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Short answer Blue color is not only rare in edible organisms - Blue color is rare in both the animal and plant Kingdoms in general. In animals, blue coloring is generated through structural optic light effects, and not through colored pigments. In the few blue-colored plants, the blue color is generated by blue pigment, namely anthocyanins. The reason for ...


137

I doubt we know the precise number, or even anywhere near it. But there are several well-supported theorised colonisations which might interest you and help to build up a picture of just how common it was for life to transition to land. We can also use known facts about when different evolutionary lineages diverged, along with knowledge about the earlier ...


127

First of all, let me make it clear that the heart is at the vertical centre of the body -- it is not shifted towards left (or right). However, it is slightly tilted towards the left in most cases. In some cases, it is tilted towards the right, and the condition is called Dextrocardia. For why it is so, lets look at what the heart does. Below is a diagram ...


115

Although @AliceD's answer is a great simple demonstration of the rarity of blue in our natural world, there's likely a more nuanced/technical reason. Short answer Blue light was the most available wavelength of light for early plants growing underwater, which likely led to the initial development/evolution of chlorophyll-mediated photosytems still seen in ...


102

A tiny bit of terminology Fact In popular culture, the term fact means "something that is true". I would consider a theory as being the closest concept in science to what is called a fact in the population culture. In natural sciences, the term fact is rarely used but would have the same meaning than the one in popular culture. The reason we are not often ...


97

Short answer The concept of species is poorly defined and is often misleading. The concepts of lineage and clade / monophyletic group are much more helpful. IMO, the only usefulness of this poorly defined concept that is the "species" is to have a common vocabulary for naming lineages. Note that Homo neanderthalis is sometimes (although it is rare) called ...


84

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


78

Wheels are possible on the molecular level — bacterial flagella are rotating cores inside a molecular motor, but wheels larger than the flagellum have not really been found. A single animal with a wheel is an improbable* development that would require a single animal have two separable parts (axle/wheel and body). [*read as: pretty much impossible] It'...


75

Good observation! Gene coding for the lactase Gene LCT Mammals have a gene (called LCT C/T-13910) coding for the lactase enzyme, a protein able to digest lactose. Lactose is a disaccharide sugar found in milk. Expression of LCT In mammals, the gene LCT is normally expressed (see gene expression) only early in development, when the baby feeds on his/her ...


73

Why do we age is a classical question in Evolutionary Biology. There are several things to consider when we think of how genes that cause disease, aging, and death to evolve. One explanation for the evolution of aging is the mutation accumulation (MA) hypothesis. This hypothesis by P. Medawar states that mutations causing late life deleterious (damaging) ...


70

The three "holes" are the result of the 3 carpels in coconut flowers, and three carpels is typical of the family Arecaceae (Palms). The "holes" are actually germination pores, where one is usually functional and the other two are plugged. The new coconunt shoot will emerge from the functional, open, germination pore. For further info and pictures, see this ...


70

Short answer Color-blind subjects are better at detecting color-camouflaged objects. This may give color blinds an advantage in terms of spotting hidden dangers (predators) or finding camouflaged foods. Background There are two types of red-green blindness: protanopia (red-blind) and deuteranopia (green-blind), i.e., these people miss one type of cone, ...


68

It's a matter of perspective. Most of the chemicals that are addictive to us humans (particularly alkaloids), and may be addictive for some other animals as well, are also insecticides. Lots of plants that we consider poisonous are good food for other species, and lots of plants that insects would consider poisonous are treats for us. This is a great ...


66

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 ...


55

Brian Hayes wrote a very interesting article from a mathematical point of view: http://www.americanscientist.org/issues/pub/the-invention-of-the-genetic-code especially the "Reality intrudes" section. Basically people had created fancy mathematical reasons why it has to be exactly 20. Nature, being nature, does not follow the reasoning, but has its own ...


55

There are some cases, as hinted at by the comments. But these are relatively small amount of metal. Its not that there is no metal available, but I can think of several reasons you don't see iron exoskeletons on animals all the time. Firstly, fully reduced (oxidation state 0) metal has a high energetic cost to create in reduced form. Iron is the ...


55

I think possibly the problem here is the way you're approaching the issue. You're considering improvement as anything that increases the abilities or complexity of the organism—that isn't necessarily what an improvement is though. The outcome of natural selection is that the organism best equipped to survive/reproduce in a certain environment is the most ...


55

Actually, we not only consider that all human beings belong to the same species (Homo sapiens) but even that we belong to the same subspecies (Homo sapiens sapiens). So, does it really makes sense? Concept of species First, please note that the concept of species is more arbitrary than the most layman would think. I wrote my opinion about the concept of ...


51

Richard's answer is fantastic, and I'm not going to be as thorough. But here's some other examples: Turtles (which did sea to land to sea back to land!) Gastropoda (snails and slugs) Tardigrada (water bears) Onychophora (velvet worms) Planaria (flatworms) Annelida (annelid worms) Together with Richard's examples that includes all the examples of ...


48

Birds are both flying dinosaurs and flying reptiles. Yes, that's potentially confusing. To understand the apparent contradiction, you have to understand how modern classification of organisms works (phylogenetic systematics). Under the old (Linnean) classification system, Reptilia (reptiles) was an order and Aves (birds) was a separate order. Phylogenetic ...


47

Short answer Early sea water had a very different osmolality than blood plasma. Background The reference range of serum osmolality is 275–295 mosm/kg (mmol/kg) (MedScape). The osmolarity of sea water is about 1000 mOsm/l (Wikipedia), but it can vary substantially between different seas, namely between 642 and 1,480 mOsm/kg (Ninawe & Banik, 1998). ...


43

Take a look at this little fellow: It's a flying squirrel — a shy little nocturnal rodent which lives in trees and, despite its name, does not actually fly. It does, however, have a skin membrane called a patagium between its fore and hind limbs which allows it to glide from tree to tree and thus evade ground predators. It's not hard to see how the ...


42

First, a note on spelling. Both "ortholog" and "orthologue" are correct, one is the American and the other the British spelling. The same is true for homolog and paralog. On to the biology. Homology is the blanket term, both ortho- and paralogs are homologs. So, when in doubt use "homologs". However: Orthologs are homologous genes that are the result of a ...


42

This entire answer will be long, so read the short part first, then read the rest if you (or anyone else) is curious. Citations are included in the long section. I can include additional citations in the short section if needed. Long Story Short Your question touches on some common misconceptions about how the evolutionary process. Organisms don't "want" ...


38

There are 5 answers, all "yes" (though the first one is disputable). First: there exists at least one animal which can produce its own chlorophyll: A green sea slug appears to be part animal, part plant. It's the first critter discovered to produce the plant pigment chlorophyll. The sea slugs live in salt marshes in New England and Canada. In ...


37

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 ...


37

I found many plausible claims that fingerprints increase friction. However, the following article claims, at least under their experimental conditions, that fingerprints actually decrease friction with smooth surfaces by reducing contact area. Fingerprints are unlikely to increase the friction of primate fingerpads. It is generally assumed that ...


37

Short answer Shedding or reabsorbing the endometrial lining is energetically advantageous to the female.The advantage of shedding over re-absorption may be that sperm-born pathogens are removed from the uterus. A more parsimonious explanation, however, is that the endometrium in primates has developed into too large of a structure to be completely reabsorbed ...


37

Going through the possible answers (A) Rates tend to be very high in most populations. This is a very unclear statement. What does "high" mean? In humans, the average mutation rate per reproduction per nucleotide is of the order of $10^{-8}$ (Rahbari et al., 2016) (hence of the order of 10 - 100 mutations for the whole genome). Whether someone wants to ...


36

but I get lost on the 'border' cases. Not surprisingly, since there are no borders, and this is probably the greatest misunderstanding: Evolution is gradual. It’s not generally possible to say where a complex feature (or a species) starts and another one ends. We could in theory say, for individual mutations on the genetic level, in which generation they ...


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