Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Question About Evolution

  1. Sep 9, 2018 #1
    Hello all.. This is my first question here, i am looking forward to learning new things !

    As far as my understanding goes, evolution happens through small incremental changes to populations
    over time. Mainly due to genetic mutations..

    However, instead of small incremental changes, has there been any instances where a big change has occurred, which has had a very beneficial, advantageous consequence to the organism ?

    I have made up an example, just to help clarify my question..

    So, say for example.. Instead of a string of small mutations that led to our skull being bigger, maybe there was only one mutation, maybe in a transcription factor that led to our skull being 20% bigger..

    And the result of that was that our brains had space to grow and become more complex..

    Can and has something like this happened ?

    Cheers
     
  2. jcsd
  3. Sep 9, 2018 #2
    There are relatively few traits that are driven by a single gene or transaction factor. The most obvious one, that has occurred in multiple species over the years, produces short legs. Short legs are NOT advantageous to wild animals, but in domesticated ones, like sheep, it can be a big plus for the herders.
     
  4. Sep 9, 2018 #3

    stevendaryl

    User Avatar
    Staff Emeritus
    Science Advisor

    It's possible that a single gene change could make a big difference. However, there is a problem for big mutations in evolution, which is that if the mutation only arises in one animal, then that animal has to be able to mate with animals that do not have the mutation.

    I don't know whether one human having a much larger brain than his/her mate would be hard on their relationship, or not.
     
  5. Sep 10, 2018 #4
    The ability to digest milk beyond infancy must have quite an impact around 10,000 yrs ago.

    https://en.wikipedia.org/wiki/Lactase_persistence
     
  6. Sep 10, 2018 #5
    Oh yes, i had not thought about that. If only one animal had this mutation but did to reproduce then it would not get passed on.

    It could be very advantageous but the animal could get killed before reproducing for many, many reasons..
     
  7. Sep 10, 2018 #6
    Thanks for this. Somebody else mentioned this to me on Facebook. I will have a look into it !
     
  8. Sep 10, 2018 #7
    There are two camps on this. One adhering to the notion of punctuated equilibrium - evolution characterised by incremental changes at all times (Richard Dawkins most famous proponent) and others like Stephan Jay Gould (I believe it was) who propose that big evolutionary leaps in "one go" account for at least some of the major changes taking place. According to him there is no "law" or "principle" dictating that evolution has to be gradual.
     
    Last edited: Sep 10, 2018
  9. Sep 10, 2018 #8
    Dawkins argued that punctuated was still gradual, a period of stasis followed by small change, either a change in the environment stepping up natural selection or a mutation

    I wont misquote him so I will find out exactly what he said. I thinks its from the Blind Watchmaker. I am not sure if there is a paper so Ill look for that too.
     
  10. Sep 10, 2018 #9

    That's what I wrote. I may be confusing the terminology but he is of the gradual evolution school.
     
  11. Sep 10, 2018 #10
    Here is a quote from someone else i have been talking too..

    I thought i would post it as he raises some good questions that i do not know the answer too !

    "There are visible mutations present in bacteria and viruses all the way up to insects. We know it happens, but it takes many generations to accomplish. The biggest problem with humans is that we haven't had significant time to mutate and specialize as quickly as the geological record indicates.

    Modern humans very quickly appeared and dominated all other hominids. How do we explain the advent of the prefrontal cortex? What natural stressor created the need for such a mutation in only the highest order of mammals? What was the main driver of that mutation, and how did it happen so quickly?"
     
  12. Sep 11, 2018 #11
    I cant locate my watchmaker so I have wikied it. Dawkins was not keen on the punctuated idea, he said if the fossil record appeared to show no change then the population had simply moved elsewhere but were still evolving very slowly rather than in "jerks"
     
  13. Sep 11, 2018 #12

    Buzz Bloom

    User Avatar
    Gold Member

    I seem to remember reading somewhere a long time ago another interpretation of the punctuated evolution idea. The fossil record of a population might show no changes for a long time because the accumulated changes were hidden in a small fraction of the population while the environment remained very stable. Then when a sudden environmental change occurred the small population became the large fraction because it had properties better suited the changed environment. This would appear in the fossil record as a sudden punctuated change. I do not remember any examples of this in the fossil record, but there was a well known similar kind of example when some species of moth with white wings over just a few years of the industrial revolution changed to black winged moths due to the depositing of soot on the trees of whitish bark these moths frequently were on.
     
    Last edited: Sep 11, 2018
  14. Sep 11, 2018 #13

    lavinia

    User Avatar
    Science Advisor
    Gold Member
    2017 Award

    A few questions:

    - Similarly to the OP's question, I have wondered whether small genetic changes - where small does not necessarily mean a single point mutation - can lead to large phenotypic changes.

    - In the punctuated equilibrium model, is it possible that during a period of stasis/equilibrium where there is little selective pressure, a large number of mutations accumulate but have no or little selective advantage. But when a sudden change breaks the environmental equilibrium - e.g. an extinction event - selective pressure suddenly becomes important and the genetic background necessary for adaptation already exists in the accumulated pool of mutations that arose in the long period of stasis? Could this help explain rapid evolutionary bursts.

    - Since genetic information is the data for embryonic development, one imagines a computer like program - a sort of finite state machine - that translates the data into development. Mutations are important because they change the data and this explains abstractly how mutations are translated into modification with descent. So what about mutations in the genes that make up the computer program itself? How would those mutations affect modification with descent?
     
  15. Sep 11, 2018 #14

    Ygggdrasil

    User Avatar
    Science Advisor
    2017 Award

    Yes. For example, a mutation near antennapedia (antp), an important transcription factor in fruit flies, can cause the fruit flies to grow legs in the place of their antennae (hence the name of the transcription factor). https://en.wikipedia.org/wiki/Antennapedia

    Related to your third question, genes like antp that encode "master transcription factors" could be what you are thinking about. These master transcription factors coordinate the cells to produce many of the transcripts that give rise to certain cellular states and cellular identities. A major experiment in support of the idea of master transcription factors was the Yamanaka experiment, in which scientists demonstrated that injecting four transcription factors into an adult cell could reprogram the cell back to a stem cell state.


    Regarding the OP, here's a nice discussion about small effect and large effect mutations in evolution: http://blogs.discovermagazine.com/g...ation-mutations-of-large-effect/#.W5hCxs726Ul
     
  16. Sep 11, 2018 #15
    You also have a bunch of, as yet weakly quantified, epigenetic effects to consider.

    IMHO, a mutation which alters the degree of an epigenetic expression is far less likely to trigger speciation. Founder effect and genetic drift, certainly...
     
  17. Sep 11, 2018 #16

    BillTre

    User Avatar
    Science Advisor

    Here is an example of recent evolution that touches on punctuated equilibrium model and the source of mutations underlying geologically observable evolutionary changes:

    There is a world wide distribution of sticklebacks that live in saltwater.
    Opportunistically, saltwater sticklebacks will invade and colonize freshwater habitats and then adapt to those environments predominately by changing their use of salt and calcium (more limited in freshwater than saltwater) and losing some of their armour (spikes and hard surface plates, which contain a lot of calcium).
    These are simple morphological changes, rather than big changes in the way the animals make their living, but they are important to the fish and can result in a fossil record.

    This is a big issue for some people who like to research this stuff because along the west coast, from Canada up to Alaska there are many freshwater environments that appeared in the last ~10,000 years (a very short time in evolution) after the glaciers that used to cover those areas receded.
    This is like a playground for evolutionary studies and many have been made in the last 10 years or so.

    Detailed genetic studies of these populations have shown is that there are a set of alleles that have been repeatedly used to adapt to the freshwater environments (rivers and lakes, which are only connected through the ocean and are often rather similar to each other).
    These alleles are present at low frequencies in the ocean population and when the fish move into a novel different freshwater environment, they are positively selected.
    Here is a little Nature article on this.

    If seen from a geological perspective, this might seem as a very fast change in the animal's morphology (which is what you see in fossils), but the populations did not have to wait for mutations to form new alleles beneficial in the freshwater environment because the alleles were preexisting in the source population at low levels. (New mutations would also originate at low levels.)
     
  18. Sep 12, 2018 #17
    The Italian wall Lizard experiment gave rise to quick changes in decades, that would show up in a fossil record but somewhere else.

    Although this was a manufactured "selection," Island storms and drift wood could have produced a similar natural scenario.
    Would this be both a "jerk" and also an example of the wild type remaining pretty static whist an offshoot undergoes relatively large morphological change?

    I am sure both Gould and Dawkins would have claimed this one.

    https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2290806/
     
  19. Sep 12, 2018 #18
    Yes, there are 'controller genes' called HOX genes that determine when, during development, other genes are turned on and off. Mutations to HOX genes therefore can have large effects. Gould's punctuated equilibrium theory in part works because of these genes.

    There are other examples, too, where small changes to single genes have large, cascade effects, because of how those genes effect gene expression. For example, check this article out:

    https://phys.org/news/2018-09-gene-mutation-humans-optimal-long-distance.html
     
  20. Sep 13, 2018 #19

    Drakkith

    User Avatar
    Staff Emeritus
    Science Advisor

    The claim in this quote, that there hasn't been enough time for humans to evolve, is problematic. Our knowledge of the details of our own evolution, and of evolution in general, is not complete enough to support this claim. We know a great deal about the general mechanisms that enable evolution to occur, but we remain uncertain about how much time it takes for different traits to evolve and spread in complex organisms.

    Not only that, but when we talk about structures like the brain, we have to start taking into account social pressures on evolution. That is, evolution of the brain can be influenced by the structure of society and the ways that people interact with each other and society as a whole.

    I don't know what timescale the person has in mind. Human evolution stretches back about 5-10 million years ago (mya), the time our ancestors split off from chimpanzees. There is evidence of bipedalism from around 4 mya, perhaps as early as 7 mya, and brain size began to noticeably increase around 2.1 mya as seen in fossils of Homo Habilis. Homo Erectus fossils (1.9 mya) continue the trend by having even larger brains than Homo Habilis, and the general pattern is one of increasing brain size as we get closer to modern day.

    To try to shed some light on the questions from the quote I'm going to go at them one at a time:

    1. How do we explain the advent of the prefontal cortex?

    First, it's important to examine how we might go about answering this sort of question. The first thing we can do is to look at the function of the modern prefrontal cortex (PFC). A very basic rundown is that the PFC is involved in highly complex and abstract tasks such as complex planning (like your ability to plan out your day ahead of time), personality expression, decision making, and moderating social behavior. To quote a paper on the prefrontal cortex (link below): "The prefrontal cortex receives highly processed information from all major forebrain systems, and neurophysiological studies suggest that it synthesizes this into representations of learned task contingencies, concepts and task rules. In short, the prefrontal cortex seems to underlie our internal representations of the 'rules of the game'."

    Next we might examine a.) the physical differences in the PFC between species and b.) the differences in the above mentioned abilities between species.
    The PFC is much larger in humans than in other primates (and by extension other animals), even after adjusting for absolute brain size. This size difference also correlates with how much complexity an animal exhibits in the behaviors and abilities linked to the PFC, with larger PFC's correlating with more complex behavior. I'd give an example of the differences, but you really need to read the paper I've linked below. The authors of the paper do a far better job of explaining this than I can.

    Source: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1693009/

    Knowing that differences exist in both behavior and physical structure, we can make an educated guess that the prefrontal cortex evolved to facilitate more complex behaviors. That is, mutations that resulted in larger and more complex brains and PFC's endowed the organism with the ability to handle more complex tasks, better regulate its own behavior, understand the environment a little better, etc, all of which are beneficial. This then leads to an increased survivability of the organism and its offspring, helping to spread the mutation throughout the population. Obviously such a guess would need to be studied in-depth to determine whether it is viable or not.

    2. What natural stressor created the need for such a mutation in only the highest order of mammals?

    This question demonstrates a misconception that the person has regarding evolution. Evolution works by building off of what is already available. Large changes involving hundreds or thousands of new proteins and large-scale restructuring of DNA, culminating in substantially different body designs and functions, simply do not happen within the time span of even a few million years. You simply won't find them, as the chance that such a huge number of beneficial mutations occur without also incurring at least an equal number of detrimental, even lethal, mutations is vanishingly small. You might as well say that the first complex cell arose by sheer chance from a pool of simple molecules. (that didn't happen either)

    The reason I mention this is because the kind of changes in the PFC seen in the human lineage were only able to occur because the PFC was already as complex as it was. That is, the existing complexity of the PFC in the primate brain directly enabled the subsequent mutations to generate an even more complex PFC. And this isn't limited to the PFC. The entire brain structure of our primate ancestors had to simultaneously evolve along with the PFC, with the changes building off of what already existed at the time. Less complex organisms can't simply evolve a larger, more complex brain without also going through a very long process involving not only the brain, but the rest of the body, potential social structure, and many other factors. To put it bluntly, OUR LINEAGE is this exact process in action. One could say that the process of evolving a species with as complex a brain as ours from an amphibian species takes roughly as long, and involves roughly the same number and scale of changes, as it took for us to evolve from amphibians.

    Finally, we have to remember that evolution is still dependent on mutations that occur randomly within the genome. It's entirely possible that the chimpanzee brain is perfectly capable of evolving into one just as complex as ours, but that the right mutations, in the right order, and subject to the right pressures, simply haven't occurred for them.

    3. What was the main driver of that mutation, and how did it happen so quickly?

    The answer to that question is simply not known at this time. It's very difficult to distinguish between cause and effect when looking back hundreds of thousands or millions of years at species that we only know of through a small number of fossilized remains. And we haven't been studying evolution for long enough to observe such large changes in a species. But that doesn't mean we can't try to answer the question, and scientists are doing exactly that as we speak. A number of references on this exact topic are given in the encephalization section of the wikipedia page on human evolution: https://en.wikipedia.org/wiki/Human_evolution#Encephalization

    The questions posed in the quote are indeed good questions and scientists are currently working to answer them. However, the fact that questions still exist is not necessarily a 'problem'. That is, it does not detract from evolution in a general sense and, as yet, does not detract from the details of human evolution as posed in various models. Science's entire purpose is to answer all the questions that arise when you start to look into how the universe works. There will always be unanswered questions as long as we have the capability of doing meaningful science.

    I just noticed this as I was finishing up the rest of the post above. I don't know why the person stopped at insects when referring to mutations. Every single species that we can observe, including ourselves, show numerous mutations. Just about every cell in your body has a slightly different DNA makeup thanks to mutations that occur during the cell's lifetime and upon cellular reproduction. Even cancer is a product of evolution in the sense that a population of cancerous cells evolved from a population of non-cancerous cells through the mutation of several key genes. There's even an infectious (i.e. can be transmitted) type of cancer that affects dogs that evolved from plain old non-cancerous canine cells. One could potentially classify this as a different species, consisting of a unicellular, asexually reproducing pathogen.
     
    Last edited: Sep 13, 2018
  21. Sep 19, 2018 #20
    I was thinking that most of this threat is focussed on the gene mutations which may very well be fairly predictable and occur at a steady rate but that doesn't describe evolution. There is a huge amount of variation in a population and many of these variations will be pretty irrelevant but if there is a sudden environmental change in which a low frequency genetic variant allows survival and those without this variant die we could very easily see a very rapid change. There appear to have been several episodes in human history were environmental events have caused populations to plummet and which have caused huge changes in the genetics of the species.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted