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As I have already mentioned in my other post, the most important role of urea synthesis is blood pH regulation, so it is not just about excreting a waste product... The urea is created from NH4+ and HCO3- in the liver (mostly) and the kidney because of blood pH regulation purposes. It neutralizes the HCO3- created by the lungs from CO2 and OH-. The urea ...


0

Our knowledge about the sexual transmission of mitochondria and plastids (hereafter organelles) in isogamous eukaryotes comes mostly from studies of the yeast Saccharomyces cerevisiae and the green alga Chlamydomonas reinhardtii which are both unicellular species. To investigate organelle inheritance in a multicellular organism with ...


2

This just got too big for a comment and I think might actually qualify as an answer. Can you give me a source for what you're reading? According to this, which matches the definitions you are using, K=(Nu)/N=u where K is the substitution rate, u is the mutation rate in the population, Nu is the individual mutation rate, and N is the population size. I went ...


0

Suppose a gene performs two distinct functions 1 and 2, both of which are essential. We'll call this gene A, for ancestral gene. A duplication copies A to another locus. Now there are two genes, A and B, that perform the same two functions. At this point, if either A or B is deleted, the organism is fine. Over evolutionary time, A and B undergo genetic ...


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LUCA was the LAST universal ancestor not the first. Naturally it competed with other extinct species. My reseach suggests that LUCA was resulted from the fusion of 2 genomes. The evidence for this is that on reconstructing the amino acid sequences for LUCA enzymes we find some contain no cystine but do contain tryptophan or the opposite.


1

There are many different ways to do this, depending on what assumptions you make on e.g. stable age structure, distribution of offspring, haploidy/diploidy, population growth etc. As you probably know, there are also two main approaches to effective population sizes, namely ones based on; 1) the rate of inbreeding ($N_{e,i}$) and 2) the increase in variance ...


1

From Conner and Hartl's A primer of ecological genetics: "Any variance in reproductive success among individuals greater than random expectations, a commonplace concurrence in natural populations, reduces effective population size." So yes, selection does reduce the effective population size and for the reason you suggest - it removes some ...


2

You can't predict the evolution of anything because evolution is driven solely by the environment. It is the environment that squeezes species into to specific forms. We have has a much say in our shape and form as a whirlpool does and for the same reasons, both humans and whirlpools result form powerful outside forces. In order to have shot at even making ...


0

There are multicellular organism which do not actively eat other organisms, however, there are no organisms period who do not kill other organisms. Trees, and other vertical plants, evolved in the first place in competition for sunlight. For plants, being in the shade is like smother or starving a human since they literally use sunlight to create and ...


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Yes, plants! Plants are autotrophs. While Animals and fungi are heterotrophs. Have a look to the wikipedia articles. In short, autotrophs organisms are organisms that synthesize their own compounds from inorganic compounds. Heterotrophs organisms are organisms that synthesize their own compounds from organic compounds. Therefore, any multicellular plants ...


2

I don't fully understand how your model works I don't fully understand how you model your population. Is it a standard $oop$ (object-oriented programming) where you simulate each individual? Or is it a simulation where you already use some mathematical model? You could eventually copy-paste your code. it is probably not very long, right? What language did ...


1

If rates of meiotic recombination DIDN'T vary across species - THIS would require an explanation! After all, evolution creates diversity, not homogeneity. I can only wonder that more recombination would allow for a faster diversification. The more DNA you shuffle, the more distinct each individual offspring may be (though I'm not 100% sure). The ...


1

Could not fit in a comment... This post (and the excellent answer from Richard Smith-Unna) lists the species that have the smallest genome that we are aware of in different clades. Yes we can/could sequence these tiny genomes and try to understand what each sequence does. I think that to understand the minimum requirements for life you will mostly be ...


4

You can have a look to the most basal branches and you may get a pretty good idea of what those early plants looked like. What we call plants is what we call plantae or Archaeplastida in Latin. This clade contains the red algae and the green algae. Within the green algae are the land plants. In the land plants are the embryophyta which contain all what you ...


2

I don't think it is a clever thing to group all types of decussation and look for a general explanations. I would tend to think that different decussation have different explanations. It is like asking what are the hypothesis to explain evolution of body size. There is no general answer to that but only a list of case specific impact of different factors on ...


1

You can see the wikipedia article on meristem. The apical meristem differentiates into floral meristem that gives rise to flowers. From this the cells specifically expressing APETALA3 (AP3), PISTILLATA (PI), AGAMOUS (AG) and SEPALLATA (SEP) would give rise to the stamen [ref]. CRC gene is essential for female development and plants lacking this will not ...


1

The problem with Intelligent Design is that it doesn't appreciate that the forces that shape species (and individual organism) have to be constant and ongoing or the species disappears. The past matters little, it's what happens right here, right now that keeps species in any particular form. Biological system are not static structures like a building. You ...


1

"I imagine that turtle looking up at that food, and sub-consciously wishing to get to it, constantly straining, for it's entire life time. It seems plausible to me that we (advanced life) could have a biological mechanism to "write" needed alterations into either our own DNA or our reproductive DNA over time, triggering the very specific ...


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Evolution is about descent with modification. Spontaneous generation doesn't have that. It's about modern organisms emerging from raw molecules. If flies spontaneously appeared from rotting cow meat, why would they have DNA that made them look like they were evolutionarily related to other insects?


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You are right in the sense the evolutionary biology doesn't try to explain the origin of life as it is not within its scope. Other fields of biology investigate the question of origin of life (abiogenesis). Now, there is a very important difference between spontaneous generation and evolution. Life originated at some point and the through repetitive ...


2

Here is a more morphologic, less genetic answer: According to this article, the 2 sets of paired appandages (shoulder and pelvic) was set in stone when agnathans transitioned into gnathostomes (ie. when the first vertebrate organisms began to evolve jaws, an anatomic change that allows for classification of different stages of history found in the fossil ...


1

This article claims to be a new level of evidence for group selection. Its a little early to tell at this point whether the critics will be moved. They have not been in the past! sorry if this is a bit short - its late, but i'll try to come back and do more later..


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The answer by Remi.B is excellent, I'll just attempt an explanation by way of gene networks: In genetics we see new genes "linking" to the older genome by regulation pathways and by being "fit" only in the context of the existing genome. This has the effect of making the older genes indispensable. Change them and you rupture the whole mesh. If you want to ...


7

I think I might interpret your question as asking, not just why don't mammals have more than four limbs, but why arthropods have more variety. Insects have six, but others have eight, ten, or more. Partly there are just many more species of arthropods. 80% of animal species are some sort of arthropod, and some lineages of arthropods are distantly related ...


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Number of legs in terrestrial vertebrates Not only mammals have four legs but actually all terrestrial vertebrates (which include mammals) have four legs. There are slight exceptions though of lineages that have lost their legs. Typically snakes have no legs anymore. Apesteguia and Zaher (2006) discuss the evolution of snakes legs reduction and report a ...


5

Remember, evolution says things don't initially develop "for a reason" -- they develop at random, non-harmful mutations are kept in the gene pool, and eventually a selection event occurs (opportunity to exploit another food source or avoid a hazard) which selects for the mutation in some subset of the population. Over the kind of timescales evolution works ...


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The main reason for bats to "develop" their echolocation system was the avalability of an almost empty niche: Hunting insects at night. Birds are not able to hunt without light and here is where the bats come in. They are able to hunt at night and also to live and orientate in environments where they are protected over the day: Caves. Bats at night are also ...


2

As canalization is defined in your question (also in wikipedia) it means robustness. Semantically it is possible to differentiate the two. Robustness of a system refers to its sensitivity to perturbations. In other words small differences in parameters would not affect the steady state of the system (parameter changes in a physically plausible range ...


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Thanks to the other answer for pointing me in the right direction with some references. It seems that two biologists in the early 1990s had a back-and-forth over this topic in The Quarterly Review of Biology.1,2 A statement of the problem: The function of menstruation is a cen tral enigma of mammalian, and especially primate, reproductive physiology. ...


0

If you are interested in this question, I highly recommend you look at the work of Jack Szostak - Nobel Prize winner at Harvard who is currently doing some of the best work in this area. His work is grounded in good experiments that point to how abiogenesis could have happened.


0

I think that it started like this: First stage: Chemicals like Na, Cl, O₂, O₃, CO₂, CO, HCN, and H₂SO₄ react to form small molecules. Second Stage: Next those small molecules react to form macromolecules. Third Stage: DNA, being the most stable was first to replicate. A membrane eventually enveloped this and formed the nucleus Fourth Stage: Via ...


5

It is a very nice question. From wikipedia: Though there is some disagreement in definitions between sources, menstruation is generally considered to be limited to primates. Overt menstruation (where there is bleeding from the uterus through the vagina) is found primarily in humans and close evolutionary relatives such as chimpanzees. It is common in ...


3

Lots of interesting questions! Let me try to address a few of them as I don't think I am qualified to answer them all but hopefully I can get this thread started. I am a graduate student in the biophysical chemistry field and have been following a little bit of the Crispr Cas9 craze in the last couple of years. So I am not an expert on Cas9 by any means but ...


0

Hansen (2006) says (middle of page 19): A link between genetic and environmental robustness is plausible, because genetic en environmental disturbances ay often affect the same functional pathways in the organism, and any increase int he robustness has been fund in studies of RNA folding (Ancel & Fontana 2000), in the effects of heat-shock proteins ...


-1

With all due respect, a few of these answers, although good examples of selection at work, were voted too high given the specific question asked: “documented examples of by evolutionary leaps being made, over the course of just a few generations?” Sometimes we’re better being honest and identifying something as an ‘unknown’ or ‘yet to be observed’ than to ...


2

You will appreciate reading this post and have a look to the wikipedia article on the evolution of aging. I make below a quick summary and apply it to your question but I think it is worth looking at the other post on aging. In short: Theory of aging Imagine a deleterious (=negative) allele (=variant of a gene) that is expressed throughout the lifetime. ...


2

Many factors have to be considered. First, although more women are delaying pregnancy until after the age of 35, the overall percentage of women doing so remains very small, as shown by this figure from this New York Times article. Only about 9% of pregnancies in the United States (for 2008) were in women over the age of 35. Most pregnancies still occur in ...


7

How did they evolve from their original form to their superficially ichthyoid appearance today? This is an example of convergent evolution. Fish appear as they do (streamlined body shape, wide tail, fins, etc.) since these are adaptations to the underwater environment they're living and evolving in. These features are only "ichthyoid" or "fishy" because ...


26

I'll focus on whales and dolphins (cetaceans) as you mention them by name and they are representative for other marine mammals such as seals or manatees. The evolution of cetaceans was one of the fascinating evolutionary mysteries. Clearly, they were mammals, but which mammals were their closest relatives? Clues to solve this mystery began to appear in the ...


3

I understand heterozygote inferiority (also underdominance or heterozygote disadvantage) as the opposite of heterozygote advantage, that is, lower fitness of the heterozygous genotype than either homozygote (as reference, see Hedrick, 2009, p. 119). I haven't seen the term structural underdominance before. However, heterozygote disadvantage can sometimes be ...


2

You seem to not understand how botulism works. It is impossible for vultures (or anybody else) to get botulism from a carcass. First, you have spores. They are ubiquitous in nature, and you have probably eaten lots of them. They are especially common on vegetables growing around/in dirt, like garlic. The spores are indestructible when using common ...


2

There are lots of parameters that influence body size. Here is a non-exhaustive list: visibility to predators ability to hunt bigger preys or to manipulate smaller preys running faster be more impressive fighting ability energy consumption for maintaining a body Quantity/quality of food to be found homothermy (heat loss) sustaining its own weight Rooms for ...


3

A dimension not explored by the other (excellent) answers has to do with color perception under trees. Leaves are green while on the tree, which tends to make mostly green light available to the understory. Viewed under green light, a green-furred animal would appear bright green, roughly the same as a white creature viewed under green light. A red or ...


2

I STRONGLY encourage to read work from the lab of Nicole King - she studies Choanoflagellates, which are the "out group" for animals - they are, in some sense, the most animal-like single celled organism that exists. Chaonos are also amazing because they go through a single to multicellular transition in there own life cycle, so they provide an amazing ...


4

Disclaimer: Not my field of research, and not a field where I know the litterature well. See it as a complement to the other answers. A distinct advantage of multicellularity is specialized functions of different cells. This can allow for higher efficiency of e.g. metabolic processes, and also that redundant functions can be removed from some cell lines, ...


5

Because of that, I assume botulinum toxin is more dangerous to humans than many animals. Couldn't find too many examples but, there are some things to consider (according to [1]): there are seven distinct types of toxin with variable action among animals different dose / effect intensity ratio between toxin types toxins A, B, E and F cause disease in ...


7

Just to add a different dimension to the answer from @Chris. Not all animal colouration is produced by melanin. A whole range of bright colours in insects, birds and reptiles comes under the heading of structural colouration, which basically involves having a repeating structure at the microscopic level to interact with light. This is the basis for macaw ...


2

I agree with other commenters that we are not necessarily living in a time of small body masses. Here is a paper on a body mass distribution. It's quite mathematical, but the first author (Aaron Clauset) is good. For individual body masses, you can look at Kleiber's law - this says that body mass and metabolism are related by a power law.


2

Everyone on earth shares a single most common recent ancestor around 3500 years ago (source), and given the vast depth of time between this ancestor and the human/chimp split it seems reasonable to assume that the number of ancestors derived via this route vastly outweighs all other ancestors so it makes sense to conclude that the difference in number of ...


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A quick back-of-the-envelope answer to the number of generations that have passed since the estimated human-chimp split would be to divide the the split, approximately 7 million years ago (Langergraber et al. 2012), by the human generation time. The human generation time can be tricky to estimate, but 20 years is often used. However, the average number is ...



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