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17

During the process of selection, individuals having disadvantageous traits are weeded out. If the selection pressure isn't strong enough then mildly disadvantageous traits will continue to persist in the population. So the reasons for why a trait is not evolved even though it may be advantageous to the organism, are: There is no strong pressure against ...


13

There's always the most obvious: Evolution is chance. Some traits allow an individual to have a higher chance to produce offspring. That doesn't mean individuals with that trait have more offspring, not even on average, unless the law of large numbers applies. A randomly mutated perfect squirrel could appear, and since it's only one, it gets run over by a ...


5

It has been a long time since, I've read The Origin of Species, but it sounds like the intent of the phrase is to suggest that the presence of similar characteristics in two species do not imply that they are related, but that related species would be expected to share characteristics. I.e. that similar characteristics do not imply relatedness, but ...


5

There exists a bunch of population genetics forward and backward (coalescence) simulation platforms. Here is a non-exhaustive list. They all differ and you'll have to go through their manual to see what is more adapted to your needs. Here is an exhaustive (or almost exhaustive) list of such platforms. Some are more known than others. Personally, I already ...


5

Male mice lack nipples too. Mice are frequently used for embryonic research as they are small and reproduce quickly. It is thought that male mice do develop nipples, but that they regress during development (Wysolmerski, 1998). In general, it is thought that mammalian organisms develop as females by default when there is no male (Y) chromosome present ...


5

Resemblance between parent and offspring is certainly true. Some traits are more obvious than others, for example skin colour would be very obvious. As babies mature they will gradually begin to look more and more like their parents, the features of babies often change rapidly, for example pretty much every baby has a little nose, but by the time they are a ...


5

The answer in extreme brief is yes. Only about 9% of whites and 16% of blacks engage in interracial marriage in the U.S. But really this deserves a fuller discussion. The predominant pattern of mate selection in human beings is to marry within their ethnic group. I say 'ethnic group' rather than 'race' because 'race' has no strong scientific ...


4

Genes that were once functional but no longer are are called pseudogenes (as Corvus pointed out in the comments). Many genes that are similar today (homologs) are hypothesized to have come from duplication events in the past. In most cases, these duplicates diverge. The divergence can happen in several ways: 1) one retains the original function while the ...


4

Below are reasons I can think of. The list is not an exhaustive and there are some conceptual overlaps. I have to say it is kind messy but one can hardly make a list without overlap for this question. The trait seems advantageous but it is not, maybe due to its effect on another component of fitness (trade-off). It sounds to me to be the most likely ...


4

Because evolution is an effect, not a cause. That is, there's no "God of Evolution" http://wiki.lspace.org/mediawiki/God_of_Evolution out there deciding that this or that trait would be beneficial to a species, and deciding to add it. Evolution just works* on whatever random variations happen to come along. *And as others have pointed out, it works ...


3

Looks like some parasitoid wasps have zinc coated barbs on their ovipositors which may function to help them bore through wood and lay their eggs. Here's the blog entry about it on IFL Science, and the original article: parasitoid ovipositor specimens had a weight percentage of zinc of 7.19±3.8% (N=42) in the tip regions, which was significantly higher ...


3

The $sR$ that your looking at is the average relatedness of the next generation. This assumes that the new immigrants into the the population are completely unrelated. So if the population is completely viscous ($s=1$) the average relatedness of the next generation equals that of the current generation. On the other hand, if the population is not viscous ...


3

Animals with a "front" and a "back" are known as Bilaterians. There is ongoing scientific debate about what the most recent common ancestor of the bilaterians, or "urbilaterian", was like. One proposed form is a simple wormlike animal with some form of eyelike structures, a segmented body with internal organs, and a centralized nervous system. This is ...


3

We generally define a "head" as something that comes at the top/front of the body. I think that, we're likely to ignore examples of animals with nervous systems / sensory systems not at the top/front of their body as "animals without heads" rather than "animals whose heads are not at the top/front". For example, sponges and jellyfish. Some animals who do, ...


3

I will focus my answer on the evolution of orb web spiders (Fig. 1), because arachnids, like insects, are relatively non-complex creatures with an obvious systematic behavior (the weaving of highly symmetric, repeating structures). Hence I reasoned this would be a good approach of investigating the answer to this question. The orb-weavers (Orbiculariae, an ...


3

This was getting too long for a comment but this should at least answer your question to some extent. Gliders do not actively fly and there is no work done by them in producing motion. Other flying machines do make sound. If a trait exists then it means that there is not enough pressure against it. You you can hear a mosquito only if it flies close to ...


3

If you're willing to accept many orders of magnitude and define life as the Last Universal Common Ancestor. For the rest of this answer, life begins 3.5 Gya with cyanobacterial mats and stromatolites and so on. Genetically the LUCA is dated to around this time, which matches the fossil record and everything's great. The LUCA can't have sprung from ...


2

It seems like you are attempting to frame this as a question about current evolutionary theory. However, current evolutionary theory doesn't expect anything as complex as an organ to arise spontaneously without any precursors. You suggest a new claw in an insect would be something "spontaneous" enough for you. This again shows that your question and the ...


2

As you probably know, there exists many different species concepts (or definitions of species). Often, you see a separation into at least six different categories of species concepts, which are then often subcategorized futher (and they can also overlap to some extent), namely: Biological species concept Phylogenetic/cladistic species concept Evolutionary ...


2

There are few subjects that yield to as many semantic issues than the definition of species and the definition of life. Your question is at the border of the species definition. Therefore the question is not so much about Biology than about Philosophy, so let me advertise: The following answer is nothing else than a semantic discussion (philosophy) and has ...


2

Here there are a couple that I own: The "classic" from Uri Alon touches many of the topics you mention. It is easy to read and goes relatively deep into the methods. There seems to be a new edition (if you search it in Amazon it will pop up), but it was planned for last year's April and then delayed so no so clear when will be actually published. For the ...


2

I've seen this termed "phylogenetic pseudoreplication", but I can't remember offhand where. I'll see if I can find it. Without a tree, the boxes and Xs essentially represent 2 data points. As Remi.b suggests, this is really just high phylogenetic signal.


2

Your question is really good, but in actuality, they do evolve towards muting themselves, actually, they have pretty much done "most of the work": It is assumed that microscopic scales along veins and wind margin play an important role as a silencer as downs on the flight feather of owl. From this we can assume that the effectiveness of these scales are ...


2

The process of evolution is a change in a population over time through changes in the heritable variation, and visible as changes in traits affected by the heritable variation (such as that in the DNA). This implies that, if a trait evolves over time, some kind of change has occurred in the genetic composition of a population. Here follows a ...


1

The question carries the assumption that the trait the asker refers to, has never been expressed in that organism. The trait may have evolved, and been unsuitable for the ecosystem in which the organism existed, and selected out. The trait may not have been able to evolve from the DNA code available, in the ecosystem in which the organism existed. That is, ...


1

I'm not sure when the concept first arose but I would assume it was after Darwin had come up with the Theory of Evolution. The concept I am talking about is "Convergent Evolution" which in essence explains "characteristics do not make the genus". Convergent Evolution is the concept that two completely different organisms, given the same selection ...


1

Mutations in DNA or RNA sequences do not necessarily result in significant changes in the functions of the proteins they encode (or in the case of RNA ribozymes, ribozyme function ). This is because, for a variety of reasons, the change in DNA/RNA sequence may not significantly alter the structure and function of the ribozyme/protein (the function that ...


1

When you calculate the PICs of a trait, you are making a statement about how that trait evolved. The purpose of PICs is to account for phylogenetic non-independence. However, when you are comparing two analogous traits, those two traits are in fact phylogenetically independent of each other; they do not share a common origin. Thus, I think it would be an ...


1

I think you need to consider the overall amount of information that is needed to implement a proper control system in living organisms. In prokaryotic cells, in most of the cases, you will find that one gene code for one enzyme, so if a simple organisms need 500 enzymes to stay alive you can expect 500 genes that code for that enzymes. A more complex ...


1

Here too is a speculative answer, but evolutionary why questions are many times speculation, as it cannot be directly scientifically tested (there are no animals with a head in their tummies), only inferred in retrospect. I will sum up a few reasons to build the eyes and ears into a solid, rotational structure and not in the torso: The eyes are hardwired ...



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