Gaining Insight into Evolution and Natural Selection

[Laroxe]

I wonder if there is an issue in seeing survival and fitness as being the same, they are related but the important thing in evolution is in passing on the genes in question, survival is only relevant in lasting long enough to achieve this, there are lots of examples of attempts to increase fitness reducing chances of survival. There are lots of things than can potentially induce mutations in the genes and many traits that exist along a continuum. Mutations are usually random chance events some being more common than others but there is then the issue of the animal being able to reproduce, another huge element of luck. To effect things at the population level usually involves the element providing an advantage in a given environment. There have probably been people with a natural resistance to HIV infection for centuries because of a common genetic variant but its only now that we could expect to see an increase in this variant in the population. A selective advantage may have nothing to do with survival it may just make the animal more attractive to the opposite sex.

 

[lavinia]

I clipped and sent the OP's opening post to a biologist friend and asked for any comments. I said that the post seemed skeptical about evolution Here is his response

"
... So, dealing with these issues one at a time...

1) Terrier digging. Assuming that terriers actually dig more than other dogs, then breeding for the trait involves selection on the basis of phenotype, NOT genotype. Whatever makes one dog dig more than the next is selected for positively, while the bad diggers are not allowed to breed. The genetic component of this behavior is not a single gene, but is a phenotype generated through the actions of multiple genes. The genes involved may encode structural proteins that somehow predispose to digging (bigger claws, let’s say), but may also produce regulatory proteins that affect the expression of multiple other genes. Final phenotype, aggressive digging, need not SURVIVE embryonic development. it might, in fact DEPEND on developmental processes in the embryo and fetus.
Subtle traits are thus the result of a complex orchestration of coding gene products, regulatory genes, interactions of cells during development, and events that may affect development after birth - that is, epigenetic factors. That these processes lead to highly complex and subtle traits may be mind boggling to the author here, but the development of a multicellular organism, and the myriad mechanisms that underlie this development, are very complex indeed. In this particular case, one could hypothetically envision selection for a claw structure that the dog finds irritating, with the irritation relieved by digging. That’s not so complex. I rather believe the trait is neurologically based, but my point is that from a genetic standpoint, seemingly complex traits might be simpler than they appear.

2) As for the post on dreaming, I’m not sure what the person is getting at. Obviously the brains of higher mammals are larger and more complex than those of fish, perhaps dinosaurs, or even shrews. That this greater size and complexity is associated with dreaming is simply an observation. Clearly there are some animals whose nervous systems would not seem compatible with dreaming - insects, for example. After all, insects and humans evolved from a common ancestor.

3) Cow tails. First of all, the cow is a domesticated species, and both its breeding and maintenance are not “natural” from the point of view of natural selection. If the ancestral feral cow had a tail or eyelashes that were less efficient at keeping away flies, and if fly bites hampered reproduction, then yes these traits are the product of natural selection. The author should consider the point that if one cow is bitten even a little more often than another because of its inferior tail or eyelashes, it might indeed breed less efficiently. Flies and other insects are vectors for disease, and a sick animal might well breed less successfully. The number crunching element of this post (what exactly is a gajillion, anyway?), seems to suggest that the author believes selective advantages are “all or nothing”. That is, the disadvantaged creature never has offspring, while the one with more fortunate genes always breed successfully. This is not usually the case. Over time, a small advantage in reproduction can go a long way towards evolution of better adapted phenotypes, even if the “inferior” members of the species continue to produce offspring, albeit with less success.

4) Pebbly skin and long legs. Here again, I’m not sure what the author is driving at. A factor in evolution that he/she seems to be underestimating is the importance of speciation. Once a critter has a significant advantage over others of its kind, it will breed much more efficiently with those members of the species that are more similar to itself. These process leads to reproductive separation, and ultimately, isolation from the predecessor. The consequence of this process is speciation, and each new species then “responds” to its selective environment in a new way. Note that the ancestral species might not even become extinct, though extinction is certainly a significant part of evolution. A scenario other than extinction night consist of the ancestral species being left in an ecological niche that favors short-legged, pebbly-skinned critters.

 

[houlahound]

thanks for seeking an insightful response.

in fact in working dogs I believe there has only been one attempt at a micro/gene level study of working traits and genes. the study was on working kelpies and was in part funded by the farm lobby.

one thing I can state is that working traits are not fixed in a line or breed, they can be made more stable by heavy line breeding (within families) but experience has shown that for something like herding instinct the trait can be greatly diminished as to be worthless within 3 generations hence in the real world often brutal testing and culling is performed on every litter. that is reality, that's how it has been done for centuries and precisely what created the various working breeds to begin with. of course these days a market has opened up for show and pet dogs so the culling has been replaced by selling which explains the world-wide diminishment of working traits in dogs.

 

[Bystander]

thanks for seeking an insightful response. ... the culling has been replaced by selling which explains the world-wide diminishment of working traits in dogs.

Ah-hah.

 

[houlahound]

nuff said;

http://www.documentarytube.com/videos/pedigree-dogs-exposed

 

[lavinia]

Continuing a little on the dreaming example. It seems that an evolved structure may have characteristics that were not directly selected for e.g. dreaming in mammalian brains. I asked my biologist friend and he wrote,

"That’s a good question. To answer that particular one we’d have to find the ancestral organism that first dreamed, and then try to figure out if dreaming provided some selective advantage. I think the general principle is correct, though, that structures with features that provide a selective advantage may have what’s called “emergent characteristics” which themselves were not the direct result of selective pressure. "

 

[Ygggdrasil]

Continuing a little on the dreaming example. It seems that an evolved structure may have characteristics that were not directly selected for e.g. dreaming in mammalian brains. I asked my biologist friend and he wrote,

"That’s a good question. To answer that particular one we’d have to find the ancestral organism that first dreamed, and then try to figure out if dreaming provided some selective advantage. I think the general principle is correct, though, that structures with features that provide a selective advantage may have what’s called “emergent characteristics” which themselves were not the direct result of selective pressure."

Stephen Gould and Richard Lewontin wrote a famous paper in the field of evolutionary biology about how traits can arise not as a direct result of adaptive selection, but as a byproduct of natural selection. They referred to such traits as spandrels.

 

[lavinia]

Stephen Gould and Richard Lewontin wrote a famous paper in the field of evolutionary biology about how traits can arise not as a direct result of adaptive selection, but as a byproduct of natural selection. They referred to such traits as spandrels.

Thanks for the link. I would love to read the paper.

 

[Ygggdrasil]

Thanks for the link. I would love to read the paper.

If you can't access the paper from the journal, a free version is available here: http://faculty.washington.edu/lynnhank/GouldLewontin.pdf

 

[houlahound]

Why are people insisting dreaming has to provide a survival advantage, it may just as well be a useless by-product of normal brain function.

 

[DaveC426913]

Thanks lavinia. Great answers. much food for thought.

houlahound. Agreed. I don;t think dreaming is a survival advantage, I think it's emergent too.

What I was trying to get at is that, for all creatures, no matter how separated in the tree of life, their common ancestor (that little shrew, running between the legs of T. rex) would have had that ability, passing its complex, dreaming brain on to all its descendants. Dreaming is ancient indeed.

 

[mfb]

What I was trying to get at is that, for all creatures, no matter how separated in the tree of life, their common ancestor (that little shrew, running between the legs of T. rex) would have had that ability, passing its complex, dreaming brain on to all its descendants. Dreaming is ancient indeed.

Not necessarily, things can evolve in separate branches of life separately. Eyes are a typical example, they evolved many times (estimates are 40-100) independently.

 

[DaveC426913]

Unlike its sister show, Star Trek, which tried to explain the tech and ended coming up with a lot of BS.

Not necessarily, things can evolve in separate branches of life separately. Eyes are a typical example, they evolved many times (estimates are 40-100) independently.

Yes. Convergent evolution.
Though I suspect in this case, it's really common ancestral trait.

 

[Pythagorean]

Yes. Convergent evolution.
Though I suspect in this case, it's really common ancestral trait.

I always wonder about this. For instance, the bill of birds and the platypus can be said to be a case of convergent evolution. But we're really only talking about macroscopic morphology aren't we? Do alpha and beta keratin ultimately come from the same ancestor and thus share the micro-structural morphology that allowed both animals to grow a bill?

 

[BillTre]

Just found this discussion.

Here are some other things to consider:

1)
There is a lot of genetic information in modern animals (including humans):

• 10⁸ to 10¹¹ base pairs (each a choice of 4 possibilities)
• 10-40,000 protein coding genes
• unknown numbers of other non-protein encoding genetic elements

There's lots of inherited information there. This information is available to each cell in each animal (billions in people) to possibly be used independently.

2)
Many (most?) traits are what I would call generative. They are not encoded directly in the genome. They are assembled during collaborative events during development, usually involving many cells using many sources of genetic information. Each of these cells and genetic factors will have some capabilities and dependencies that are different from other kinds of cells or genetic factors. This kind of stuff is somewhat hidden and not easily observed since it is microscopic and chemical in nature, and is often hidden inside developing eggs or a pregnant mother.

The nervous system and the behavior it generates is like this. Single genes can have an effect but they are embedded within the developing system in which they find themselves (the individual animal). The population’s shared genetic resources will affect the success of a novel gene in such a situation. If a gene is successful in one animal out of a population of a million, but the other animals in the population lack the supporting cast it will not workout well for the gene in the long run, until it can frequently encounter the right supporting cast as it makes its way through the succeeding generations into which it gets bred.

3)
Evolution usually deals with large numbers of individuals combined with many repetitions over time (a multiplicative increase in the number of adaptation tests). Weak traits (small adaptive advantage) can be strongly selected (to achieve high frequency in the population) in larger populations over many generations of time. The many repetitions of the selection process (each short generation) can continuously ratchet up a gene’s frequency as it gradually becomes more widespread in a population.

Cow tail/eyelashes could have a small effect on breeding success in a single generation but over many generations (involving small statistical differences in survival/breeding) can lead to a situation where all animals in a species have a particular trait.

Scenario: Perhaps the longer hairs reduce the likelihood of flies infecting the cows with as many parasites as its shorter haired relatives (or draining them of so much blood), which makes them better able to provide for their offspring, who are then more likely to go on and breed.

I think there are examples similar to this in biological aspects of aquacultural engineering where calories in/health vs. growth/reproductive state are studied quantitatively.

Perhaps the individual vs. the population could be thought of as something like wave and particles.
But wait, there’s more: Another way to think about these things is to consider genes and the selection on them as they get their genetic ride through generations of organisms. This is the idea behind the Richard Dawkins’s 1976 Selfish Gene book (https://en.wikipedia.org/wiki/The_Selfish_Gene).

4)
Dogs:
Hunting dog behavior has been lead people to following view:
Wolves (from which dogs are derived) had well developed hunting skills selected for over probably millions of years. People can along and domesticated dogs evolved. As people started to select dogs for traits that the people found useful, the ancestral wolf traits were modified. The genetic modifications most likely to be randomly generated are those that break things (most mutants people collect in mutant screens are the equivalent of throwing a monkey wrench into the biological mechanism). Different strains of hunting dogs are thought to use the wolf’s basic hunting sequence of actions (which might be: find something, chase it, kill it, and eat it) but different different genetic lines of dogs can have breaks inserted into this behavioral sequence at different places, resulting in different behaviors.

Generally, new traits are considered less likely to randomly evolve. However, given enough time and chances and an environment (as well as a supporting cast of other factors) where it would be adaptive, these kinds of things can pop up.

A recent example of such a mutation might be the cause of the evolution of a smoother gait in horse which arose about 1200 years ago in England and/or Iceland (https://www.sciencemag.org/news/201...asier-ride-horses-evolved-more-1000-years-ago).

I don’t know about the dog digging, but it seems to be something that all dogs do (in my experience). I would therefore think it is a primitive feature, not evolved anew in terriers.It maybe magnified however.

 

[ebos]

This is probably the most important thing on this thread that I hadn't seen discussed in detail. It's called sexual selection and it affects the course of evolution in sometimes unpredictable ways (e.g., peacock's tail). So maybe cows find long eyelashes attractive? Humans seem to, even though it provides no discernible survival advantage to us.

It probably does in the long run. However, it appears that at this moment in time, our sexual selection is questionable.