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32

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 ...


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 ...


15

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 ...


13

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 ...


10

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 ...


9

How did multicellularity evolved? It is an ongoing field of research - Some insights about the origin of multicellularity This is a big ongoing field of research. To start with an example, there was relatively recently (2012) an important article by Ratcliff et al. that shows that yeast can quickly evolve multicellularity under selection on the speed ...


8

The technical answer is: Because the coloration of skin and hair is done by the two forms of melanin: Eumelanin, which is dark brown to black and Pheomelanin which is yellow to red. This enables colors from white (not pigmentation) to black (dense eumelanin pigmentation) and also colors in between by different ratios of the two pigments. The evolutionary ...


8

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. ...


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 ...


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 ...


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 ...


6

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 ...


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 ...


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 ...


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 ...


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, ...


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 ...


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 ...


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 ...


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

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 ...


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 ...


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 ...


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 ...


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 ...


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

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 ...


2

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 ...



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