And a subclass of genetic drift is the Founder Effect, wherein a small population moving into a new environment (or otherwise cut off from its parent population such that gene flow has been eliminated) will have reduced genetic diversity. This will result in a population that can be quite distinctive from the parent population after a relatively short time, and is a major component of peripatric speciation.
This is probably pretty simplistic, but:
Cells mutate. If the right cell mutate (it has to be the germ cells, I think), the change in physiology will be passed down to the next generation. “Good” mutations help the organism survive and mate. If the organism can do those things better than its fellows, it will have more offspring.
Most mutations either have no discernible effect, or a minor one, or are deleterious to the organism. Usually, you’ll end up with a gene pool that has slight variations. This frog tolerates cold weather, this frog tolerates warm weather. It’s been a particularly hot summer, so the warm-loving frogs will leave more tadpoles. There will still be a few cold-lovers, and if there’s a cold year the warm-frogs will do poorly and the cold-frogs will thrive. If there’s a major environmental change- global warming wipes out winter- the genes for warmer and warmer temperatures will dominate, until your coldest-weather frog will still like warmer temperatures than its heat-loving ancestors.
This thread is past 100 posts and I’ve no idea what state it’s now in but I’m going to answer the OP literally, explaining evolution as far as I understand it without using any cite or source of any kind as I type this. I’m guessing at least one creationist poster has turned it into a trainwreck but i’m going to be sincere.
Evolution is the process whereby the characteristics of living organisms change over the course of multiple generations or the reproduction of the organism. As organisms reproduce, they change in slight ways which, over the course of time, accumulate into substantial changes, even resulting in the creation of entirely new species.
Evolution occurs primarily through mutations in the genetic code of an organism, a process which can happen in any number of ways; random change, exposure to chemicals, exposure to radiation, disease, and so on. While such mutations are random and most are irrelevant, those which happen to have a positive impact on the organism’s likelihood of successful reproduction will result in that mutation being more likely to be passed on to more organisms, a process commonly referred to as “natural selection.” Over time a sufficient number of such mutations can cause such substantial changes that the organism is so different from its ancestors that it constitutes a new species.
Species of organism do not necessarily evolve to become more complex or “better” organisms; any mutation that helps reproduction and survival will be selected for. However, the sheer scope and volume of living creatures in the world has resulted in a very great number of complex species evolving into existence.
I think that this is incorrect. It’s not the cells that mutate, it’s the genes that do.
That brings up an interesting question, though. Is the mutation carried in just one sperm (or egg), or all of them?
Evolution, in its broadest sense, is a change over time of the properties of a system based on previous properties of the system and on the external environment.
In a biological context, evolution refers to the changes in populations of living organisms based on the premises that, first, there will be some variation in traits of the population, second, that the traits of offspring will be significantly correlated to those of their parent or parents, and third, that some traits or combinations of traits will provide an organism with an advantage in the task of producing offspring. Those traits which lead to their carriers producing more offspring will gradually become more prevalent in the population of organisms, which can eventually result in extremely large changes.
Well, they both have the same number of particles.
Now excuse me, I’m leaving this thread for one less complicated.
Sorry I wasn’t more clear-the combining of information from different individuals was what I referred to as “random recombination” ie meiosis, followed by sexual reproduction.
Without trying to maintain any hijack of this thread, I was struck by the similarity of the above experiment to the initial cloning that produced Dolly the sheep. To simplify greatly, a cell whose nucleus was removed (and is therefore incapable of reproduction and arguably irredeemably damaged) was injected with a nucleus from a separate cell (also incapable of sustaining itself or reproducing). Through the application of electricity, both of these essentially nonviable components were stimulated to produce a cell capable of reproduction and differentiation, which I would argue basically is doing what is discussed in the quote above.
Rumor has it that this thread got hijacked, but I am playing along with the rules in the OP, so I haven’t read the thread yet.
Evolution is the process by which species change over generations, sometimes branching off into different species. The main driver for evolution is natural selection. Genes combine differently, and sometimes mutate. Natural selection occurs when the new combinations/mutations cause the animal with the new genes to be more or less successful at reproducing. If the new genes are harmful, then the new genes will likely die off. If the new genes are helpful, they will likely propagate over time, either replacing the old genes, or creating two different types if both the new genes and old genes have a niche.
Ah yes. Sorry I missed that.
Evolution is the inevitable process resulting when you have variable inheritance, and something that causes some variants of whatever type of inheritance is involved ( genes in Earth biology, of course ) to reproduce better. Natural selection, sexual selection, some guy trying to breed a better herd dog; it’s all evolution, just with different selection criteria.
I would also call what happens to many forms of information and ideas evolution; some spread and reproduce - in human minds, or human records - because they appeal better to human instincts or a human culture; others don’t appeal to or interest us, don’t reproduce and therefore languish or die out. This is closer to Lamarkian evolution than the Darwinian style Earth biology uses though.
Darwinian evolution refers to the type of evolution seen in the biology of Earth. Different genes are reproduced with greater or lesser frequency due to how they affect their host creature, and the ones that do so in a way that increases their chance of reproduction spread more. There is no foresight, no plan; only the end results of interactions with the environment ( which from a gene’s “point of view”, includes its host creature and other genes ). Being mindless, the genes are “selfish”; they are selected for according to what has benefited their reproduction and nothing else. While genes do cooperate, it is only because they have evolved such cooperation because it has in the past furthered their selfish replication.
The variation in genes that allows for such selection has several sources. Mutation being well known but actually minor. Genes imported from outside the species by retroviruses; something like 2 percent in humans IIRC. Recombination; where existing genes are reshuffled to produce a new combination of time tested genes; allowing variability without the outright randomness of mutation.
Evolution is a theory stating that organisms change to adapt to their environment. This happens by mutation, which introduces the changes, reproduction, which perpetuates them if adaptive, and attrition, which does not allow them to perpetuate if not adaptive.
Some people are pissed about evolution because they want to believe that
a. God created the universe in seven days or in 4004 BC or somesuch;
b. if we are the descendants of poo-throwing simians and/or share 90% of our DNA with flies, who eat poo, that somehow or another argues against the existence of a God.
A splinter group of “some people” believes in intelligent design, which is that evolution was shaped by God and, moreover, that this can be logically “proven.”
The end. Not.
There’s a certain “stable” set of alleles in play, as well as transient alleles due to mutation.
The alleles are propagated by individuals who survive long enough to pass said alleles along to their offspring, who then repeat the process.
Species are basically clusters of individuals sharing sets of core alleles and are linked by breeding relationships.
Evolution is the small changes that God causes so that organisms adapt to their environment without becoming new species.
Ooh, good answer.
The theory of natural selection was proposed by Charles Darwin, and presented to the public and the scientific community through his book “Origin of the Species”.
The process outlined by Darwin came in 3 steps:
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Overpopulation - A population of creatures grows larger than the environment can sustain.
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Variation - Within the population there are differences between individuals.
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Selection - Because the environment is overpopulated, members of the species compeete with one another for scarce resources, and the ones who are better suited (due to the traits described in step 2) survive to sire the next generation.
The survivors of this process posess traits which are better suited to surviving in the environment than the ones who died off, and pass these better traits on to their ofspring. When this process takes place repeatedly over millions of years (with some members of the population becoming isolated from one another), the accumulated changes can result in different groups of descendents of the original population no longer having enough in common to produce viable ofspring, and thus we have speciation.
A concern Darwin had, and which was pounced on immediately by his critics was the question of how small, accumulated changes could add up into some of the more complex structures observed in nature. While it makes obvious sense that an eye would confer a terrific advantage, this was clearly too complex a structure to just pop into being as a result of the normal variation between individuals. Further, the various steps towards getting a functional eye would include individuals who could not actually see, and would thus gain no survival advantage from the precursor trait. Eventually, scientists determined a set of steps wherein the precursor traits to the eye could provide a meaningful survival advantage (starting with a photosensitive set of cells on the surface, moving on to protecting that photosensitive area by recessing it, then shrinking the opening of the cavity for additional precision and focus, followed by a transparent covering for the cavity, followed by that covering developing into a lense, and eventually we have an eye).
During Darwin’s time, gene theory had not yet been developed, so the mechanism of inheritable traits that would vary between individuals was not yet understood. It was only significantly later that the discovery of DNA allowed scientists to pin the heritability concept as being due to this molecule.
With the development of gene theory, it became understood that the variation Darwin talked about in his second step was a result of mutations within the DNA. These mutations, if harmful, made an individual less likely to survive and reproduce, and thus the harmful mutations tended to die out. If the mutations proved beneficial, the individual was more likely to survive and reproduce, and thus beneficial mutations tended to spread.
Darwin’s concept of natural selection compeeted with the theory of Lamarkian evolution, which presumed that instead of just inherent traits, aquired traits could also be passed down from parent to child. This has largely gone out of vogue, though in certain traits, it is possible, for example the ability of mothers to pass on antibodies to their ofspring.
Sexual reproduction is a kind of meta-advantage in the constant war for surival, in that it serves to increase the ammount of variation between individuals in a sexually compatible population. As a result, such species “evolve” faster. This is particularly necessary in complex species since, due to the high number of genes, mutations that would have a major impact on a simpler creature (like an ameba) hardly impact a more complex species. A species that adapted to its environment too slowly would be at the mercy of changing environmental factors, and thus might die out entirely.
Artificial, rather than natural selection is a process whereby an intelligent designer such as humans, carefully controls the breeding of a species in order to produce a desired end result. One advantage of this form of slection is that the patron species can prevent a harmful intermediate step in the development of a beneficial trait from resulting in the extinction of the line before that trait can develop. Another advantage is that the intelligent species does not need to wait for population pressures to shift the ratios of traits, and can instead directly breed for the traits they desire.
A common misconception of the concept of evolution is that it declares that man evolved from apes or monkeys. This is not strictly the case as no modern species is the ancestor of modern man. Instead, the theory states that humans and modern primates share a common ancestor population, which branched into multiple species including modern apes, and modern humans.
The theory of evolution says nothing about the origin of life as a whole, merely how the incredible complexity and diversity of species came to exist after the creation of life. Abiogenesis, a different theory, posits that life arose out of nonliving chemicals.
This is a taxonomic issue, rather than a strictly evolutionary one. The current trend is to group organisms into monophyletic clades - that is, a group of populations or species that all evolved from a common ancestor. Since the most recent common ancestor of extant apes and humans was an ape, we inherit the moniker and are ourselves apes.
Just because our ancestors are extinct doesn’t mean they weren’t also apes.
Is there a backstory behind the original post? Or just as stated, “seeing what people hereabouts know about evolutionary theory”? if the latter… how’re we doing?
Following the OP, only reading the OP, first post:
I don’t really know where to begin, or how deep to get. Basically (how many people have said that yet?), the Theory of Evolution is about how the variety and diversity of life accummulated on this planet. It says that individual organisms have minute variations in form, and that through reproduction, those variations can accumulate in such a way that descendents can take on changes from their ancestors. Through the mechanism of many generations and lots of time, accummulated changes can shift from small to larger changes.
Evolution doesn’t really address how life first formed. However, embedded within the assumptions of evolution is that we can understand and describe the processes involved. Some people use this to draw conclusions about metaphysical and philosophical questions. Strictly speaking, Evolution doesn’t address those questions. The ability to understand those processes, though, does inform some assumptions made in those discussions and does affect the likelihood of some conclusions.
Evolution relies upon the mechanism of life itself - the genetic code that contains the instructions for how to build an organism. Reproduction of the organism relies on reproduction of the genetic code. How that code reproduces allows for changes in a couple ways. One is simple mutation - some environmental effect (chemical, radiation, etc) changes one of the chemical structures of the genetic code, which changes how that part of the code behaves, and that leads to a difference in the offspring from the parent. A second mechanism occurs in some types of organisms that rely on two parents instead of one to contribute genes. That kind of reproduction introduces changes by mixing contributions from two sources in different ways, which makes more variety possible.
The second factor that is critical to evolution is the environment - and by that I mean any and all conditions in which the organism must survive. Everything about that environment provides possible ways the organism could die, and therefore not reproduce, but by reproducing, it passes on its genetic material, and therefore the “species” continues. Each individual of that species finds itself with the same needs and the same controls it must overcome (i.e. predators, dangers, etc). But each individual is slightly different, due to those variations mentioned above. Ergo, some individuals are better suited to surviving particular dangers. Some find food better. Some avoid predators better. Some reproduce more, and thereby pass along more surviving offspring even if the individual itself dies.
Because of this, those sets of genes more suited to the particular environmental conditions are more likely to pass along, and those less suited are more likely to be eliminated. Variations accumulate, and the environmental controls provide a sense of direction to the changes. Things that help overcome dangers accummulate, things that make you more susceptible get eliminated. Neutral things can float along in the population because they are not actively eliminated.
Somehow the first living organism developed. Evolution doesn’t directly address this. But once this first organism developed and began reproducing, it began filling its environment to the fullest ability. The resources available made more organisms possible, which spread more and more. Eventually, organisms became dispersed enough to face different specific environments. And also, organisms changed their environments. Therefore, there did not remain one population of organisms that remained the same, but rather various different types that began to change in different ways to use different resources and have different strategies for surviving the challenges.
Over vast amounts of time, organism structures became more complex. Single-celled organisms became either symbiotic (e.g. mitochondria), or else collaborative and formed multicellular organisms. These became more complex, and differentiation of function occurred within these complex organisms, and the first plants and animals formed.
Continued adaptation, environmental changes, and deep time drove more and more changes, which created more and more diverse organisms, and spread them globally. Eventually, this process lead to the conditions of life on Earth today.
Is that what you’re looking for?
My idea in starting this thread was to elicit misconceptions about evolution so that they could be corrected, and in the process start a discussion or debate on the subject. I thought an interesting way to do this would be to get people to say what they think, in as much detail as they felt comffortable with, on the theory that unless Richard Dawkins is secretly a Doper, any person who did so would have at least one thing wrong. (I forgot to mention genetic drift, for instance.)
While perhaps not a misconception, it does seem that most folks’ understanding of evolution begins and ends with natural selection (with some basic genetics thrown in). A pity, really, since there’s a heck of a lot more to it than that.