Natural Selection - confusing questions

    Darwin’s evolution through natural selection states that organisms in a population have a degree of genetic diversity and thus some are born with slightly different traits. The traits that are more conducive to their environment and thus help them to better survive, gain resources, and reproduce may be passed on to their progeny, while traits that are not conducive to their survival and reproduction are not generally passed on as much. This means that the favorable traits are selected for by nature. If they are better adapted to their environment, then they have a better ability to reproduce and reproduce more, thus increasing their genetic fitness and the frequency of this trait. Their offspring will have these traits and will also be better suited to adapt to their environments. 

How can the presence of natural selection NOT necessarily lead to an evolutionary change? There can be a selecting presence that favors certain traits, but if those traits are not inheritable, then evolution would not occur. I cannot think of a single example in which a trait would be affected / selected for but not then inherited by the offspring. Several genotypes can influence a single phenotype (epistasis) and conversely several phenotypes can be affected by one gene (pleiotropy). I’m trying to think of a scenario in which the phenotype may be affected, but the genotype is still present. Maybe the genotype is still carried and thus the allele frequency in the population stays the same, but the genotype is just not expressed? If the genotype is not expressed, even though the organism contains the genotype, then the phenotype will not be expressed.  

I am also confused by the question “Can you explain how selection might happen in the absence of natural selection?” We have previously defined natural selection as “The process in which individuals with a particular trait tend to leave more offspring in the next generation than do individuals with a different trait.” Based on this definition, basically all other types of selection - sexual, behavioral, kin, etc - are forms of natural selection. Mutations, random mating, migration, and genetic drifts can cause evolution that is not related to natural selection, but they are not forms of selection. There is no force that is selecting for or against something. These are all more or less random changes that can occur. There is artificial selection where humans get involved and purposefully select for traits. I think most people think of traits humans have selected for in dogs in order to create specific dog breeds. See my post about Elephants and Evidence of Evolution for arguably another example of artificial selection.

Comments

  1. Ashlynn KennedyFebruary 18, 2021 at 12:09 PM

    Hi Erin! I like your title and agree that there are some confusing questions when it comes to natural selection and it's hard to think of ways to best describe them. I can also only think of artificial selection being the only selection that is not natural selection. In my post I talked about humans breeding pigs to be the best market hogs.

    ReplyDelete

Post a Comment

Popular posts from this blog

Cloning - Part 1

Image
          Baby Elizabeth Ann, the cloned black footed ferret           Recently, I have read a couple stories of animal cloning in the name of genetic diversity. I think these are interesting topics and relevant to the class. In August of 2020, a critically endangered animal called Przewalski’s horse was cloned from the DNA that had been collected in 1980 and preserved in the San Diego Zoo Global. With conservation efforts, the species was brought back from the brink of extinction and re-introduced to its native grasslands in China and Mongolia. What I think a key point to consider is that almost all of the the horses can be traced back to only 12 predecessors. Conservationists were only able to work with the genetic diversity of 12 horses - that is how critically endangered they were. The new baby that has been cloned using old DNA is meant to contribute genetic diversity into the dwindling species.  In December of 2020...
Read more

What is Evolution? Fact or Theory?

Evolution is the process in which organisms change or adapt to better fit their environment and/or cohabitate/survive with the other organisms in their environment. I add the second part because organisms can evolve together. Last semester I took Organismic Biology, and I learned that moths and bats constantly evolve to outwit one another -- moths to stop bats from eating them, and bats to keep being able to eat the moths. Bats have developed echolocation to be able to find moths in the darkness of night. The echolocation sends sound pulses which bounce off objects/organisms and allow the bat to determine what the sound waves hit and its position. Moths came up with the ability to emit their own sonar to either block the bat’s waves or confuse it, and some moths developed the ability to send sounds that signaled that they were poisonous or would taste bad. This is an example of behavioral evolution, and the moths and bats have coevolved. Here is a link to a youtube video with more i...
Read more

Elephants and Evidence of Evolution

Image
       One of Darwin’s key predictions of evolution was that species change through time. This is dubbed as microevolution. When considering current evidence of evolution, I like to think about how humans have affected the evolution of other species. Most effects are done inadvertently. As I said in one of my previous posts, I love elephants. I remember reading a couple years ago that the amount of poaching of elephants in Africa for their ivory tusks has led to more elephants not developing trunks. Humans have poached and killed the elephants that have tusks to take their ivory, but they do not kill the elephants that do not have tusks. The poachers have thus selected for the tusk-less elephants. National Geographic reported that between 1977 and 1992, 90% of elephants living in a national park in Mozambique were killed for their ivory. Before 1992, 96-98% of female elephants developed tusks, but after 1992, only about 32% of female elephants developed tusks. Even m...
Read more