What is Evolution: Definition and 731 Discussions

Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes that are passed on from parent to offspring during reproduction. Different characteristics tend to exist within any given population as a result of mutation, genetic recombination and other sources of genetic variation. Evolution occurs when evolutionary processes such as natural selection (including sexual selection) and genetic drift act on this variation, resulting in certain characteristics becoming more common or rare within a population. It is this process of evolution that has given rise to biodiversity at every level of biological organisation, including the levels of species, individual organisms and molecules.The scientific theory of evolution by natural selection was conceived independently by Charles Darwin and Alfred Russel Wallace in the mid-19th century and was set out in detail in Darwin's book On the Origin of Species. Evolution by natural selection was first demonstrated by the observation that more offspring are often produced than can possibly survive. This is followed by three observable facts about living organisms: (1) traits vary among individuals with respect to their morphology, physiology and behaviour (phenotypic variation), (2) different traits confer different rates of survival and reproduction (differential fitness) and (3) traits can be passed from generation to generation (heritability of fitness). Thus, in successive generations members of a population are more likely to be replaced by the progenies of parents with favourable characteristics that have enabled them to survive and reproduce in their respective environments. In the early 20th century, other competing ideas of evolution such as mutationism and orthogenesis were refuted as the modern synthesis reconciled Darwinian evolution with classical genetics, which established adaptive evolution as being caused by natural selection acting on Mendelian genetic variation.All life on Earth shares a last universal common ancestor (LUCA) that lived approximately 3.5–3.8 billion years ago. The fossil record includes a progression from early biogenic graphite, to microbial mat fossils, to fossilised multicellular organisms. Existing patterns of biodiversity have been shaped by repeated formations of new species (speciation), changes within species (anagenesis) and loss of species (extinction) throughout the evolutionary history of life on Earth. Morphological and biochemical traits are more similar among species that share a more recent common ancestor, and can be used to reconstruct phylogenetic trees.Evolutionary biologists have continued to study various aspects of evolution by forming and testing hypotheses as well as constructing theories based on evidence from the field or laboratory and on data generated by the methods of mathematical and theoretical biology. Their discoveries have influenced not just the development of biology but numerous other scientific and industrial fields, including agriculture, medicine and computer science.

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  1. W

    Time evolution with time dependent Hamiltonians

    I understand that in general, it's not true that in the case of a time dependent hamiltonian, the exponential map of the Hamiltonian is not a unitary transformation/the time evolution operator? U(t) \ne e^{-i \frac{H(t)}{\hbar} t} Is this thing allegedly not unitary or is it just not time...
  2. A

    Did our brains evolve to understand quantum mechanics?

    Lawrence Krauss says that We evolved as human beings a few million years ago on the Savanna in Africa and we evolved to escape tigers, or lions, or predators. You know, how to throw a rock or a spear or how to find a cave and we didn't evolve to understand quantum mechanics. How correct is the...
  3. C

    Time evolution of a quantum system

    Homework Statement Let the time evolution of a system be determined by the following Hamiltonian: $$\hat{H} = \gamma B \hat{L}_y$$ and let the system at t=0 be described by the wave function ##\psi(x,y,z) = D \exp(-r/a)x,## where ##r## is the distance from the origin in spherical polars. Find...
  4. S

    Cause of evolution of medicinal plants

    i wish to know why have plants with exactly required medicinal value has evolved. is there a some sort of lock and key like reason which helps to evolve medicinal plants for many disease? i also want to the logic behind using water and other solvent for extraction of solvents. some time...
  5. C

    Expectation value of the time evolution operator

    This problem pertains to the perturbative expansion of correlation functions in QFT. Homework Statement Show that \langle0|T\left[exp\left(i\int_{-t}^{t}dt' H_{I}^{'}(t')\right)\right]|0\rangle = \left(\langle0|T\left[exp\left(-i\int_{-t}^{t}dt'...
  6. R

    Cusps in the evolution of closed strings

    Homework Statement This is problem 7.7 in Zwiebach's book, 2ed ed. In (b) he want us to show that near the cusp, ##y\sim x^{2/3}.## In (d), Check that the period of the motion of the closed string is ##\sigma_1/4c##. How many cusps are formed during a period? Homework Equations (b)...
  7. C

    Can Astronomy and Cosmology Bridge the Gap Between Creationism and Evolution?

    Alright, I'll start off just saying, the title really isn't my question, but it is related. I was tasked with the job of creating/giving a presentation about creationism vs evolution. Of course it isn't supposed to be about the subject as a whole, but a specific topic within that broad subject...
  8. S

    Is Evolution Still Happening in Humans?

    I have a rudimentary understanding of evolution. Simply put it starts with chance and guided by natural selection which is not random. This is my understanding as of now not sure if its correct. In this video http://bigthink.com/videos/mankind-has-stopped-evolving-2 he says humans have stopped...
  9. jim mcnamara

    War, space, and the evolution of Old World complex societies

    http://www.pnas.org/content/early/2013/09/20/1308825110 War, space, and the evolution of Old World complex societies Peter Turchina, Thomas E. Currieb, Edward A. L. Turnerc, and Sergey Gavrilets Intense warfare as an explanatory model for driving the development of stable complex societies.
  10. lpetrich

    Eukaryote high-level evolution - have we succeeded in mapping it?

    The overall phylogeny of eukaryotes has long been a difficult and contentious subject, almost as bad as the phylogeny of prokaryotes. One could recognize some well-defined groups, but that was about it. But as biologists learned out to sequence proteins, and then nucleic acids, they got a...
  11. M

    Is Modern Human Evolution Still Progressing or Have Selective Pressures Changed?

    I couldn't really find anything about this via Google, so I thought I'd pop on down to my favorite place in the interwebz! So obviously evolution in early man was in an overall advantageous direction, but what about now, in modern man? Back then evolution in humans would have worked similarly...
  12. J

    Eigenstate to eigenstate evolution with no intermediate superposition?

    Eigenstates of some observable O are represented by orthonormal vectors in complex Hilbert space. Is it true that the only possible way that the state vector can evolve from one eigenstate of O to the next, is to rotate between the two eigenvectors so that intermediate state vectors are...
  13. J

    Eigenstate-to-eigenstate evolution with no intermediate superposition?

    Eigenstates of some observable O are represented by orthonormal vectors in complex Hilbert space. Is it true that the only possible way that the state vector can evolve from one eigenstate of O to the next, is to rotate between the two eigenvectors so that intermediate state vectors are...
  14. J

    Continuous evolution from 1 eigenstate of O to another O-eigenstate?

    Eigenvectors associated with distinct values of an observable are orthogonal, according to quantum mechanics. Does this entail that a quantum system cannot continuously evolve from one eigenstate into another, for ANY observable? At first, that seems strange: it seems like a particle...
  15. T

    On evolution of humans and that of other animals: any discrepancy?

    Question Summary: Do you think human evolution worked in the same way as other living things have evolved through natural selection? Don't you think the human evolution occurred faster than that of any other animals? And humans have possessed too many characteristics ( especially those of...
  16. N

    QM: Density matrix evolution

    Homework Statement Hi The density matrix evolves as \dot \rho = -\frac{i}{\hbar}[H,\rho] but is this equation written in the Schrödinger or Heisenberg picture? I'm not entirely sure how to figure this out. In my book it just mentions the equation, not how it is derived (which may have given...
  17. A

    Everything is not because of evolution

    Evolution answers most of the questions like - "Why are we social animals", "Why do we have nose, eyes etc". Because they were evolutionary advantageous. But I have seen this argument being used in wrong places. For eg: - In some book (sorry, I don't remember it now), the author said that we...
  18. Q

    Time evolution operator versus propagate

    I am trying to understand the how the time evolution operator is used versus the Feynman propagate. My limited understanding is the following for which I am seeking clarity: 1. The time evolution operator is a unitary operator which enables us to calculate a probability amplitude of one...
  19. J

    What is the goal of human evolution

    This might be a bit off topic, but I am curious about cycles of evolution. What is the goal of human evolution and how does the process happen in sync to the enviornment? My thoughts: Wouldnt the evolution goal be control? Meaning control by having the forces of the universe bend to you and...
  20. D

    Question about evolution - intermediate evolutionary traits

    Hi, I have question about what the current state of evolutionary biology has to say about how complex biological structures form. I'll just illustrate my question with an example, and I apologize in advance for using the incorrect terminology - I have very little biology training. For me it's...
  21. U

    TDSE, time evolution between states (Check my working please?)

    Homework Statement Hi guys, I've recently taken up quantum, so it's all very new to me, it would be greatly appreciated if someone could check my working!Let ψ1(x) and ψ2(x) be two orthonormal solutions of the TISE with corresponding energy eigenvalues E1 and E2. At time t = 0, the particle is...
  22. A

    Time Evolution of Measurables(Hamiltonian)

    Supposing a physical quantity f whose operator commutes with the Hamiltonian operator H, and supposing it has no explicit time dependence, then the result regarding the time derivative of the operators gives us that the quantity is conserved and its mean value does not change with time.The...
  23. H

    Neutron Spin Time Evolution in Interferometer

    Hey Everyone, I'm working on a question and can't quite get the answer out. QUESTION: Part (a) "\left|\alpha\right\rangle and \left|\beta\right\rangle are the eigenfunctions for neutrons polarized respectively along positive and negative z directions. If the neutron, initially in...
  24. E

    Help with electron evolution governed by Hamiltonian

    help with electron evolution governed by Hamiltonian ,,, Homework Statement an electron evolution governed by Hamiltonian H=(p^2) /2m +(1/(4Piε))* (e^2)/(r1-r2) give an energy approximation and what's the physical interpretation of the such a Hamiltonian Homework Equations The...
  25. S

    Animating Solar System Evolution from Real Physics Data

    I've recently been assigned a project by one of my professors to animate a solar system style disc using real data computed from a simulation of his, and I'm wondering what the best angle of approach for this project would be. I have some experience in Cinema4D animating things, and I'm...
  26. J

    Why things like relativity and evolution aren't called laws?

    I was reading in my textbook the definition of a scientific law: must be found experimentally valid over a wide range of observed phenomena. So why arent things like the theory of general relativity and the theory of evolution called the laws of evolution and the laws of relativity? Will that...
  27. O

    Sakurai page 181: Time evolution of ensembles

    From "Modern Quantum Mechanics, revised edition" by J. J. Sakurai, page 181. Equation (3.4.27), at some time t_0, the density operator is given by \rho(t_0) = \sum_i w_i \mid \alpha^{(i)} \rangle \langle \alpha^{(i)} \mid Equation (3.4.28), at a later time, the state ket changes from \mid...
  28. B

    Time evolution of density matrix

    Homework Statement Hi there. just working on a problem from sakurai's modern quantum mechanics. it is: A) Prove that the time evolution of the density operator ρ (in the Schrodinger picture) is given by ρ(t)=U(t,t_{0})ρ(t_{0})U^\dagger(t,t_{0}) B) Suppose that we have a pure ensemble at...
  29. R

    Time evolution of a particle in an ISW after the well

    Homework Statement How does the state of a particle in an ISW evolve with time after the width of the well doubles - from a to 2a If the particle starts in the ground state of the half width well, then immediately after the well doubles it will be undisturbed therefore the initial wave...
  30. J

    Energy of interacting particle and time evolution of p(x)

    In classical QM, using a photon to measure the location or momentum of an electron collapses the electron's wave function at the point of measurement, which then, over time, spreads out again (what I'll call "diffuses"). Fine. The question is: Does the energy of the measuring photon change the...
  31. J

    Is *All* of evolution propelled by natural selection?

    I've always thought that evolution was this mysterious property of the universe and that natural selection was almost a separate theory. Now that I look more into it, i can almost always rationalize an answer as to why a property of life is the way it is by natural selection. For example, i...
  32. A

    Does the E-coli Long Term Evolution Experiment Prove Evolution?

    I have read several posts asserting that mutation and natural selection cannot add complexity or useful functions to the genome. I'd like to add a link to an experiment that proves them wrong, and also teaches us a lot about how evolution works - the E-coli long term evolution experiment...
  33. L

    Time evolution of operators as projectors - confusion

    I have a confusion regarding expressing operators as projectors in Schrodinger and Heisenberg pictures. Please help. Consider a two-state system with |1> and |2> We know that e.g. a raising operator can be expressed as: \hat{\sigma}_+=|2><1| But here's my line of thought: In the...
  34. N

    My Misconceptions of Evolution

    According to Ryan_m_b it is a "misconception of evolution" that I could have been created at any time throughout the universe's existence, as opposed to just now. I'd be curious to learn why this is a "misconception of evolution" and why it is a fallacy of my logic to think otherwise. I expect a...
  35. Sab95

    Evolution of a star from a nebula

    I know that our solar system and sun evolved from a nebula of a giant star.. but what happened to the remaining of the star.. entire star cannot go boom.! at least some remaining portion of the primordial star should have existed in the form of a neutron star or a white dwarf. If it existed what...
  36. K

    Finding the time evolution of a state

    Homework Statement 1) Using energies and eigenstates that I've worked out, find time evolution ψ(t) of a state that has an initial condition ψ(0) = \begin{pmatrix} 1 \\ 0\\ \end{pmatrix} 2) Find the expectation values < Sy> and <Sz> as a function of time. Homework Equations...
  37. N

    Wavepacket Evolution: Questions on Time Evolution and Plane Waves

    I had a few questions regarding the time evolution of wavepackets of the form ∫ dk*A(k)*cos(kx-wt), where w = w(k) If the group velocity is zero, i.e; dw/dk evaluated at k' = 0, where k' the central wavenumber of the narrow packet, then do we essentially see complete constructive...
  38. 2

    High-heeled shoes and evolution theory.

    I always speculated that the reason why women wear high-heeled shoes (such as pumps and the like) is they give them an advantage (albeit a deceptive one) in attracting the taller male. There is enormous selection pressure being imposed on the height of our species, with our species getting...
  39. atomqwerty

    Can this be a Hamiltonian Evolution?

    Homework Statement Let be q(t)=e^{-t}\alpha and p(t)=e^{-t}\beta Can this be a Hamiltonian Evolution Homework Equations The Hamilton equations for \dot{p} and \dot{q}. The Attempt at a Solution Can be a Hamiltonian evolution if verifies Hamilton equations...
  40. C

    Possible different paths for evolution

    The question is not purely scientific but involves also huge amount of creative guess (which only shouldn't violate blatantly contemporary scientific knowledge). I think about something like "The future is wild" or some Dawkins' analyses of probability of evolution of different organs from "The...
  41. V

    What is the unit to use in evolution?

    And what are some good examples besides humans? I'm guessing that years don't matter as much as generational cycles. edit: for example, how many evolutionary cycles for humans would be contained in 100 years? Or dogs? Do you count by total age or reproductive age?
  42. J

    On the topic of evolution, are we distant cousins to, say, a blade of grass?

    Are we distant cousins to every single blade of grass and every single plant and animal on earth? Also, if all life on Earth had a single origin somewhere in the ocean, how did grass and plant life spread throughout the world so quickly?
  43. J

    The Evolution of Dogs: Domestication in a Short Time Period?

    I understand and completely accept the evidence for the former but i was just reading the greatest show on Earth and richard was saying how our domestic dogs are directly evolved from wolves, not foxes or anything else. If that's the case, wouldn't the lame argument "if we evolved from chimps...
  44. C

    Evolution of Physics: Could Physical Laws Change Over Time?

    What if physics laws are also evolving and changing with time? Like we have evolution in living species, may be we have evolution also in physics laws. (Better one lives, worser one dies) After all, in scientifically speaking, why we have that certain values for physical constants than...
  45. C

    Commutative free particle time evolution

    Homework Statement http://img853.imageshack.us/img853/2532/70224197.png Homework Equations i know schrödingher eq. and basic quantum formula The Attempt at a Solution i showed that the equality at the first question but i can not start from (a) part. how and where am i supposed to start...
  46. Drakkith

    Louisiana Schools Teaching Creationism Vs Evolution

    Apparently a few schools in Louisiana, which are private but have state funding, are teaching Creationism vs Evolution as competing theories. http://www.buzzfeed.com/andrewkaczynski/here-is-what-louisiana-schoolchildren-learn-about The article has a link to another one that explains that the...
  47. A

    I need a full proof of evolution ?

    Ok, i need a full proof of evolution to prove to someone doesn't accept evolution that evolution is true, someone that will never accept evolution even if he saw species evolving in front of his eyes!, but anyway i need a full proof of evolution with links of scientific researches and good...
  48. B

    Quasar Mass-Luminosity, High Mass Turnoff Evolution and a Synchronization Puzzle

    Quasar Mass-Luminosity High Mass Turnoff Evolution and a Synchronization Puzzle It is unusual that a generation of researchers has the opportunity to completely rewrite, to replace major established scientific theories. The observation that quasars are turning on and off, at a specific mass...
  49. E

    Is there any real scentisit (who is not creationism) reject evolution?

    Hello all, I was wondering if there is any modern real scientist (who is not creationism) rejects evolution based on purely scientific views? Because may be his religious beliefs obstruct his scientific view. I am interested in a highly credited person under this description. Thanks
  50. S

    What Are Some Common Questions and Misconceptions About Evolution?

    Hey guys I was in a discussion with my friend and I couldn't answers some questions about evolution .. and since I'm not that good in biology, I hope that I get some explained answers. Q1 : How can mutations produce organs ? Q2 : Do genetic mutations produce positive and negative changes ...
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