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Author Topic:   Interweaving Evolution & Hybrid Vigor
RAZD
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Message 1 of 8 (770161)
09-30-2015 1:14 PM


Heterosis defined
I was rereading the Peter & Rosemary Grant, Darwin's Finches and Evolution thread and in particular noted this passage from the initial quote (Message 1):

quote:
(The People Who Saw Evolution)

... It looked a lot like a fortis, but also like a scandens. Genetic analysis showed 5110 to be a cross between a fortis and a fortis-scandens hybrid. They called it “the Big Bird.”

The Big Bird had a unique song and, when mature, shiny black plumage that was different from the indigenous Daphne birds. It also was extremely “fit” in the Darwinian sense — and promiscuous, surviving another 13 years and mating with six females, producing 18 offspring. It mated with several fortis-fortis-scandens hybrids, then with fortis females, and began a new line of Big Birds that sang the song of the original immigrant.


And I also recall the discussion on New Species of Homo Discovered: Homo nalediHomo[/i] Discovered: Homo naledi of a "braided" history ... from the article:

quote:
This Face Changes the Human Story. But How?

Berger himself thinks the right metaphor for human evolution, instead of a tree branching from a single root, is a braided stream: a river that divides into channels, only to merge again downstream. Similarly, the various hominin types that inhabited the landscapes of Africa must at some point have diverged from a common ancestor. But then farther down the river of time they may have coalesced again, so that we, at the river’s mouth, carry in us today a bit of East Africa, a bit of South Africa, and a whole lot of history we have no notion of whatsoever. ...


Because Homo naledi is a mosaic of features some modern derived features and some preserved ancestral features, and that applies to other species, such that there is some mixing and matching going on, this suggests some hybridization in the past. We also know from DNA analysis that there was some hybridization with Homo neanderthalus (alt Homo sapiens neanderthalus )

Wikipedia defines Heterosis as:

quote:
Heterosis, hybrid vigor, or outbreeding enhancement, is the improved or increased function of any biological quality in a hybrid offspring. The adjective derived from heterosis is heterotic.

An offspring exhibits heterosis if its traits are enhanced as a result of mixing the genetic contributions of its parents. These effects can be due to Mendelian or non-Mendelian inheritance.

Heterosis is often discussed as the opposite of inbreeding depression although differences in these two concepts can be seen in evolutionary considerations such as the role of genetic variation or the effects of genetic drift in small populations on these concepts. Inbreeding depression occurs when related parents have children with traits that negatively influence their fitness largely due to homozygosity. In such instances, outcrossing should result in heterosis.

Not all outcrosses result in heterosis. For example, when a hybrid inherits traits from its parents that are not fully compatible, fitness can be reduced. This is a form of outbreeding depression.


An example of outbreeding depression would be horses, donkeys and mules, where reproductive isolation is not complete but usually results in sterility.

So outbreeding can result in hybrids that are more fit, equally fit or less fit, at which point natural selection would favor the more fit (heterotic) varieties becoming dominant in the population/s, leading to a new species group.

Crossbreeding is done a lot in animal husbandry and agriculture to develop improved stock, so it should not come as a surprise that it can occur naturally when daughter populations regain contact after undergoing different evolutionary experiences, but before they have evolved reproductive isolation.

The amount of independent evolution could vary a lot, as it is the development of reproductive isolation that would stop such interbreeding. Certainly when we see that hybrids can be made between lions and tiger or between lamas and camels after long periods of separation.

We also see this between European invaders and Native peoples of the Americas.

So the tree became a bush becomes an interlinked\braided bush.

         A
|
|
/ \
/ \
| |
/ \ / \
| \ / |
| | |
| | |
B C D

Where C is not the same as A, but is a braided mosaic of B and D. Note that A, B, C and D still form a clade descended from A.

This does not mean that evolution does not happen, just that the process is not a cut-and-dried cookie-cutter proposition. This also means that the definition of "species" is a little muddier than before ... and it was muddied before.

Enjoy

Edited by RAZD, : subt


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Replies to this message:
 Message 2 by RAZD, posted 09-30-2015 2:52 PM RAZD has responded

RAZD
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Posts: 19476
From: the other end of the sidewalk
Joined: 03-14-2004
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(1)
Message 2 of 8 (770169)
09-30-2015 2:52 PM
Reply to: Message 1 by RAZD
09-30-2015 1:14 PM


... and dogs (and cows and pigs ... )
Another application of this to the debate is when we look at animal husbandry, agriculture and breeding programs.

So outbreeding can result in hybrids that are more fit, equally fit or less fit, at which point natural selection would favor the more fit (heterotic) varieties becoming dominant in the population/s, leading to a new species group.

Now we can see in dog breeding that some dogs are bred to create an extremely inbred population in order to maintain the "breed" and that these types of breeds often exhibit inbreeding depression. These are the "show" dogs, but they are not the only breeds.

Another class of dog breeds are "working" dogs, where the appearance of the dog is not as important as the function. The sheep herding dogs come to mind. To my view they seem to exhibit Heterosis and not exhibit any of the inbreeding symptoms.

We can also look at cow and pig breeding, where the purpose is not some aesthetically "pretty" animal but one that fills a function (more milk, more meat).

From the Wikipedia definition of Heterosis again:

quote:
In proposing the term heterosis to replace the older term heterozygosis, G.H. Shull aimed to avoid limiting the term to the effects that can be explained by heterozygosity in Mendelian inheritance.[1]

The physiological vigor of an organism as manifested in its rapidity of growth, its height and general robustness, is positively correlated with the degree of dissimilarity in the gametes by whose union the organism was formed … The more numerous the differences between the uniting gametes — at least within certain limits — the greater on the whole is the amount of stimulation … These differences need not be Mendelian in their inheritance … To avoid the implication that all the genotypic differences which stimulate cell-division, growth and other physiological activities of an organism are Mendelian in their inheritance and also to gain brevity of expression I suggest … that the word 'heterosis' be adopted.

When the aspects of rapid growth, size and robust health are considered it is easy to see why this is pursued in husbandry.

Again, we can see how (properly applied) artificial husbandry practices offer a window into how natural evolution (mutation and selection) can operate.

Enjoy


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This message is a reply to:
 Message 1 by RAZD, posted 09-30-2015 1:14 PM RAZD has responded

Replies to this message:
 Message 3 by RAZD, posted 10-20-2015 12:03 PM RAZD has acknowledged this reply

RAZD
Member
Posts: 19476
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 2.1


Message 3 of 8 (771117)
10-20-2015 12:03 PM
Reply to: Message 2 by RAZD
09-30-2015 2:52 PM


Revisiting Punctuated Equilibrium ...
https://en.wikipedia.org/wiki/Punctuated_equilibrium

quote:
Punctuated equilibrium (also called punctuated equilibria) is a theory in evolutionary biology which proposes that once species appear in the fossil record they will become stable, showing little net evolutionary change for most of their geological history. This state is called stasis. When significant evolutionary change occurs, the theory proposes that it is generally restricted to rare and geologically rapid events of branching speciation called cladogenesis. Cladogenesis is the process by which a species splits into two distinct species, rather than one species gradually transforming into another.[1] Punctuated equilibrium is commonly contrasted against phyletic gradualism, the belief that evolution generally occurs uniformly and by the steady and gradual transformation of whole lineages (called anagenesis). In this view, evolution is seen as generally smooth and continuous.

In 1972, paleontologists Niles Eldredge and Stephen Jay Gould published a landmark paper developing their theory and called it punctuated equilibria.[2] Their paper built upon Ernst Mayr's model of geographic speciation,[3] I. Michael Lerner's theories of developmental and genetic homeostasis,[4] as well as their own empirical research.[5][6] Eldredge and Gould proposed that the degree of gradualism commonly attributed to Charles Darwin is virtually nonexistent in the fossil record, and that stasis dominates the history of most fossil species.

... Punctuated equilibrium differs from Mayr's theory mainly in that Eldredge and Gould placed considerably greater emphasis on stasis, whereas Mayr was generally concerned with explaining the morphological discontinuity (or "sudden jumps")[10] found in the fossil record.[7] Mayr later complimented Eldredge and Gould's paper, stating that evolutionary stasis had been "unexpected by most evolutionary biologists" and that punctuated equilibrium "had a major impact on paleontology and evolutionary biology". ...


The standard view iirc, is that a small subpopulation evolves in isolation, and then returns to the habitat of the parent population and displaces it with their better adapted phenotypes.

With the emerging thoughts on "braided" beginnings to new species and hybrid interactions during the early stages of new species formation, it seems more logical to me that the returning subpopulation interbreeds with the parent population and the hybrid offspring inherit traits from both populations, which are then selected for fitness, leaving a new population with hybrid vigor and a mosaic of traits.

This has the benefit of mixing the best of both populations within a larger breeding population.

Enjoy


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Admin
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Message 4 of 8 (771127)
10-21-2015 8:40 AM


Moderator Question
Is this a topic you wanted to discuss, or information you'd like placed over at Links and Information. If this is a discussion topic, how does it tie in with creation/evolution?

Also, I think punctuated equilibria when a population experiences a period of rapid evolution, as opposed to relative stasis. The population could subsequently return to displace the original parent population, but I think that's just competition, not punctuated equilibrium.


--Percy
EvC Forum Director

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RAZD
Member
Posts: 19476
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 2.1


Message 5 of 8 (771131)
10-21-2015 9:40 AM
Reply to: Message 4 by Admin
10-21-2015 8:40 AM


Re: Moderator Question -- the basic question for debate
Discussion, on how evolution works in regards to speciation. It's not always straight line process of speciation, but a little tangled, a little messy.

Also, I think punctuated equilibria when a population experiences a period of rapid evolution, as opposed to relative stasis. The population could subsequently return to displace the original parent population, but I think that's just competition, not punctuated equilibrium.

The basic idea behind punctuated equilibria, as I understand it, is that a smaller relatively isolated population undergoes rapid evolution, possibly to adapt it to a slightly different ecology. Then it returns to the parent ecology which has been in stasis (continually readapting to a static ecology) and has an advantage for survival or breeding, and then it takes over and displaces the parent population.

The question I am raising on this is whether full speciation of this daughter population is necessary, or would not a new varietal phenotype that can interbreed and form hybrids that join the best features in a mosaic of phenotypic traits be a valid or better explanation.

We have evidence of such mosaic evolution, the braided stream pattern noted on the Homo naledi thread for instance, and the Darwin Finch hybrid "big Bird" as another.

Enjoy


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This message is a reply to:
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Admin
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Message 6 of 8 (771152)
10-21-2015 1:09 PM
Reply to: Message 5 by RAZD
10-21-2015 9:40 AM


Re: Moderator Question -- the basic question for debate
RAZD writes:

The basic idea behind punctuated equilibria, as I understand it, is that a smaller relatively isolated population undergoes rapid evolution, possibly to adapt it to a slightly different ecology.

Right.

Then it returns to the parent ecology...

Possibly. Or it might migrate somewhere else. Or nowhere else. Or it might return to the parent ecology and co-exist with the parent. Or it might return to the parent ecology and find that there is no longer any parent population to compete against because it's gone extinct.

I thought what was novel about the punctuated equilibria idea was that the episodic nature of the fossil record wasn't necessarily just an artifact of an incomplete fossil record, that it could also be real.


--Percy
EvC Forum Director

This message is a reply to:
 Message 5 by RAZD, posted 10-21-2015 9:40 AM RAZD has responded

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RAZD
Member
Posts: 19476
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 2.1


Message 7 of 8 (771159)
10-21-2015 2:33 PM
Reply to: Message 6 by Admin
10-21-2015 1:09 PM


Re: Moderator Question -- the basic question for debate
Possibly. Or it might migrate somewhere else. Or nowhere else. Or it might return to the parent ecology and co-exist with the parent. Or it might return to the parent ecology and find that there is no longer any parent population to compete against because it's gone extinct.

True.

Part of the reason I want to open this to debate with others, particularly those that know more about this than I do.

I thought what was novel about the punctuated equilibria idea was that the episodic nature of the fossil record wasn't necessarily just an artifact of an incomplete fossil record, that it could also be real.

Indeed, but for my argument ("the part I want to focus on" ... ), especially in those areas where successive fossil layers show noticeably different forms.

Now, I would like to credit Faith for leading me to think in this direction while formulating responses to her argument and her questions on this phenomenon in the fossil record.

And I have another example that I am working on, which I will save till after promotion and some confirmation from others that I am not just blowing smoke.

Enjoy


we are limited in our ability to understand
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 Message 6 by Admin, posted 10-21-2015 1:09 PM Admin has acknowledged this reply

Admin
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Message 8 of 8 (771186)
10-21-2015 8:46 PM


Thread Copied to Biological Evolution Forum
Thread copied to the Interweaving Evolution & Hybrid Vigor thread in the Biological Evolution forum, this copy of the thread has been closed.
  
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