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10

As a couple of counterexamples, species in the classes Symphyla (Pseudocentipedes) and Pauropoda within Myriapoda have 8-11 and 12 leg pairs respectively, so between 16 to 24 legs (sometimes with one or two leg pair stronlgy reduced in size). (species in Symphyla, from wikipedia) Another common and species-rich group with 14 walking legs (7 leg pairs) is ...


5

The straight forward answer is: we don't know. We don't have any direct evidence for what happened at that time nor any completely developed and coherent theories for how it worked. The widely believed hypothesis is the "RNA World" hypothesis. RNA, unlike DNA, is capable of spontaneously folding to form catalytic molecules and thus avoids the needs for ...


4

Why organisms reproduce If they didn't reproduce, they would die out. More concretely, suppose an animal is born with a mutation that removes the desire to reproduce. That animal will not have any offspring, so its genes will not be passed on to the next generation. When that animal dies, that mutation will die with it. Why some organisms reproduce a ...


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Poison dart frogs have aposematic colouration, making them the exact opposite of camoflaged. They are also predators, since they feed on ants, termites and beetles.


4

There are a few issues your question brings up. First, the idea that species evolve from simple to complex is actually not a prediction or inevitable consequence of evolution by natural selection. The terms "simple" and "complex" themselves are ill-defined. For instance, if you defined "complex" to be size of the genome, the most complex organism found to ...


4

There's really two answers to the question. The first is overall symmetry: mammals, like all tetrapods, are bilaterally symmetric. This comes from a distant common origin with other bilaterally symmetric organisms. Organisms which evolved from this common ancestor often have organs in pairs, probably evolving as a re-use of regulatory genes. The other ...


3

Crossing over primarily happens because of homologous recombination (HR). From the molecular point of view, it can happen between any homologous regions and it is not necessary that an entire allele has to be crossed over. During the process of HR, a DNA double strand break occurs. This is followed by resection (exonucleolytic degradation of one of the ...


3

People who think in creationism or think about species rigidly might have a bit problem with that, so let me describe an example: When are humans "adult"? Legally, at 18 (or your national equivalent). However, everyone understand that people are becoming adult gradually. Sometimes, they "age" very quickly after some harsh experience (16 years old student ...


3

What is a predator? As discussed in the comments by @MarchHo and @AMR, there is discrepancy between the definition of predation in the biology literature and in the every day use. Population definition From the Oxford dictionary predation- The preying of one animal on others; the behaviour of a predator (predator n. 2); (also occas.) an instance of ...


2

Here is how I would explain what a genetic signature is: A genetic signature of a certain type of evolutionary history (type of selection or demography) refers to the effect that this specific type evolutionary history has on genomic properties of populations.* We are interested in understanding such signatures because knowing the asociation between a ...


2

It is, of course, not just mammals, but nearly all animal life is symmetric. Even plants are usually symmetric in some degree. There are exceptions here and there. For example, one interesting exception is that of the fiddler crab which has one claw larger than another. In general, when a single appendage is present on an animal it is nearly always on the ...


2

Here are a few metrics you can calculate to get you started. You can use R to perform these calculations. Net Diversification Rate (r) Net diversification rate is (rate of speciation - rate of extinction). You can calculate it using the bd.ms or bd.km functions in the geiger package for R. r = 1: r = 2: Tree Imbalance: Colless index (I) Colless's ...


2

I could be misreading your question, but it doesn't sound very specific. Rather, it sounds like you're asking "How can I make sense of all the various color schemes employed by venomous species?" So I'll take a stab at it... Animal coloration is a very complex phenomenon, with a number of overlapping physiological traits, evolutionary strategies, etc. ...


2

Welcome to Biology.SE Issues with the question It is impossible to correctly answer this question as the phrasing is so fantastically unclear, wrong and misleading (no offense, really). I will give a few points here that may help you but the only thing you can really do to answer your own question is take some time to follow an introductory course to ...


2

I can think of two factors that would influence this, but there are probably more. 1) How do transposable elements (TE) get into the genome in the first place? The answer is both vertically and horizontally. Vertical transmission needs no explanation. Horizontal transmission of TE has been documented in several cases. In some cases, infectious agents ...


1

I am not sure exactly what you are after when asking "how did these glands came?". It seems that you wrongly believe that similar glands do not exist in other primates. Here is a short answer that will help you to search for more information about the evolution of these glands. Chimpanzees and Gorilla also have sweat glands. The use of sweat gland in ...


1

Yes, primitive earth was more exposed to radiation as a result of the Earth not having gaseous oxygen during the Hadean eon (which was formed after the oxygen catastrophe as a by-product of cyanobacteria's photosynthesis), which could form ozone and the ozone layer. As a result of the absence of the ozone layer, ultraviolet radiation would not have been ...


1

One of the comment to David's answer (which covers the history and reasons for spiderwebs in its two links) mentions a comparison between web patterns and molecular phylogeny. Not precisely that, but I found this article which opens up some interesting possibilities (I can delete this or turn it into a comment if you consider it too unrelated, please let me ...


1

The key point is that the first equation is describing frequencies, i.e., $\sum_{i=1}^n x_i = 1$, so there are only $n-1$ degrees of freedom. For instance, if $n=2$ (as in Hawk-Dove), you can totally describe the state of the system with just $x_1$, because $x_2$ is just $x_2=1-x_1$. This constraint is enforced by adjusting $\phi$. To convert the ...


1

If single cells are capable of surviving on their own then why did multicellularity evolve? This situation can be compared with the evolution of family and society, in a way; during the time of crisis, the survival chances increase when someone stays in a group. Similar conditions would have resulted in the evolution of multicellularity. The difference ...


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There is an interesting theory coming from a slightly different, yet related, field. It was developed by Paul Vasey and Doug VanderLaan of the University of Lethbridge, they are both evolutionary psychologists: An Adaptive Cognitive Dissociation Between Willingness to Help Kin and Nonkin in Samoan Fa’afafine (or direct link) They called their theory the ...



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