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18

One of the main points of contention in the study of virus evolution is whether or not they appear before the last universal cellular ancestor (LUCA) or afterwards (commonly accepted: genes that "escaped" from host organisms aka the escape hypothesis or vagrancy hypothesis). Basically though, the LUCA is the most recent ancestor that all organisms living on ...


11

The answer is chance or, even better, contingency. About your calculations, it is true that the theoretical sequences are almost unlimited, but the basic scaffolds are not. Very different sequences can fold into the same basic scaffold and have a similar reactivity/function. So, even if not all the sequences have been explored on this planet, most of the ...


9

There were many (more or less) non-theological theories of how life had developed before Darwin, starting at the ancient greeks. Many theories included spontaneous generation but also aspects of modification by descent of existing species (i.e. evolutionary change), but most were not that well developed and complete thought. However, one of the more complete ...


7

Great question. There are several hypotheses, but in reality no one really "knows" because this is incredibly difficult to prove. We may never know for certain. Anyway, on to the three main hypotheses, I got this from http://en.wikipedia.org/wiki/Viral_evolution, I think you'll find it to be helpful. "There are three classical hypotheses on the origins of ...


7

Cats and monkeys have a common ancestor, both are placental mammals, so at the very least they must have both evolved from the first placental mammal. Cats are members of the Laurasiatheria group and primates are members of Euarchontoglires. These groups of mammals probably split off from each other about 100 millionish years ago. For more information about ...


7

I would consider HeLa cells to be an example of a unicellular eukaryotic organism that evolved from humans. It can survive independently and replicate within cell culture plates, but cannot survive in the wild, however. HeLa cells are, like in your example, cancer cells, in this specific case human cervical cancer cells. They were propagated as an ...


6

"Evolving from another species" versus "Most Recent Common Ancestor (MRCA)" One cannot say from two extant species that one evolved from the other. It just doesn't make any sense. It is not only true for cats and chimpanzee but it is true for any pair of extant species. One extant species has never evolved from another extant species. However, one can say ...


5

I think that the most important point has been given by CactusWoman, when (s)he says "Just because you cannot forsee a use for more "bulgy" spikes doesn't mean there isn't a use for them." In addition to that, I would like to say that several plants evolved traits that were beneficial at a time where other herbivores existed and that are now useless. Those ...


4

Just because you cannot forsee a use for more "bulgy" spikes doesn't mean there isn't a use for them. Furthermore, natural selection isn't about producing perfect organisms, it's about selecting for traits that are "good enough". There is also more to evolution than natural selection. The phenomenon of genetic drift can cause a neutral or slightly ...


3

Could not fit in a comment... To my understanding, paralogs and orthologs refers, as you said, to the relative isolation of gene copy to the isolation of populations (and eventually species). Gene conservation on the other hand refers to the variability of a given gene along many species. If a gene does not show any variance along many species, than we ...


3

Inspired by the answer by @MarchHo, I came to think of the contagious cancer that attacks Tasmanian Devils - Devil facial tumour disease - which should provide a very similar example to the clams in your question. I don't think it has been given a species name though, but for most purposes it functions as an independent species. This "organism" lives as a ...


3

The writings by Samir Okasha (philosopher of biology/science) could be a good starting point. In his book Evolution and the Levels of Selection, he explicitly uses the Price equation to discuss selection at multiple levels (e.g. chapter 2.3: Price's equation in a hierarchical setting), and also derives a multi-level version of the Price equation: ...


3

The most obvious answer to your question is that the enzyme responsible for nitrogen fixation is inactivated by oxygen. So photosynthesis, which produces oxygen, rules out nitrogen fixation, and, as you know, plants photosynthesise. However, they could have evolved specialized cells for nitrogen fixation, which do not photosynthesise. In fact, some colonial ...


2

First of all, there is a very heated debate about this in the field of social evolution at present, and you aren't likely to get a conclusive answer. One theorist may give you one answer, but another will vehemently disagree. I'll start by logically answering your questions in reverse order! Question 2: Can you please provide an intuitive explanation of why ...


2

I think the opposite list---what features of life might be reasonably expected to be the same elsewhere---would be much shorter. Nearly every feature of life on earth as I can think of it is arbitrary in the particular molecules. DNA. Why only 4 bases? Why the bases that we have (ACTG)? Researchers are able to create organisms with expanded DNA alphabets ...


2

Is background radiation a critical component of evolution? No, it most certainly is not. The DNA replication and DNA repair mechanisms aren't perfect and errors happen without any external cause or catalyst. You could say mutations happen on their own. There are mutagens that also cause DNA damage or mutations, but they're merely affecting the DNA ...


2

According to the known phylogeny of Anserinae in this paper, Cygnus atratus (the black swan) is most closely related to Cygnus melanocoryphus (the black-necked swan). All of the other swans in the genus Cygnus are white, or close to white. Therefore, it is reasonable to assume via maximum parsimony and maximum likelihood that the two genera evolved ...


2

His notion of systemic mutations involved the postulation of massive chromosomal rearrangements (not mere recombination/crossing-over) as mediators of speciation in one-step. While whole genome duplications have been shown to induce speciation (see, for example, cryptic speciation in Hyla versicolor) they are not large scale rearrangements as he suggested. ...


2

Crows and gulls would probably also flee predators but their songs are definitely not really pleasant to listen to! I know it, they woke me up last week-end $\ddot \smile$. The canadian goose or the common starling (see here) are other examples of not really pleasant songs. Too a selectionist view of evolutionary processes It is important not to make the ...


2

From the pheno-geno map and the genotypes frequencies, you have the whole distribution of phenotypes in your population. The mean of the phenoype $n$, $P_n$ is the $$\bar P_n = \sum f_{G_i} P_{G_i}$$ , where $f_{G_i}$ is the proportions of individuals having genotype $G_i$ and $P_{G_i}$ is the phenotype of the individuals with genotype $G_i$. Therefore, ...


2

I'm not sure I understand the question. You've elegantly demonstrated that only a tiny fraction of all protein sequences could possibly exist, but then asked why only a tiny fraction of all protein sequences do exist. Your conclusions about independent origins of life having no proteins in common are accurate, but also consider that you as a human being have ...


1

Yes, of course they are conserved. Conservation is basically a measure of sequence identity. It can be used to describe the relationship between both paralogs (genes created by a duplication event) and orthologs (genes created by a speciaton event). Any type of homology relationship can be described in terms of the conservation (sequence similarity) between ...


1

Yes, it has very much to do with the poliploidy events. Specifically if you look at the grasses, most grasses that are diploid (eg., AA, BB), cannot hybridize, but in some rare events when they form polyploid (AAAA, BBBB), they can readily hybridize to form fertile progenies (AABB).


1

Behaviour I would think that the most important causal factor between this difference is behaviour. Men probably smoke more than women, probably eat more junk food and are eventually more stressed. Men also probably take more risks and have more accidents. This last point might have been very important at an earlier time when men were hunting outside while ...


1

Gradualism is the view that large-scale changes occurs by the accumulated effects of small changes over long periods of time, rather than by rare cataclysmic events of massive effect. Uniformitarianism is the view that the same forces that shaped the world in the past continue to operate today. Historically, uniformitarianism has often included aspects of ...


1

It is not essentially asexual reproduction that causes mutations. Mutations can be caused because of errors in DNA replication which can happen during both mitosis and meiosis. Mutations can also be caused because of error-prone DNA repair mechanism. Other than these intrinsic factors there are physical and chemical mutagens that alter the DNA or ...


1

1.Is such an approach trying to quantify homology? Which i know is not correct as homology is qualitive measure. A common approach to identify orthologs (homology between two genes resulting from a speciation event) it 'best bidirectional match': if you blast gene A (in species 1) against all genes of species 2 the best match is gene B, and if you blast ...


1

Deinococcus radiodurans did not "develop resistance to mutations". It is able to repair its chromosome when scatered in pieces by radiations or desiccation, while other bacteria would die in such conditions. So this is adaptive in extreme environments, such as deserts (where it has evolved) or canned corned beef (where it was discovered).


1

It is not a regression (not at this stage of the paper, a regression will be done latter) The only complicated thing to understand is $b_i$, which is the 'base relatedness', ie how $i$ is related to a random individual (to be compared to how related it is to individuals with whom it interacts). To simplify let's first consider the situation where $b_i = ...


1

There are several subconcepts within the concept of robustness. Several definitions exist for all of these concepts and I am just suggesting one variant of the possible definitions below. Mutational robustness Might be defined as a function of the mean and variance of the distribution of mutational effects. Environmental robustness Might be defined as ...



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