what is the purpose of this variation?
45681
It may be useful in sculpting and character design for example for the body parts (head, eyes ...)
14279
Why does evolution not make life longer for humans or any other species?  Wouldn't evolution favour a long life?
68511
In order to build an intelligent design such as a bridge or a mechanical watch, you need a series of non useful steps.  As far as I understand, in random evolution theory, the "intelligence" involved is the process of natural selection.  The problem with this is that natural selection requires that each step be advantageous right away. If I want to build a bridge, I need many steps which would be disadvantageous until the final product which would be advantageous. This would be like trying to write a computer program where each line of code must be advantageous to the program. An intelligent design just cannot be done like this.  How does modern biology deal with this problem? To say it all happened at once, is not possible since the probabilities against this are simply outside the capabilities of a random system. Furthermore even if by some freak monumental event it happened, it would need to happen again many times since there is a huge diversity of intelligent designs in life forms such as lungs in birds vs gills in fish, or sexless reproduction in bacteria versus male/female reproduction in animals (which are fundamentally different).  (Also, as side question has there been ANY experiment demonstrating that such a thing is even possible? I mean for example, to have a computer simulation of random self-replicating molecules, then having an intelligent human being picking out the best version and eliminating the others, then repeating, etc. until you have an intelligent design.)
20681
I was thinking about something the other day (that is probably stupid), and thought this would be a good place to talk about it.  If someone wanted to draw its family tree over the last 1000 years, he'd write a binary tree with a depth of about 40 (counting 25 years on average between each generations). This tree would have 240 leaves, or about 1012 ancestors on the deeper level. That is obviously much more than the total world population and a stupid figure when you think about it.  The only explanation that I can think of is that a real genealogy tree must have "linked" branches at several levels that change the actual number of ancestors. Anyway, for an average person, how many ancestors would that make? Could one assume that all or nearly all of the persons that lived in its country or world region a 1000 years ago would be part of its ancestors?
113457
If a hermaphrodite animal (like slug, snail, etc) finds a partner they can mate immediately.  If another animal with "normal" reproduction (lets say a mouse) finds a partner they can only mate if they are opposite genders.  So it seems logical that the hermaphrodite way of reproduction is more successful than the "normal" way.  But it is not, as far as I know all higher developed species are using, the standard way of reproduction (male and female).  Why? What are the disadvantages of hermaphroditism?
32549
Ok, this is a bit of a tangent question, but it came up yesterday and I didn't know the answer:  How are arms and legs defined physiologically? For example, we say humans have two arms and two legs, while cats have four legs, and some monkeys (appear) to have four arms (although I guess they could be legs too). It's really unclear to me how we make these distinctions.   So:  What is the physiological definition of both "arm" and "leg"? How are they different?
55228
So, it is established that using the bodily fluids of a zombie hides you from zombies. The characters know this. (They also may know that keeping semi-disabled zombies also works).  Why don't they just keep the innards around to keep themselves safe?
89966
I read a story this week on Richard Lenski who has been 'evolving' E. coli for more than 50,000 generations now.  One comment I read was from someone who doesn't accept Evolution who pointed out that we haven't seen a single celled organism 'evolve' into a multi-celled organism.  Another person responded and said that a bacteria is not going to evolve into something that isn't a bacteria.  So, if Evolution created single celled organisms and then multi-celled organisms how might that change have happened?  And is it possible to recreate that set of driving forces to make a bacteria something other than a bacteria?  To that end, what advantage does being multi-cellular have over being unicellular (if that's even a word)?
18636
Does someone know why DNA is composed of four nucleobases? In particular, is there an explanation for the number? Why four and not two, or eight?
73494
Given that the mechanism of natural selection is sensitive, how do species survive in an evolutionary midway? The ability to breath in air requires complex protein systems. An animal that is developing these organs would not be able to utilize its function until it fully evolves. While it doesn't, wouldn't the wasted resources used in growing half-developed lungs be.. wasted? Or is all evolution continuous?
105698
I made an answer on the Scifi.SE that can be read . It is about how the characters in the story Jurassic Park might have gotten DNA for all the species shown.  In my answer, I said this:     Apes and Humans, for example, share over 99% of their genes. That means the difference between our species is less than 1% of our genes. In fact, all life on Earth shares about 50% of it's genes.   but in the original posting (before someone edited it) I chose to use the word DNA instead of genes.  He left this comment in the section to explain the edit:     Sorry, I'm a biologist, I can't help it. Humans and apes share 99% similarity in the coding sequences of their DNA, the ~5% that codes for genes, not on all the DNA. I simplified this to genes for the answer.   I have a basic high school understanding of DNA and genes, so I'm afraid I fail to see the difference between using "DNA" or using "genes" in my statement. I understand that genes are specific sequences of DNA that are used by the cell in some way. I understand that DNA is more generic, including all of the strands, whether they are used or not, whether they seem to code for something or not.  So is it wrong then to say that apes and humans share 99% of their DNA or is it equally correct to say "genes"?
82798
What is the basis for believing that there is such a thing as human rights? I am all for human rights but it could be argued that the notion of human rights is imaginary and reducible to absurdity (that humans by virtue of being born are magically entitled to certain things) when trying to prove it scientifically or logically.   It also seems incompatible with evolution, where survival of the fittest would dictate, that you either have what it takes to secure the resources necessary to survive, or you perish if unable to secure said resources. Evolution doesn't state anywhere that everyone is born with a right to a specific allotment of resources. Is it possible to reconcile these contradicting positions or is it more logical to conclude that human rights are a human invention?
124073
It's something that's always bothered me. Especially now I'm watching The Walking Dead series. People die and turn into Zombies, from The Walking Dead we see that only part of the brain becomes active. Do they actually have a working digestive system and requirement for food or is it just impulse? If it's impulse... why?
70799
I read that wherever there is polytomy there is an unresolved pattern of divergence. I don't understand why this is so.  When divergence takes place, is it necessary that there will be division into only 2 paths? Can't there be more than 2 paths with all the paths being equally related to each other (that is, no 2 paths being related more to each other than to a third path)?  In other words, does a fully-resolved phylogenetic tree have to be dichotomous?