As an aside the blue whale is approx 90 ft long, and recorded as the largest animal in history. Beached whales frequently suffocate as their body weight crushes their respiratory system without the buoyancy of water. This would imply the maximum size for a land animal must be significantly smaller.
Posts by Phil Leftwich
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Technically the definition of species is one in which the members cannot interbreed with members of a different species. So organisms within the same genus should not be able to interbreed.
This has some wiggle room depending on certain definitions. For instance two organisms might be from different species if they do not interbreed in the wild, for instance if they occupy completely distinct geographical areas, or if they do not recognise each other as mates. However in an artificial setting or through IVF it might be possible to produce offspring, but the species definition is intact if it doesnt happen naturally. The species definition is also still intact if organisms can reproduce but produce infertile offspring.
Problems arise because the species definition is somewhat abitrary, as many organisms are on what could be deemed a spectrum of speciation whereby some populations reproduce between each other but do so rarely, or when they do hybrid depression (where the offspring is less fit than either parent), means there is a selective advantage to not interbreeding. So that in reality animals often have to be studied on a case by case basis.
Short answer no, or at least I don't think so. The genomics of speciation is an up and coming field of research, but one which is not fully characterised as yet.
The number and size of chromosomes is an easy place to start, however while chromosome number disparity means hybridisation is unlikely, it may not be impossible, and First generation sterile offspring are produced in a number of chromosome mismatched hybridisations. For plants, even this is not much of a barrier.
However even if the number of chromosomes appeared to match perfectly, without a full genome sequence you don't know what genes they are carrying (or whether there have been any gene translocation events, chromosomal inversions that prevent genes aligning etc). Producing a whole genome sequence is no easy task, and most organisms are still unsequenced. Even if you have a full genome, the function of each gene will likely be unknown without characterisation studies. At this point you will have no idea whicg genes may be important to reproduction.
Barriers to hybridisation can pop up at any point along the route towards reproduction and while the ultimate cause of these is usually genetic they can work at different stages, animals not recognising each other as mates, genitals which do not fit together, changes to the chemical cues such that sperm do not recognise egg or vice versa.
Speciation is a fascinating area of research by looking at partially fertile hybridisations we can look at speciation in action, but at the moment we are very much at the stage of trying to understand how barriers to hybridisation occur and what they might look like at the genetic level, only when we understand these processes can we start to make accurate predictions
The link between mutation and natural selection is firmly established, and indeed small mutations in the genetic code arise occasionally, most happen in "non-coding" DNA, parts of the genome which do not get translated into proteins, and therefore mutations can occur which have no effect on changing the organism whatsoever. More rarely mutations occur in coding DNA, where the changes translate into a change in the shape of a protein, this can, depending on the circumstances be beneficial or harmful to the organism, and is where natural selection acts.
As for the causes of mutations in the genetic code, these generally arise from copying errors as cells divide, when this happens in sperm or eggs they can be passed on to offspring, external factors such as radiation can increase the rate of mutation by damaging DNA beyond the cell's ability to repair, but mutation is mostly an internal issue. Therefore to your second point, the rate of mutation between different organisms can be startlingly different.
Some, in brief, reasons then why some organisms remain the same over millions of years:
1) these are exceptions and not the norm, and almost always occur in very isolated, stable, environmental niches, such as the deep sea or large cave systems. A stable unchanging environment removes natural selection as a drving force.
2) These are often fairly long-lived organisms, the longer it takes each generation to pass, the slower the rate of evolution.
3) small population sizes, small populations equals a smaller number of mutations occuring
4) Quirks of biology such as eluded to before, a lower than average mutation rate, or developmental constraints
5) They have changed we just can't see it! We can see evolutionary changes in "non-coding" DNA, it is frequently used in evolutionary studies to build up evolutionary trees of relatedness or cladograms. These show evidence of changes between species without there being visible effects. Changes can occur in these regions of the DNA, or in internal cellular proteins, or in features such as hair colour or scale colour which are evolutionary changes, but are not preserved in the fossil record.
The confusion here stems from a misconception of the process of mutation and natural selection. Evolution is not a guided process and animals do not develope mutations to suit a need. Mutations happen regardless of "need" and most are incredibly harmful, think of the many genetic diseases in humans. However very occasionally mutations occur which can confer a small advantage to an organism, natural selection is then the name given to the process by which those organisms which have traits that improve their survival leave more offspring on average than other members of the same species. It is the steady accumulation of small mutations coupled with natural selection which removes bad mutations (organisms carrying those mutated genes die or leave fewer offspring), while selecting for beneficial mutations, that eventually leads to the development of complex traits that benefit the organism.
Oh and it's not true to say that the statement is unfalsifiable as long as we can make predictions as to the levels or sustainability of simultaneous selfish and altruistic behaviours in populations, or when it would be most rewarding to pick one behaviour over another.
Game theory (mathematical models that are used to help predict and explain animal behaviours and the evolution thereof), allows for and usually expects a mixture of selfish and helping behaviours within any society, simplistically it allows for the majority to behave altruistically for the common good but will always be vulnerable to and carry a certain number of selfish individuals. Or more likely it allows individuals to be mostly altruistic but occasionally manipulative and selfish.
Broadly speaking we have allopatry and sympatry as the main types of speciation. Allopatry (as mentioned above) occur when geographical barriers separate two groups of the same species. Now new mutations can arise, either through Natural selection or Genetic drift, which eventually change the populations enough that we now recognise them as separate species, and were we to put these two groups back together there would have been enough mutational differences between them to prevent hybridisation (this can come in many forms, pre-zygotic the organisms do not recognise each other as potential mates, there reproductive organs do not fit or gamete incompatiblity or post-zygotic, the hybrid offspring are not as "fit" as either of their parents).
The other type of speciation, sympatry is where the mutation preventing or reducing gene flow occurs first. For instance a new mutation which increases your likelihood of mating with someone else carrying the same mutant gene, over time this can create two new reproductively isolated species that occupy the same geographical area.
To find out more try googling some of the terminology I have listed above, it should produce articles detailing them in greater detail. And feel free to come back with more questions!
An interesting question which has been debated on here before, check out this thread
I think this is a misunderstanding stemming from what a 'mitochondrial eve' actually means. Your summary of evolution is a simple but correct analysis of how speciation often occurs, i.e. that it works on populations, not individuals. The only reason mitochondrial eve throws an 'apparent' spanner in the works is because mitochondria are only ever inherited maternally. Now try and visual that, it means that whenever a woman has sons her mitochondrial lineage stops with them, and goes no further, it is only passed on through her daughters. As such probability dictates that certain genetically distinct forms of a mitochondria will go extinct over successive generations, so that at ANY TIME there will always be a mitochondrial eve and arbitrary amount of time ago, move back to when our mitochondrial eve was alive and there would have been lots of other humans around some with the same mitochondria as 'eve' and others with other variants that went extinct in the intervening timespan, nevertheless all of these humans would be able to trace their mitochondria back to their own 'eve' etc.
It is a slightly confusing topic, but it means that having a mitochondrial eve tells us nothing about the population size at the time, relative amounts of genetic diversity at the time or anything like that, because it has nothing to do with nuclear DNA or normal inheritance.
And yet, increasing female age is more readily associated with the increased risk of developmental abnormalities, while there is a similar risk with older fathers it is nowhere near as strong, which would indicate that risk of mutations occuring through ageing is not primarily responsible for the difference between inheritance of mutation patterns.
I think a more likely explanation comes from the fact that while men are constantly undergoing spermatogenesis, women produce all of their eggs during foetal development, at which point there may be over a million eggs. However during early life and adolescence the number of eggs falls to the region of tens of thousands, which is believed to be primarily the result of a form of screening for abnormalities, the result of which is fewer spontaneous mutations survive into functioning gametes.
I'm not sure I totally agree with that advice, biochemistry is a pretty specialised degree route. My Zoology degree by comparison covered molecular biology and cellular biology through to evolution, animal behaviour and conservation biology. I would suggest finding out what the actual modules in each course will cover over the 3/4 years and deciding from there, based on the breadth of topics but much more importantly what sounds interesting to you, because you are the one who will have to study it in depth for several years
There have been several questions on this before so I suggest you check out these answers below
It is only honeybees in the UK which have barbed stingers, so bumblebees for instance can sting multiply without losing their stinger. There has been some discussion as to whether barbs originally evolved to help stingers gouge into exoskeletons i.e. be used in bee vs. bee assaults.
If a honeybee stings a mammal, the comparitively elastic skin means that when the bee tries to pull away it's stinger becomes embedded and the lower abdomen tears away from the bee. This is not unique to humans and will occur if a bee attempts to sting any mammal.
If the demands being placed on the cells in terms of energy production are not increasing, then the cellular rate of respiration will not increase. (You breathe heavily when running because the muscles in your body have increased their respiration rate as they are working harder to move the muscles, as such they require more oxygen and your breathing rate increases to compensate) Breathing heavily might increase the respiration rate of the muscles directly required to increase the breathing rate, but according to this piece of information, the increased heat generated is clearly more than overcompensated by the cooling effect by water evaporation.
You have touched upon an interesting topic known as extra pair copulations. Essentially it is with the advent of new molecular technologies that biologists are really starting to be able to detect the levels of promiscuity in certain mating systems.
Any male bird will produce more sperm than a female could possibly need to fertilise her eggs, however many species of birds have been shown to lay clutches of eggs with multiple paternties. Why would a female do this? Well there is mounting evidence that this can improve a females 'fitness', and this can occur in several different but potentially co-occuring ways. Multiple paternities ensure wider genetic diversity of her offspring and if disease struck she might not lose all of her children (think spread betting in gambling). Confusing paternity might encourage parental involvement from both fathers, or alternatively a female may simply mate with a first male to ensure she has offspring and then mate again with a 'better' or more compatible male later. Alternatively a female may simply mate with as many males as possible and let the best sperm win (know as cryptic female choice), rather than attemtping to judge the quality of a male before mating.
All of these processes have been shown to occur in birds, different species have evolved different mating strategies, each one an attempt to make sure the female has as many healthy offspring as possible.
With regards point 1 from Alistair, I assumed it was written by a lolcat.
Well I can't speak for all species of maggots, but the mediterranean fruit fly that I work on, certainly doesn't burrow straight into the core of the fruit. It spends most of the initial larval development just underneath the skin of the fruit, before burrowing deeper into the flesh, and certainly doesn't beeline towards the core.
Of course any maggot which does go the centre of a fruit rather than the edge may be safer of course than one on the edge, from accidentally climbing out of the fruit, being eaten by a larger animal eating the fruit or from being crushed if the fruit falls from the tree.
A platypus is a montreme, which along with the echidna are one of the few remaining species of this ancient group of mammals. They have a different common ancestor to all the other mammals, and are evolutionarily and physiologically very distinct to other mammals. As mentioned above they lay eggs rather than give birth lo live young, and the term monotreme describes the fact that they have a single posterior opening (cloaca), through which the reproductive tract, urethra and anus are all connected. This is the same morphology as reptiles and birds, hence the potential for confusion.
I recommend Seven Deadly Colours by Andrew Parker, a whole book dedicated to colour, vision and evolutionary biology. As humans we have three colour receptors, or trichromatic colour vision, and we interpret all wavelenghts of light in relation to how close they are to the peak sensitivity of each of these three cokour receptors. Most other mammals are dichromatic and so have less sensitive colour vision (believed to be a hangover from our nocturnal evolution where colour vision was less important than resolution in low light, primates re-evolved colour vision probably to better detect ripe fruit in canopies)
Bees are also trichromatic, but more sensitive in the ultraviolet spectrum, which means they can see hidden patterns in flowers but are unable to see a red light if you shine it at them.
Other organisms have many more colour receptors and will see the world in colours we cannot imagine, many butterflies are pentachromatic, and one species of shrimp has 12 colour receptors!
I'm not sure it does, Australopithecus is a hominid, and probably one of our ancestor species, but it was already bipedal and is estimated at 1.8-4 million years old. The earliest divergence of humans from chimapnzees is thought to be around 5 million years ago.
There are several fossil species which have been identified as members of the hominidae which may have been the ancestral species of the great apes and humans including Ouranopithecus and Nakalipithecus.
Obviously the fossil records are fairly sparse so it is possible that the particular species which is the common ancestor of humans and chimps may not have been found. The best we can currently say is that these species are the right age and we can infer from their morphology that they are at least a sister species to our common ancestor if nothing else and allow us to make several insights into our evolution.
Agree with everything David has said above, however there are intrepid scientists involved in origins of life research, the forerunner idea being that the first single celled life may have evolved out of replicating molecules in the deep sea smokers. Very, very difficult conditions to attempt to reproduce, but some people are trying, like DrLane at UCL
In most instances human love is directed to those who we are related to and those we are in a sexual relationship with. From an evolutionary viewpoint it is good to be highly invested in their wellbeing as it strongly impacts on our own 'fitness'.
A caring and loving attitude towards our siblings is beneficial because of a process called kin selection. Our siblings carry genetic material that is 50% identical to our own, therefore helping our siblings helps our own genes thrive.
There is even an equation to accompany this, known as Hamiltons rule where it is beneficial to help someone you are related to if it results in an increase in the number of offspring they have, as long as it is not more costly to you in terms of a loss in the number of offspring you have. In real terms this means that every niece and nephew you get from your brother and sister increases your fitness, but only half as much as having a child of your own. Therefore you want to help, but not too much. I.e. you will love your brother and sister, and their nephews and nieces but not as much as your own child. (you are the same relatedness to your child as your brother and sister, but the child is from the next generation and therefore represents a direct passing on of genetic material)
Actually sorry, I have been meaning to get around to answering this question for a while, the reason we have a MCRA for X and Y chromosomes which can be traced back to a single person, is simply an artefact of the fact that such inheritance patterns can only travel from mother to daughter or father to son. This asymmetric pattern of inheritance means that it actually tells us nothing about population sizes or bottlenecks. And the genetic diversity of the rest of the human genome bears no relation to the sex chromosomes.
With regards your first point, how can single celled life, reproducing asexually evolve into muticellular life.
The best scientific explanation behind the origins of life that I have read are described by Nick Lane http://www.nick-lane.net/ in his book Life Ascending. In it he details the conditions under which the first life probably evolved within 'hot smokers' found in deep sea trenches. It is the jump from this to the first single celled organisms which is currently being hotly discussed and experimentally tested.
The movement from single celled to multicellular life by comparison is a far less controversial topic. For instance although single celled organisms reproduce asexually, sex is not the originator of evolution, it allows recombination of genetic material so that new variations can occur, but it is genetic mutation which provides the raw material for natural selection to work on. Any cellular division occasionally produces mutations and so single celled life is perfectly capable of evolving (usually at a substantially faster rate than multicellular life).
Additionally most bacteria are capable of conjugation, a process whereby two bacterial cells can swap genetic material, this allows beneficial genes such as those conferring antibiotic resistance to spread rapidly.
As for the evolution of multicellularity, being multicellular can have several advantages, less able to be eaten by predators, greater control of movement, cell specialisation. And this process almost certainly started when a cell divided but remained clumped together, natural selection would then drive this forwards. In fact we have living species today that occupy every step from single celled life, simple multi-cellulars like sponges, simple body plans and cell specialisations like the hydra and more complex multicellulars like flatworms and finally ourselves and other animals.
Sex would have evolved after multicellularity, from conjugation, to simple gametes where there are no sexes, until a process called anisogamy drove the differentiation of gametes and finally the evolution of fixed sexes. Again there are many organisms alive today which show how this process would have developed.
The second point has been addressed by my colleagues, but I will say that the 'evolution is a theory' argument is tired and old. Despite the semantics, evolution is both a fact and a scientific theory, it is experimentally observable, verifiable and repeatable.
Darwin published his book over 150 years ago, and we have come a long way since then, it really doesnt matter that he couldn't answer questions about the origin of life. Modern biologists do not cling to his tenets, rather appreciate his contributions to mdoern science and recognise his work as of its time.
So generally when introduced to the concept of population genetics we are taught about the Hardy-Weinburg Equilibrium, which states that withouth natural selection, allele frequencies should stay the same from one generation to the next. However, as with many concepts, its often a little bit more complicated in real life!
The phenomena you are referring to is genetic drift. Whereby the frequency of a particular allele in a population changes over time, despite not being positively or negatively selected. It is all down to probability, while any one neutral allele that arises by mutation is very unlikely to spread through a population, occasionally one might.
One reason for this is linkage disequilibrium, in HW we are taught to think about genes as discrete packets, however in reality genes on the same chromosome have a statistical likelihood of being inherited together dependant on their distance from one another. Put simply, a neutral gene may be inherited preferentially simply by being situated close to an advantageous gene.
Other reasons may be due to founder effects or population bottlenecks, if a population shrinks suddenly then genetic variation is reduced and a 'lucky' neutral gene which survives is suddenly at a much higher frequency, not through an increase in its own copy number, but a decrease in all the other alleles.
And of course a gene can always just be 'lucky', while it is statistically unlikely that a rare gene will increase in frequency randomly, this does not make it impossible, and as such very occasionally a gene will do just that, simply by happening to be in organisms which have had a slightly greater survival or fecundity rate through nothing more than luck, if this trend continued over several generations then the gene frequency goes up. In fact by calculating mutation rates and likelihoods of new mutations reaching fixation, it is possible to use genetic drift as a 'genetic clock' for studying population genetics.
This is a question which has been asked on the site before, check out these answers and see if these answer your questions. :)
Yes they do, and just like in bees, she will invariably do almost all of the egg laying, while her daughter workers look after the nest.
You have stumbled across a whole section of sexual selection, there are many reasons why a female might mate multiply and this will depend heavily on the type of animal and its mating system.
The reason females tend to benefit less from multiple matings is rooted in Bateman's principle, which proposes that as females 'tend' to invest more energy in reproduction than males, that they should be more choosy about who they mate with and mate less overall.
However, there are important caveats to this, and it has been show many times that females should and do receive fitness benefits from mating with multiple males, even if it is less pronounced than the amount of mutlipe matings males can achieve.
The reasons for this are multiple but a few of the more important ones are 1) one male may not be sufficient to fertilise all of a females eggs, females have been show to mate a higher frequency when male sperm quality or numbers are low 2) cryptic female choice, females may choose the 'best' male after copulation. Either through an active process or through sperm competition. Gametes from multiple males may be held in the female reproductive tract (most often in insects) before being exposed to the females eggs and the 'best' male may fertilise more eggs than the the other males. Essentially this is the same as a female choosing which male to mate with, but the choice happens post-copulatory rather than pre-copulatory. 3) genetic variation, by having post-copulatory selection, one male may fertilise more of the eggs than the other males a female has mated with but there will still be a multi-paternal brood (obviously only in those species where this is possible i.e. multiple births) which can lead to greater genetic variation in the females offspring. 4) an inbreeding avoidance mechanism see this good recent example from Science http://www.bbc.co.uk/news/science-environment-15002277
Hopefully these examples should start to explain why and how multiple mating in females has evolved.
All the mosquitoes are Diptera, so should be regarded as true flies that feed on animals and humans, and there's a lot of those around. But remember its only the females that feed on blood, the males prefer nectar!
Okay well fraternal twins are formed when two eggs are fertilised by two separate sperm and implant into the womb at the same time. Genetically there is no more similarity between fraternal (or sororal, or more universally dizygotic) twins than between any other brother and sister. Similarities may be more apparent simply because they are exactly the same age, however like any siblings they may appear very similar or rather dissimilar through random chance.
Monozygotic or identical twins are genetically identical, however the expression of these genes and the resulting appearance of a person is strongly influenced by the environment.
Freckling is a good example of this, the presence of freckles is strongly influenced by genetics, however where they appear can be fairly random, additionally effects such as sun exposure can induce freckling etc.
This is is a questuion that has been asked before
Evolution is a change in a species over time, this is driven by natural selcetion pressures as well as and perhaps more importantly genetic drift over time. There is no reason to think that we have stopped these processes at all.
Arguably our advanced brains has developed a certain cultural evolution which develops at a faster rate than our biology, and may have a large impact on our physical evolution, but we have not transcended evolution even if we are affecting how we evolve. By definition of being a living organism I think we are incapable of not undergoing evolution.
Ok well assuming that this isn't simply some random effect of development (not everything is always genetically pre-determined) i.e. it could be due to levels of certain growth hormone levels experienced during pregnancy, there is some evidence that finger middle to ring finger ratios in humans can be influenced by levels of testosterone exposure during development, I do not know if the same applies to toes!
On top of this many traits are controlled by multiple genes all working in concert. Your son is a unique combination of some of your and some your partner's genes and which combined have created a unique individual. He will invariably have traits that neither you or your partner have, such as a longer middle toe.
Alternatively a simple explanation could be that 'long middle toe' is some sort of recessive trait, everyone has two copies of each gene, one from their father, one from their mother. If your partner had one recessive big middle toe (BMT) gene and one dominant little middle toe (lmt) gene then he will expre a little middle toe. As his partner has a big middle toe she would have had two copies of BMT. And there was a 50/50 chance of having a child with a big middle toe, depending on which gene they get from dad. If we assume that you, like your partner have one copy of each gene, then you had a 1 in 4 chance of having a child with a big middle toe!
Unfortunately I don't know which of these answers is correct, they are all distinct possibilites. And genetics is a complicated thing, but recessive genes are very common, and they are only expressed when a child is born to two parents that BOTH have a copy of that gene.
So I'm going to go out on a limb here and say that this was probably some kind of social wasp, i.e. one that lives in a nest as a worker with many others, rather than a solitary wasp. This is because most solitary wasps are parasites as larvae, developing inside an unlucky host. However some social wasps will have larvae developing inside constructed nests and the workers will provision them with meat.
An adult wasp will drink only nectar, those mandibles you see are for attacking other insects, defending hives etc. and they also enable the wasp to cut up chunks of meat which it can take back to the hive to provision the young larvae with fresh meat!
In some cases the larvae will even provide secretions from their bodies which provide the adults with food. So that the adults can be being fed (albeit indirectly) from any carrion they bring back to the nest.
Hope that answers everything!
Yes you are correct, the issue is making it clear that we did not evolve directly from any existing species of apes, rather we and they have both evolved equally far from a common species, which would by any taxonomist, be classed as a type of ape. But might for clarity be described as a prehistoric ape.
Common sense dictates that as chimpanzees are more closely related to us than any other species of ape, that the basic body structure of 'the ape' must have evolved before the human/chimp lineage split off from the rest of the apes, and therefore obviously before humans evolved as a separate species.
Some fossils Nakalipithecus nakayamai have been found of a prehistoric ape, which is believed to be the a common ancestor of humans, chimps and gorillas. It has been placed firmly in the Primate Order.
And just to bring the topic onto sex, the largest sperm cell in the world is about 5.8cm long, making it 1000 times larger than a human sperm, and it's found in Drosophila bifurca, a tiny fruit fly which has a body size of just a few mm. The sperm is intensely coiled in order to fit inside the fruit fly! So in this case the relationship is completely inverse.
First off, this is not a debate forum, so this will not continue as an argument, however I will answer briefly your points.
First, you are correct, birds have offspring that are also birds. No species does in the instant of a single generation produce a different species. This is not what evolution predicts, rather an entire population can change over thousands of generations via the accumulation of mutiple errors caused by mutation, which are subsequently acted upon by natural selection. If you wish for more details on these I suggest you find some standard biology/evolution textbooks and ask back here if you have genuine questions about particular aspects. We are volunteers and therefore have the time to answer brief questions, not the hours and hours it would take to provide a detailed breakdown of the current understanding of evolution, bottom up.
However, there are plenty of examples of transitional fossils, many more are being found all the time a case in point being the Archaeopteryx-like theropod recently found in China. Also genes most certainly change, new mutations can and are found all the time, this is easily verifiable by genetic sequencing. Every human being is born with new mutations in their genetic code, which can be confirmed by genome sequencing, new altered genes in you which cannot be found in either parent.
Finally with regards to organs, yes all extant organisms have fully functioning organs, otherwise they wouldnt exist, however the function of these organs can and has changed over time, also easily verifiable via the fossil record and comparison between closely related species. The eye is a good example, we now have a very confident idea of how the complex eye evolved from photosensitive receptor cells, through to a concave pinhole style camera followed by membrane formation of the cornea etc. pieced together from 'simple' extant and extinct organisms. At each stage it was complete and functioning, but it has been 'improved' as natural selection drove the selection of organisms with the best visual acuity.
Evolution continues to be supported by an overwhelming body of evidence, I suggest you start reading up on it, it is after all the story of life, and it's pretty cool!
So basically, if we use your example of bigger noses being sexually selected, then yes, noses will get bigger throughout the population. However there are two traits being selected for here, those males with bigger noses and also a female preference for males with bigger noses. Those females which are able to utilise the fact that bigger noses on males represent greater virility also gain a fitness benefit. As such while male noses get bigger, female preference for big noses also gets stronger. This is a situation known as runaway sexual selection, where the preference and trait both get more pronounced like the situation of the peacocks tail where male's have a highly exaggerated sexual ornamement.
Of course this situation relies on the trait being able to become so exaggerated, it would be unlikely that a nose would ever grow to elaborate proportions, given the natural selection disadvantages it would accrue which would far outstrip any sexual selection advanatges, so every trait will have some inbuilt limit at which it cannot become more exaggerated. At this limit, there will be a considerable energy cost to development of this ornament, and only the healthiest and fittest males will be able to produce it. Studies have shown that many bird's sexual ornaments are reliable indicators of their parasite load etc. allowing females to discriminate between males with good health and strong genes etc.
In humans the there is less sexual dimorphism, and this is a sign that sexual selection is weaker, it is a sign that our mating strategies probably rarely involved one alpha male with access to all the females, and may have been more likely monagamous pairings or perhaps more polyamarous grouping like the bonobo chimps. In these situations, sexual dimorphism is usually weaker as there is less intense competition between males for mates.
Ha! I don't think I'd got around to having some coffee yet when I wrote this.
A seed is most definitely alive, it contains
the living embryo (which is dormant, where metabolic activity is
severely reduced, but importantly not stopped completely) of a new plant
and a food reserve
So cellular activity may be reduced, but is still occurring. That is why seeds do not last forever, keep a seed out of the ground for long enough and it will die and no longer be able to germinate, only when the right conditions occur does it germinate.
The point is that a seed is capable of all the above under the right conditions (though not evolution, no organism evolves in a single lifetime, rather it occurs over successive generations), in the same way that you or I are only capable of such things under the right conditions, we do not feed constantly but intermittently, we can only reproduce when a member of the opposite species is available.
Cross post with Alistair, but he explained it very nicely
Because that significance only becomes apparent when you look across many, many individuals. If you have a thousand samples and you find a correlation that describes on average every extra inch of height results in 10 extra IQ points, it doesn't mean that every given individual at 5'4" will have an IQ of 110 and someone at 5'5" will have an IQ of 120.
The statistics do not care what the proximate cause of the link between IQ and height is, however this doesn't mean that these can be disregarded when analysing the data.
Consider for instance the effect of potentially genuine medical conditions which cause extreme short stature (say for example less than five feet), which may be coupled with cognitive deficiency. If a genetic disorder at the one extreme end of physiology was occuring, this would result in an apparent 'correlation' between height and intelligence, but it would mean nothing in real terms as it means nothing to people which vary in height closer to the mean.
Furthermore a 'correlation' may be significant i.e. the probability of it coming about by chance is slim, which means an observable effect is present, but the actual R value of said correlation could vary hugely. Two different correlations can be equally significant but there effects can be much smaller. Without knowing the actual level of 'effect' a significant correlation can be still be weak, which would mean that it would be useless for any one individual to be able to work out whether they are smarter or less intelligent than anyone else based on their height.
These factors could be very
indirectly linked, let's say for instance that height is linked to head
size, which is linked to brain size, which is linked to intelligence.
Then there is a correlation between height and intelligence, but it
still means that a tall person might have a relatively small head for
their size, resulting in lower than expected IQ.
For this reason it is important to remember that correlations done on a large scale study should not be used by an individual to work out their 'risk'. A gene may be associated with heart disease i.e. in a study of 1000 people those with a copy of this gene are twice as likely to develop heart disease as those without it. However as our knowledge of human biology is incomplete, it is not possible to say to a man with this gene that he is 'twice as likely to develop heart disease as the average man', for instance does this particular man exercise? Then his risk might be double what it would be if he didnt have the gene, but it is now less than double the average risk, let's say 150%. Now consider the fact that he may have other genes in his body, which are also involved in heart disease, but this time they are beneficial, now his risk of heart disease may actually be less than the national average. But we don't have a study which has shown the effect of those genes, so we know nothing about it.
Taking it back to height, we don't know the other, hidden, potentially stronger impacts on intelligence, both genetic and environmental that mean when we try to estimate an individuals IQ based on their height we are going to fail.
I don't believe so, in a complex case such as this with not only mutliple genes involved, pleiotropic effects, genotype by environment interactions to generate a phenotype, potential epigenetic effects as well, all spread across two traits, both not fully understood but with a mild correlation between the two. Then yes there is a probability, but it is so vanishingly small, and uncertain given that we don't yet understand all the factors involved that it is meaningless when trying to work out whether any given person will have a particular intelligence based on their height
Animal behaviour is a very widely studied area of Biology, I work on it, as do most of my colleagues in my department (70-100 people, professors, post-docs, phds and technicians).
Animal behaviour studies cross a wide range of subject matters, I study behaviour as part of wider studies on evolution and sexual selection, others might tackle them from a neurology point of view or a conservation perspective etc. So in university research it is plentiful and you will find people doing such work all across the country. Conservation organisations such as the RSPB are often carrying out such work in order to better understand how to conserve rare species etc.
So behavioural studies can be anywhere from entirely lab based, entirely field based and every point in between.
Money varies greatly and really depends on who you are working for and what qualifications you have and what stage of your career you are in. Try browsing the careers pages for more idea of what an academic might be paid, work in conservation is often more popular and as such less well paid, but people mostly do this work for the love not the money.
Unfortunately we won't be able to pin down exactly why you are short, height is a very variable trait based on genetics and environment. It is generally a fairly heritable characteristic, but one which involves the inheritance of multiple genes, some of which may be recessive. For instance, two short parents are unlikely to have a tall child and vice versa, however occasional exceptions to this rule do occur. I would hasten a guess that at least one and probably both of your parents were below or average height, although obviously this can't be verified.
Activities such as playing basketball will not influence your height, it is determined by genetics and nutrition, assuming you were fed a varied diet as a child and adolescent you should reach your full genetic height potential.
Now as for the link with intelligence, there is a significant link between height and intelligence, as in the average IQ of someone of the same sex at 6ft is greater than that of someone at 5ft. This could simply mean height is a marker for good health and nutrition while growing up, which will help increase intelligence, or there may be some genuine genetic link.
However I must stress at this point that these are correlations, therefore people can and do deviate from this trend greatly. And given the multifaceted nature of both height and intelligence, it means that while if you took 1000 tall people and 1000 short people and found a different average intelligence between the groups it would still mean that when comparing one short person to one tall person you could make absoultely no guesses as to who would be more intelligent. Trends mean nothing to the individual
Hey so some interesting questions here, which I will endeavour to try and answer.
Ok sorry if I pick apart some of these statements a little, but it is important as a scientist to only state what the facts demonstrate and not try to make too many suppositions. So statement one, 'when we are startled we hold our breath', im not sure about this one, i think people can display a range of reactions, screaming, holding their breath, gasping etc. also when if one is startled and holds their breath, it is much more likely that holding your breath is a byproduct of the body tensing up, the muscles go rigid in preparation for fight or flight. Therefore it is the muscles preparing themselves for action which gives us strength and holding your breath is an inadvertent side effect of this. Indeed when lifting weights in the gym one is advised to breath out when lifting, as we often naturally hold our breath but it is detrimental to our lifting ability (no oxygen is getting in!)
As a practitioner of the martial arts the 'kiai' is used for several reasons, the diaphragm rises and helps tense the abdominals, this primarily means that should you be hit while attempting to hit someone else you are less likely to be winded by the attack, it also has some psychological aspects, shocking the opponent etc.
But I'm afraid at this point you lose me, I do not follow the subsequent link to crying or what you think the causes are.
I would also caution against using logic or inferences to explain why something occurs. Just because it makes a good story, doesn't mean that it will be the ultimate reason why something occurs, biology is messy and the neatest answer is not necessarily the correct answer.
I hope I have answered some of your question, please post again if you want to try and discuss crying more (or anything else for that matter)
Well children have big heads, because a lot of the complicated wiring required for babies to learn and develop are in place before birth. If they weren't and the head was more in proportion to the body then development after birth would take even longer. It is generally accepted that the human baby head size is a compromise between the need for a relatively large brain capable of learning and the limitations on what can actually fit through a pelvis during childbirth.
The human brain does continue to grow during childhood and adolescence, reaching a peak sometime around puberty I believe, after which a lot of pruning occurs, essentially tweaking the wiring to optimise efficiency.
Though all of this is a gross oversimplification and human neural development is a vast and fascinating area of research, and while some types of neurons like grey matter may be increasing, white matter may be decreasing. Neurons may be dying off, but resulting in a greater intelligence as the brain 'streamlines' etc.
Men and women are basically the same, we have pretty much all the same parts, although they may differ in size and shape slightly. So both men and women have the same basic body plan, because we are after all the same species. In women there is a development of large breasts in order to breastfeed babies, but men still have breasts, they are just much smaller, they are not enlarged when boys hit puberty in the way that girls are. But the structure is the same, and that's basically my point, it is very difficult for something to evolve in only one sex and not the other, given that we all share the same genes and body plan, rather it is much easier for the basic plan to be present in both sexes and then enlarged or altered in small ways for it be used in women but not men.
If nipples were a problem for men, then it is possible we would have evolved not to have them, but they are neither useful or harmful, so we men have nipples because women NEED nipples.
Well that would be due to the fact that your joint bends in one direction, therefore there is an excess of skin on the knuckle as when the joint is bent the distance between the posterior of the knuckle to the anterior is greater on the back of the hand than the palm of the hand. So an excess of skin is required on the back of the hand for when the joint is flexed, but the palm side needs to be able to crease and fold, an excess of skin on this side would actually hinder joint flexing.
Hope that explanation helps!
Not exactly my field of expertise, but I believe the ridges along your fingers allow better detection of patterns on fine surfaces, as these ridges run along a surface the pressure (or lack of) on each surface allows fine scale detection of texture. Much more so i imagine than if your finger was entirely smooth.
And yes, your hands and feet are rarely exposed to continuous or sustained direct sunlight and as such are much lighter than most other parts of the body.
Great question, at the short answer is no, but it often undoubtedly helps! There are two broad 'types' of speciation, allopatric and sympatric. Allopatric speciation refers to the situation where two species separated by geography, over time evolve into two separate species. This may come about through different ecological pressures which drive the now distinct gene pools in different directions, until eventually they are so different as to be classified as separate species, ones where even if the geographical boundary were taken away they would be unable to produce fit and healthy offspring. There are some caveats to this rule, sometimes a hybrid might be possible, but generally they are of substantially reduced health or fertility, such that it is still unlikely that the two species could ever hybridise to form one species. In addition there doesnt need to be any real 'selection' for speciation to take place. Genetic drift is a process whereby mutations gradually spread through populations to fixation, as mutation and drift are both random, two originally identical populations will gradually become distinct over time as they accumulate different mutations.
The important thing allopatric speciation requires is simply isolation and time, eventually separate species will emerge. This is considered to be the most common method of speciation.
However there is also sympatric speciation, where speciation occurs without a prior geographical barrier being established. As you might imagine this is far less common, as the reproductive barrier must be established while the two populations are intermingling. Suggested methods include selection for homozygosity, whereby organisms which have two of the same kind of allele are fitter than ones which have one of each kind of allele, this establishes very quickly a fitness cost to 'hybridizing' the difference between these groups might only be one gene at first, but if the hybrids always fail then they are reproductively isoalted and drift or selection can take place as described above.
Well studied modern day examples are the apple maggot fly or the cichlid fish of the african lakes. Try googling them for more information and feel free to ask on here again for more information as well!