Natural Selection, why not even better?

[Torbjorn_L]

At some point in our history, we developed, for lack of a better word, humanity. The desire to not kill or let our fellow humans die, no matter their characteristics, or weak or strong mutations.

Such a humanity evolved very early. The earliest example may be eusocial ants, whose lineages split over 100 million years ago. [ http://en.wikipedia.org/wiki/Ant ]

"Eusociality is the highest level of social organization. It is characterised by:

Overlap of adult generations
Reproductive division of labour
Cooperative care of young"

[ http://en.wikipedia.org/wiki/Social_animal ]

Whether eusocial organisms weed out differences in youngs are specfics - we do it as well - they certainly may euthanize sick individuals - we do it as well (Belgium IIRC, sufferers may ask and get it).

This was a prelude to a "societal norm," where people who were different, good or bad, were ostracized and unable to pass on that trait, which has led to a general stagnation of our species, where the only things really changing are height and skin color.

The link above goes into evolution of sociality, which is an old phenomena indeed.

As for humans, as you could surmise from my earlier comments, evolution works better than ever. Since we are so numerous (efficient evolution) and since it happened recently (change in environment), we should be among the fastest evolving animals these days. And, arguably, that is what science has found:

"Still, a very small fraction of the mutations in any given population will be advantageous. And the longer a population has existed, the more likely it will be close to its adaptive optimum -- the point at which positively selected mutations don't happen because there is no possible improvement. This is the most likely explanation for why very large species in nature don't always evolve rapidly.

Instead, it is when a new environment is imposed that natural populations respond. And when the environment changes, larger populations have an intrinsic advantage, as Fisher showed, because they have a faster potential response by new mutations.

From that standpoint, the ecological changes documented in human history and the archaeological record create an exceptional situation. Humans faced new selective pressures during the last 40,000 years, related to disease, agricultural diets, sedentism, city life, greater lifespan, and many other ecological changes. This created a need for selection.

Larger population sizes allowed the rapid response to selection -- more new adaptive mutations. Together, the the two patterns of historical change have placed humans far from an equilibrium. In that case, we expect that the pace of genetic change due to positive selection should recently have been radically higher than at other times in human evolution. ...

So to test the null hypothesis, we should look for evidence of these fixed selected substitutions. ...

This large number of completed sweeps should have vastly reduced human genetic variation, because polymorphisms tend to hitchhike along with nearby selected alleles. Hitchhiking up to fixation tends to eliminate variation. When we look at the effect of hitchhiking under this constant selection hypothesis, the genome-wide average diversity should be less than a tenth of what we actually observe. So that also disproves the null hypothesis. ...

Our evolution has recently accelerated by around 100-fold. And that's exactly what we would expect from the enormous growth of our population."

[ http://johnhawks.net/weblog/topics/evolution/selection/acceleration/accel_story_2007.html ; my bold]

That our species has "stagnated" is a poor guess, and it seems contradicted by observation.

 

[Torbjorn_L]

Wheels are defined as a circular component that rotates around an axial bearing. Rolling or cartwheeling organisms are not wheels.

Ah, thanks! We have a language difficulty, english isn't my first language, and that was a nuance lost on me.

On the other hand, there is an animal that has evolved an axial bearing, but it is a screw:

"Here’s the only figure in the article. It shows reconstructions of the ‘coxa’ (the first leg joint, where the leg joins the thorax) in green, and the trochanter, the first leg segment, in yellow. The coxa is the thread, the trochanter the screw. There’s also a nice scanning electron microscope image of the trochanter. The system works pretty much like your hip does – except the knobbly bit at the end of your hip has turned into a screw shape. (All the nerves and stuff run down the centre of the trochanter.) Most insect joints work like hinges."

So why doesn’t the leg unscrew itself? Most of the weevil’s leg motion will not involve a 360 degree rotation, or the hapless insect would get stuck after a couple of paces. Instead it will simply swing back and forth. Doesn’t the leg get blocked when it’s screwed into the max? Presumably so, in which case careful observation should show weevils back-pedalling to unwind their legs. And conversely – why doesn’t the leg come unscrewed? The muscles appear to hold it in place. Phew!"

"Now why does the weevil have this odd arrangement? The obvious advantage is that you can rotate the leg right round. But in that case, why not evolve the axle/wheel combination? The authors speculate that the screw might be better:

We suggest that an advantage of this construction is that the leg comes to a stable resting position, preventing passive straining of leg muscles, which would not be accomplished by an axle construction.

Above all, they think that it might be the weevil’s unique feeding posture, where it shoves its rostrum (its ‘snout’) into its food, that holds the key. Substantial forces will be generated on the weevil’s legs as it tries to grip the substrate; having a screw would effectively block the rotating joint, stopping the weevil from ending up with its head smashed in the food."

[ http://whyevolutionistrue.wordpress.com/2011/06/30/the-weevil-with-screws-in-its-legs/ ]

So it is has a partial wheel action, if I understand the objection correctly, and it could have evolved a another type of axis if the evolutionary constraints had been slightly different.

[On another note, it is odd if this 2011 paper hasn't gotten more around more re this topic.]

The general reason why wheels aren't evolved is likely that they are impractical and inefficient for most animal or plant uses (uneven "road", as seen here tiring for muscles).

Gears, screws, ... what will they come up with next? Windows and lenses!?

Slit lamp image of the cornea, iris and lens (showing mild cataract) [ http://en.wikipedia.org/wiki/Cornea ]

 

[Drakkith]

Ah, thanks! We have a language difficulty, english isn't my first language, and that was a nuance lost on me.

No problem!

 

[Rocky9242]

>>Apart from a big brain, we have lost most anything else that is considered 'advancement', we are weak, slow, don't see or smell well, we can't run fast or that far.

Apparently, we can run "that far." See this Wikipedia article on "persistence hunting:"
http://en.wikipedia.org/wiki/Persistence_hunting

 

[Rocky9242]

Why haven't any animals evolved wheels? Surely that would be an improvement for speed.

A lot of animals have evolved rotary bearings. It would not be much of a stretch from there to place a wheel on the end of that axel.

Some animals make themselves into "wheels" (or balls or something) that can roll downhill.

This Wikipedia article has a good discussion of these structures and issues related to their evolution:
http://en.wikipedia.org/wiki/Rotating_locomotion_in_living_systems

 

[Drakkith]

A lot of animals have evolved rotary bearings. It would not be much of a stretch from there to place a wheel on the end of that axel.

You don't appear to have read this thread or the wiki article you linked very well. A wheel and axle are nearly impossible to develop by evolution.

 

[Torbjorn_L]

A lot of animals have evolved rotary bearings.

By your own reference, we know of no macroscale examples.

You don't appear to have read this thread or the wiki article you linked very well. A wheel and axle are nearly impossible to develop by evolution.

As of 2011, the weevil is in the details. See my previous comment https://www.physicsforums.com/threa...hy-not-even-better.765834/page-2#post-4872429. It seems eminently possible in arthropods, just not likely.

The conclusion I drew there was that wheels aren't evolved likely because they are impractical and inefficient for most uses (uneven "road"; as seen in the weevil example tiring for muscles). But I know of no way to test that beyond the weevil find.

 

[Ygggdrasil]

Why haven't any animals evolved wheels? Surely that would be an improvement for speed.

Would wheels really be an improvement in speed? Sure, if you're on something perfectly flat and straight like a road, wheels are advantageous, but life did not evolve in an environment with roads. For moving on uneven terrain, wheels seem less advantageous than legs.