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Evolution

Below are some thoughts about evolution, covering:
  1. Was the extinction of the dinosaurs caused by an increase in gravity?
  2. Why can insects jump so high, relative to their body size?
  3. Why did humans migrate out of Africa during the ice age? (with possible implications for climate-change modelling)
I also hypothesise about the evolutionary benefits of being gay (& some things that make women attractive to men) here.

1. Were dinosaurs killed by an increase in gravity?
Gravity & electromagnetism are linked and the earth's magnetic field 'randomly' changes from time to time, smaybe a sudden dramatic change in the earth's magnetic field caused the earth's gravity to increase perhaps when hit by a meteor that almost penetrated the earth's crustwhich could well have disturbed the flow of ions in the earth's core that affect its magnetic field (It's hardly surprising we can't measure the gravitational constant accurately if it keeps changing!).  And maybe that's what killed the giant dinosaurs - they were too big to move around under the higher gravity, and giant pterosaurs like Quetzalcoatlus (with a wingspan of up to 16m!) became too heavy to fly (and modern birds haven't evolved to the same size, given weight increases with the cube but wing area only increases with the square of body dimensions).  This explains why they died whilst small dinosaurs survived as birds, even though being large should have been an advantage for maintaining body temperature when the planet suddenly cooled (since large animals lose less body heat because they have a lower surface area to body mass ratio, which is also why megafauna like the mammoth got too hot and died out after the ice age, whereas whales survived as they have the sea to keep them cool).  Conversely, the massive volcanic eruptions at the end of the triassic may have thrown enough dust into space (forming earth's dust moons) to reduce gravity and enable the growth of the giant dinosaurs in the subsequent jurassic period.
However, some crocodiles survived the final end of the dinosaurs, for reasons that scientists can't understand (given other dinosaurs didn't), and so did turtles (who also date back to the early dinosaurs) - both of whom live in shallow waters, which could partially support their weight when gravity increased and enable them to crawl up for air (whereas giant prehistoric sea creatures like plesiosaurs would have sunk and died on the sea bottom if gravity increased).  They even look like their bodies suddenly got too heavy for them - forcing them to inefficiently drag it along the ground with their legs splayed out the side (whilst strangely, other variants with the more efficient leg structure that is common to other animals - perpendicular to the ground - died out).  This might also explain why crocodiles developed an unusual ability to pull organs out the way of expanding lungs, in order to increase buoyancy - a muscle strength they could conceivably develop within months, or certainly faster than evolving other changes (like a larger chest cavity or an air bladder like fish) in response to a sudden increase in gravity.
So the higher gravity we have now may be why the only new giants to evolve since the dinosaurs are whales, with their weight supported by the sea.
And if the earth's magnetic field suddenly flips again, maybe gravity will reduce and we will all be able to jump over houses?




Alternatively, it may be that the meteor caused global earthquakes which caused giant dinosaurs like T-Rex to fall over and break their bones.
Talking of which...


2. Why can insects jump so high? (relative to their body size)
I was thinking it must be due to how fast they can transmit electrical signals to activate their muscle cells, and was it just the shorter distance or, by my theory of gravity, does a lower gravity force in a less massive object increase the speed of transmission? (and did this explain Stegosaurus' supposed, but now dismissed, extra brain near it's hind legs - as enabling it to move faster or better coordinated than it otherwise could?)
But my further research suggests the latter is unlikely, because neuro signals are actually quite slow - being limited by chemical processes, not the speed of light (although that said, it may have an effect as everything should go faster in lower gravity, which could explain why insects perceive & can react to events faster than humans, and also age faster, which essentially means time seems to go slower for them as they pack more experiences into their short lives).
However, it seems jumping ability is ultimately because of atomic structure and gravity, as I explain following:
  • The strength of bones and muscles in tension is determined by atomic-scale electron bonding, which means the total force they can withstand increases with their cross-sectional area, or the square of body size measured along one dimension (e.g. length).
  • But body mass and total force required to achieve a certain acceleration (up to 'launch speed', to jump a certain height) increases with the cube of body length.  So if an animal was simply scaled up in size, for example with its length & all other dimensions increased by a factor of four, then the maximum force that its muscles can withstand without breaking would increase by a factor of 16 (4 squared), but its mass would increase 64-fold (4 cubed) so the larger animal could only accelerate its limbs at one quarter of the rate of the smaller animal (16/64, from Newton's 2nd law, F=m.a).
  • Now with longer limbs, the acceleration could continue over 4 times the distance before the animal leaves the ground, but with one quarter of the limb acceleration, the launch speed will be the same as the smaller animal (by v^2 = u^2 + 2.a.s where u = 0),  Then with the same gravity force slowing it as it rises in the air, the maximum jumping height should also be the same, not proportional to the body length.
  • However, when they fall down, all masses fall to earth at the same rate of acceleration (9.8m/s/s) and thus hit the ground at the same speed when falling from a given height (ignoring air resistance, which will slow smaller animals like cats to a greater extent).  Hence the force impact of landing may increase with close to the cube of body length (proportional to mass), unless the animal can master a very controlled landing that allows the deceleration of ground impact to be slowed over the extra body length (like a 'parachute roll' landing).  Hence, as the cross-sectional area that must withstand this force only increases with the square of body length, a larger animal will likely suffer almost proportionately bigger stresses and injuries on landing, especially with an uncontrolled fall.  This must be why Walking with Dinosaurs (episode 6) says a T-Rex will kill itself if it simply falls over (& an elephant could have crippling injuries), although as this seems a rather fatal evolutionary design flaw, perhaps gravity was lower then than it is now (see above)!
  • Some insects have evolved ways of jumping higher, such as hydraulic/catapult-like muscles and distributed nodal nerve systems that reduce the travel-time for muscle-switching signals, but I suggest they've only evolved these mechanisms because unlike larger animals, they can exploit them without killing themselves when they land!
  • And so we see that the size of animals on earth is fundamentally determined by the size of atoms (which dictates the strength of muscle & bones) and the size of the earth (which determines the magnitude of gravity and acceleration of all objects when falling to earth)!  If the earth was bigger, gravity would be too great for larger animals to jump or fall and survive.  And if the earth was much smaller and had less gravity, then essential life gasses like oxygen molecules would exceed the earth's escape velocity at room temperature and escape off into space.
Not only is this fascinating in itself, in explaining how diverse life on earth depends on the size of atoms and our planet being just right (amongst many other enabling factors), it reinforces just how unlikely it is that complex life will form on any other planet, as I discuss in relation to the supposed Fermi Paradox.


3. Why did humans migrate out of Africa during the ice age?
Finally, I'm not sure if this has anything new, but here's some tentative conclusions I reached whilst wondering why modern humans (Homo-sapiens) migrated north out of Africa about 100,000 years ago, just when a major ice age glacial period started (& related to that, why are black people's palms & feet-soles white?).

I think there must have been something bad happening in Africa then to force them north, because, as in marriage, people generally don't change unless they have to, & especially if you're going to have to move out to somewhere that seems a lot worse.  But if there were glaciers expanding south, surely this suggests that an otherwise hot Africa was also cooling, and becoming more habitable?  
So why did they head north to try and live in an inhospitable icy land?

The hypothesis I've come up with is that the expanded polar ice reflected & scattered light up to clouds & the earth's atmospheric edge where it was further scattered & reflected back down towards equatorial areas like Africa (more through scattering & bending than abrupt reflection, as the refractive index of the air gradually reduces at high altitudes due to lower air density & gravity).  So even if the increased reflection into space from expanded polar ice cooled the planet overall (compared to absorbing this light in land previously not coated by ice), and winds at least partially spread this reduced temperature across the globe, areas like Africa, though perhaps no warmer on average (or even cooler), would experience more intense solar radiation, which would burn pale human skin and increase deaths from skin cancer.  But if their skin was already dark, would it matter?  Perhaps it wasn't dark enough.

Also, is this scattered light reflection adequately captured in modern climate-change models?  If not, they may overstate global warming forecasts.  (The reflection of scattered light back towards the equator should moderate the accelerated cooling caused by increased reflection from ice into space as the ice caps expand, or conversely, it may moderate accelerated warming as ice caps retreat.)

Anyway, to inform/support my hypothesis, here's what I found from some research on human evolution & climate change:
The above indicates both early & modern human migrations out of Africa started soon after extensive glaciation events, some 800,000 and 100,000 years ago.
Is this coincidence?  It's the opposite of what you'd expect - if the planet was cooling and glaciers were expanding south, why on earth would you move north to try and live in a much colder, icy land?

It seems there must be rather counter-intuitive causation involved - the expansion of glaciers somehow forced some early and modern humans to migrate out of Africa.  And the only thing I can think of is that the increased level of light reflected from larger ice sheets in the north, reflected back again from the atmosphere down to Africa, causing more intense UV radiation.  Then, whilst some humans in Africa may have been able to shelter from the worst of the sun, perhaps in coastal caves, and/or evolve extremely black skin (with the reduced Vitamin D production offset by eating a lot of fish - consistent with the theory of "aquatic apes/humans", who would then also benefit from brain development and increased body fat in place of hairy skin), many humans inland either migrated to the icy north, or died of skin cancer.


* Note there also seem to be logical flaws in the Wikipedia explanations for the evolution of skin colour following loss of body hair, which relates this loss to bipedalism.
It explains that big quadrupedal savannah animals don't need body hair to stay warm if their body volume (relative to surface area) is large enough to retain sufficient heat, but this critical size is larger than a human, who one would therefore expect to retain their body hair in order to stay warm.  It then points out that an upright person has less body area exposed to the sun compared to a similar sized quadrupedal animal, and therefore should get less hot in the sun, but this logic seems to indicate an even greater need for body hair.  In any case, bipedalism developed 4 million years ago (or earlier), some 2.5 million years before the mega-drought that forced early humans out from the shade of trees into the open savannah, where they had to lose most of their body hair.


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