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14

Determining why one species (or group of species survived) while others did not can be difficult to answer, but I can offer one possible explanation for the genus Homo: competition. Competition between similar species is one possibility. Consider for example gorillas or chimps. The two species of gorillas occupy different habitats so they rarely compete with ...


8

Definitions of adaptation Unfortunately, there is not such thing as a single, standard definition of adaptation. But for most cases the accurate definition the author is using is not of much importance as all of the usual definitions totally fit in the sentence without changing the meaning of the concept they want to express. In you case however, the ...


8

This is a common misconception about evolution, many skeptics ask something along the lines of "If humans evolved from monkeys, why are there still monkeys?" The answer is that evolution is not a linear process of one species becoming the next species becoming the next. Species branch off much more like a tree. At some point in the past the last common ...


6

The woman running bit is obviously a myth but that is genius.. Other than that the length of the umbilical cord has been found to be highly variable depending on each individual. Characterizing it as just long would therefore not be right. According to Wikipedia, The umbilical cord in a full term neonate is usually about 50 centimeters (20 in) long ...


5

Yes, there are examples. First: If you want to say, that humans and monkeys evolved, than it is better to say that they evolved from a common ancestor. This makes quite a difference. If you are looking for examples of human evolution then one of the most obvious traits under evolutionary selection is pigmentation. There is a clear correlation with lattitude ...


5

Your questions mean basically the same. Birdcare.com says: The situation in which all the eggs in a clutch do not hatch at (more or less) the same time, as is more usual among birds, but have their hatching spread over several days. It is well seen in the various types of raptor, and is an adaptation to a type of food supply which may fluctuate. During ...


5

Howe and Smallwood (1982) provide a nice review of the many methods of seed dispersal that have evolved in plants. The review is broad but they do have a section on frugivory. They highlight hypotheses developed by McKey, and Howe and Estabrook (see Howe and Smallwood for citations) that suggest plants may use one of two strategies. One strategy is the ...


5

There are two aspects to your question. First, organisms have some kind of symmetry. The field of evolutionary developmental biology has some theories on why our anatomy is the way that it is. So, we have two eyes, two halves of our nose and two nostrils, one "tube" that becomes the path from our mouth to anus, etc. Our nostrils are just part of that ...


5

Oxygen levels have changed greatly throughout Earths's history starting with very little atmospheric oxygen and gradually increasing as photosynthetic activity appeared until all the oxygen sinks such as minerals had been filled, then taking off, reaching as high as 35% of the atmosphere during the carboniferous period 3. The reasons behind this sudden ...


4

These equations describe how the haplotype frequencies will change over time due to a combination of recombination and natural selection. Before I proceed, I need to change your four $\delta X_i$ formulas above. Lewontin and Kojima (1960) writes the equations as: $$\Delta X_i = \frac{X_i(w_i - \bar w) \pm Drw_{14}}{\bar w}$$ where the minus sign is used ...


4

The urogenital system as a cohesive functional unit probably evolved very early in vertebrate history. Hagfishes and lampreys have separate systems for reproduction and excretion. More derived groups of fishes use kidney tubules and ducts for sperm delivery outside the body (Helfman et al. 2009). The vertebrate nephron may be homologous to the invertebrate ...


4

According to the link you provided, the phenomenon Haidinger's Brush seems to be associated with the macula of the retina. The yellow color of the macula may explain the yellowness of Haidinger's Brush. This suggests to me that the brush may be an artifact of the structure of the eye, and others have claimed that Haidinger's brushes probably do not have any ...


4

A trait is said to be adaptive when it causes fitness to increase. Fitness is generally understood as the (relative) contribution to future generations in terms of offspring or genes. The trait is selected for by the environment and hence increases fitness. In the paper of Dey et al. this is the fitness of the parent birds. Hatching asynchrony causes size ...


4

First: Not everything what happens in biology is necessarily directly selected for. Sweating is of course selected for, so our body can maintain its normal body temperature in hot climates. There is a difference between sweat glands under our armpits and for example on the forearm. Under our armpits we have the so called "apocrine sweat glands" while most ...


3

There may be an evolutionary purpose to underarm perspiration, as alluded to in the "hidden hint" link of @DevashishDas, and also hinted at by the answer by @Chris. The apocrine sweat glands of our armpits produce steroids. One group of steroids secreted by the axillary apocrine glands are sex pheromones. Although we may not consciously notice the chemical ...


3

If you're interested in learning about the mathematics of population genetics, Population Genetics and Microevolutionary Theory by Alan Templeton is an absolutely amazing resource. If you check out the index, here are entries under population structure: assortative mating, admixture, linkage disequilibrium, coarse-grained spatial heterogeneity, gene flow, ...


3

This book "A primer of conservation genetics" would suit quite well I think. In particular chapter five deals with "Genetics and Extinction" and is preceded by a lot of population genetics based theory. A beginner might also combine it with "A primer of ecological genetics" (Hartl & Conner) but you seem to have enough Pop gen knowledge to not need it! ...


3

As the previous answers clarify, all organisms have heritable traits that may be manipulated through selective breeding. It is the pragmatics that can be prohibitively challenging. From an (zoo)archaeological point of view, few animals have actually been domesticated, and only recently in our species' history. The dog is an unusual case, perhaps domesticated ...


3

We have two nostrils for the same reason we have 2 ears and 2 eyes. Having 2 nostrils means an odor molecule coming from one direction will have higher concentration in one nostril than the other, so we can determine what direction the smell is coming from, and allows us to find food or avoid predators more effectively. While humans no longer rely on smell ...


2

The two amoxycillin formulations you mention pair the amoxycillin with a Beta lactamase inhibitor. This is because of the prevalence of resistance to beta lactam drugs including amoxycillin. If we were to invent a brand new never before seen beta lactam drug and started using it irresponsibly, there would probably be resistant bacteria within 5 years. The ...


2

The answer provided by @MCM contains an important chunk of information (Bioluminescence!) but it does not answer the question entirely. First, let's correct a misunderstanding in the question. Sunlight does penetrate beyond 200m in the ocean. The intensity is not enough for photosynthesis to occur (and thus no phytoplankton below 200m) but depths between ...


2

It depends on how different. Day length affects more than just how long the periods of light and dark are. Let's assume a very slow rotation, and a very long day, maybe 1 month light, 1 month dark. The light side would get much warmer while the dark side would get much cooler. At the border between light and dark sides, you'd expect to see powerful storms as ...


2

Not relatively short, but I'm going to repeat a recommendation I just made in another thread. Population Genetics and Microevolutionary Theory by Alan Templeton covers many of the topics listed above, and is heavy on the self-learning of various population structure statistics, with examples. It is an introductory textbook with for people with some ...


2

I think Wallace (1968) developed the ideas of hard and soft selection, as they relate to genetic load. He further explains the concept in Wallace (1975). As the idea was his, I'd go with Wallace's definition over Whitlock's. I haven't had time to watch the Whitlock video to see if they are saying more or less the same thing overall. Consider a hypothetical ...


2

As everybody, I don't fully understand your question. Can you please add your definition of domestication? Would you consider domestication as soon as human can select for heritable traits? If yes, then the question may be split in two: Do all animal populations have heritable traits? Yes! But Depending on what kind of traits you want to consider no ...


2

Welcome to BiologyBeta.SE! On stackExchange sites, an OP should always limit his/her post to one question and should make his/her question is not too broad. But before you split up your question I invite you to have a look to some other post that will give you some answers. For this reason your question will very likely get closed as too broad. But I am ...


2

I think other answers have explained natural selection, but I think it is also important to note that species boundaries are applied in retrospect. This sounds blindingly obvious, but when presented by skulls from two species, such as Homo erectus and Homo sapiens, many will then ask where the evidence is for the species that came between those two. There ...


2

Lactase persistance is evidence of recent and ongoing natural selection in humans. Mammalian young produce lactase, an enzyme needed to break down the lactose sugar in the mother's milk. The young quit producing lactase after they are weaned because they no longer drink milk. Most humans (roughly 70%) also quit producing lactase when they are young. Without ...


1

If all early forms of humans are gone, is it because the more modern humans had a greater evolutionary advantage? If you take an environment where species dwell, three things could have happened: The population got smaller and smaller, in a given environment, and then bam the last ones disappeared without producing any offspring. This is because ...


1

Armpit sweat does not have a strong intrinsic odor. What you smell is the waste of the microorganisms which colonize your armpits. It is a similar mechanism responsible for foot odor and bad breath. All external bodily surfaces have particular microbes which prefer different areas. This also includes the intestinal, oral and nasal regions. If you charted ...



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