Thread: Soft/Hard Inheritance?

In the science of evolution there are the disputed terms of 'Soft' and 'Hard' inheritance. Hard inheritance posits that "the offspring inherit only [their parents'] connate peculiarities and not any of the acquired qualities" (Lawrence). Soft inheritance posits the opposite, and that we can pass on acquired characteristics. While the term 'Hard inheritance' seems to have more credibility and currency in evolution science, isn't this but a debate of semantics? Isn't Evolution itself "Soft inheritance". You could even replace the terms. How is then without soft inheritance humans have adapted to their peculiar environments in Sub-Saharan Africa (dark skin for UV protection) and elsewhere? Please help me with this. Thank you.

and let me clarify,

The term 'Soft Inheritance' could be replaced with "Adaptation", am I not wrong? Adaptation is the integral function of Evolution. Which is facilitated by natural selection.

I don't think it's just a semantic issue. Firstly, when talking about the genetic aspect of traits, there is no passing on of acquired "traits," so to speak. If as an adult you develop a mutation in some of your body cells, that mutation is not going to be passed on to your offspring. If as an adult you have a mutation in one of your sperm/egg cells, then that mutation could go to your offspring, but that mutation won't affect you as an individual, so it couldn't be considered a "trait" that you yourself acquired.

Things possibly get a little fuzzier when you're talking about more environmental effects. If you raise your offspring in the same place where you were raised, and because of that you develop some of the same environmentally determined traits - is that the same as "passing on" those traits? You could argue that. But the point is, when there is no more link to the genes - evolution can't act. Natural selection can't act. Evolution is a process that happens to genes.

Edit: let me see if I can help clarify things for you a bit. Natural selection requires variation to act on. Where does that variation come from? It is not acquired by the parents. What happens is that variation is created in the process of reproduction. The formation of egg and sperm cells, through mutation and recombination, results offspring that are all different from one another, that all have variation. Then, those that have the best variations suited to their particular environment have more offspring than those that do not. That is how adaptation occurs. None of the variation is acquired during the lifetime of the parent, it is done in the process of having offspring which results in varied offspring. Does that help?

I understand that, but the explanation avoids the mechanism of mutation in response to environment. Is this not an important evolutionary mechanism? Although the parent may not acquire a characteristic in its lifetime as the result of its environment, as you said, it will surely pass on in its sperm or egg the influence of such factors? Is this not correct?

The variation you speak of that arises and is best suited for the environment, and thus prized for natural selection, is the result of mere chance of the combination of genes? Isn't variation directly influenced by an organism's environment?

To make an example on what you're saying, although which surely may sound like a clumsy extrapolation:

Why is it that parents of a certain ethnic population cannot produce a child that does not share the physical characteristics of their own gene pool?

Originally Posted by twainmane

To make an example on what you're saying, although which surely may sound like a clumsy extrapolation:

Why is it that parents of a certain ethnic population cannot produce a child that does not share the physical characteristics of their own gene pool?

The environment would have little directed effect on the gametes of a human being.

Genetic change occurs slowly in humans, only a few mutations will be carried on in the gametes, and most will not have a noticeable effect on physical characteristics.

If time is held indefinitely, and you were to place a group of people from perhaps Africa or Eastern Asia in Northern Europe, would they evolve characteristics that are shared amongst current populations that live there?

Originally Posted by twainmane

If time is held indefinitely, and you were to place a group of people from perhaps Africa or Eastern Asia in Northern Europe, would they evolve characteristics that are shared amongst current populations that live there?

It is a complicated question. There are many things to consider, not the least of which is sexual selection. Others are the exact environment they are in, what kind of competition they would encounter, what food is available, etc. Today they would probably just mix into the population, but if they did the original migration again, chances are they'd end up the same as they have I'd say.

Originally Posted by twainmane

I understand that, but the explanation avoids the mechanism of mutation in response to environment.

Organisms do not mutate in response to the environment. Mutation is an error that can potentially occur every time DNA is copied. The only way you could potentially argue that mutation occurs in response to the environment is that certain organisms have evolved more error prone DNA copying proteins than others, because more errors leads to more variation which allows for more varied offspring, increasing the chances that at least one of the offspring will have a variation that will be advantageous in the environment. This is common in bacteria and viruses, for instance, to allow them to quickly adapt around their hosts' defenses.

However, it's not as though one organism suddenly "decides" that it needs to have more mutations in this batch offspring so it induces a higher mutation rate in its current egg/sperm production, etc. Within a given species mutation rates are constant from generation to generation (unless they themselves are being actively selected upon).

What responds to the environment is not mutation, but which variations (created by mutation) survive and reproduce and which do not. That variation, however, is random and unpredictable. This is why fast changes in the environment tend to kill some species; if the species doesn't luck out soon and happen to generate offspring with a mutation that will allow them to handle the new environment, they all die.

If time is held indefinitely, and you were to place a group of people from perhaps Africa or Eastern Asia in Northern Europe, would they evolve characteristics that are shared amongst current populations that live there?

We can only be reasonably sure that they would develop the same characteristics that significantly improved reproductive success in that particular environment in the original group. And even then, because mutation is random, they may not find the same "solution" to the same environmental problems as the original population did. Many of the neutral variations between human populations can be attributed purely to chance (as a result of population history), and so it's a total crapshoot if those characteristics would independently appear again.

How is it then that human populations have acquired such distinctive and constant characteristics? The example of blond hair as being a 'native' attribute of populations in northern europe (although not constant as the epicanthic fold is in East Asia) would mean it's a biological trait particular to a certain environment, is that not correct?

Originally Posted by twainmane

How is it then that human populations have acquired such distinctive and constant characteristics? The example of blond hair as being a 'native' attribute of populations in northern europe (although not constant as the epicanthic fold is in East Asia) would mean it's a biological trait particular to a certain environment, is that not correct?

Not necessarily, no. Human population history is full of bottlenecks - that is, the population shrinking down to a very small number, and then the numbers growing until they are as high as they are today. When a bottleneck happens, this removes a lot of the individuals in the population - removing some genetic variation. If there is a certain rare allele which is only present in a few people, significantly culling the population could cause the loss of those individuals and of the alleles they carry. And when the population is small, genetic drift can also play a large role. When there's only a few individuals reproducing, by random chance an allele the one of the parents has might never get passed down to one of the children.

The result of these processes is that a trait with multiple variations might lose some of those variations due to the bottleneck, resulting in a population with just one variation. Then the population grows to large numbers and everyone has that one variation.

This is why, when testing to see if a certain trait was ever favored by natural selection in the past or now, you need to assess the population history and see if any random processes like these may have occurred that could create the same signal as natural selection does. And if they have, prevalence alone will not give you the answer. You have to look for more information to figure out what happened.

I think I understand what you're saying Paralith. Thanks for your replies. My last question is, why isn't there such random mutation amongst human populations today? Kids look like they're parents, wherever they're brought up.

If we Americans continue a relatively balanced outdoor life will we show random mutations characteristic of Native Americans?

Originally Posted by twainmane

I think I understand what you're saying Paralith. Thanks for your replies. My last question is, why isn't there such random mutation amongst human populations today? Kids look like they're parents, wherever they're brought up.

Perhaps I misunderstand you, but of course random mutation is happening today. So is recombination. Kids resemble their parents but they don't look like their exact twin, do they? Think about the many, many people that are born with a congenital disorder of some kind. Those are random mutations. However there are many more random mutations that exist in our neutral DNA, DNA that doesn't code for any phenotype. Mutations can arise there over and over again and you could never tell just by looking at the organism.

If we Americans continue a relatively balanced outdoor life will we show random mutations characteristic of Native Americans?

The point of random it is unpredictable and undeterminable. If I roll a dice once, should I expect to roll the exact same number every subsequent time I roll it as long as I'm still sitting at the same table? Of course not.

I was referring to random mutations concerning hair color, skin color, and other physical characteristics. I've never heard of someone who has a random mutation on the scale of the mutations that had occurred when human populations began to diverge.

Originally Posted by twainmane

I was referring to random mutations concerning hair color, skin color, and other physical characteristics. I've never heard of someone who has a random mutation on the scale of the mutations that had occurred when human populations began to diverge.

How do you know that the traits which we may now see only in certain populations, due to drift and bottlenecks, were not present in the ancestral population? When did blond hair first emerge in the hominid line? Were there blonde Homo erectus? We don't know. I think you may be making an inappropriate comparison;what is "today" to you? The past 100 years? The past 500 years? As a species we likely emerged nearly 200,000 years ago. If you count us as continuous with Homo erectus, and some do, we emerged nearly 2 million years ago. So, should you be surprised that there haven't been as many obvious physical mutations in humans in the last 500 years as there have been in the last 200,000 years? In the last 2,000,000 years?

Originally Posted by twainmane

I was referring to random mutations concerning hair color, skin color, and other physical characteristics. I've never heard of someone who has a random mutation on the scale of the mutations that had occurred when human populations began to diverge.

How big are those differences really though? I always like to use dogs as an example. Look how much they have diverged from their wolf ancestors. They are certainly much more divergent than we are (at least physically). Humans selectively bred them towards certain traits, while in nature that is done by sexual selection, etc. With the added help of bottlenecks, as paralith explained, it becomes much easier to see it happening, at least for me.

Let's be honest with each other now.

The greatest recent morphological change in some human populations is an great increase in height.

It's not genetic.

It's environmental.

We are more than just genes.

Of course not. But natural selection requires heritable variation in order to work.

Natural selection doesn't work. Natural selection is.

Why is that we don't see any random mutation to red or blond hair in people outside of Europe , or rather, to parents without any ancestry of either characteristic?

Is this not how it's hypothesized? That light hair color came about as a random mutation, and was then facilitated by natural selection to reach its current preponderance?

If certain physical characteristics are not caused in response to their environment, why is that we don't find people that look (of a 'vestigial' degree) European in Africa, Japanese in Europe, and so on? And while I understand you'll say our distinctive phenotypes are highly specialized over a long periods of time for their traits that happen to be suitable for their respective environments, it doesn't exactly explain it.

It's widely held that our original ancestral population, after shedding most of its hair, became uniformly dark-skinned in Africa. And then as a population not too different looking than the continent's current populations there went on to populate the rest of the planet.

Originally Posted by twainmane

Why is that we don't see any random mutation to red or blond hair in people outside of Europe , or rather, to parents without any ancestry of either characteristic?

We do. In its extreme form it's albinism, but populations outside Europe nevertheless do on occasion propoduce children with differing hair colours, and characteristics not evident in the parents.

Originally Posted by twainmane

Is this not how it's hypothesized? That light hair color came about as a random mutation, and was then facilitated by natural selection to reach its current preponderance?

Natural selection, or in the case of human morphological difference amongst populations, possibly even a form of sexual selection (a special type of natural selection driven by mate choice issues).

Originally Posted by twainmane

If certain physical characteristics are not caused in response to their environment, why is that we don't find people that look (of a 'vestigial' degree) European in Africa, Japanese in Europe, and so on? And while I understand you'll say our distinctive phenotypes are highly specialized over a long periods of time for their traits that happen to be suitable for their respective environments, it doesn't exactly explain it.

It's widely held that our original ancestral population, after shedding most of its hair, became uniformly dark-skinned in Africa. And then as a population not too different looking than the continent's current populations there went on to populate the rest of the planet.

You need to refer back to paralith's post about bottlenecks.

You may start with black skinned people in Africa, but early on populations of humans were often isolated and culling happened quite frequently. So, it was easy for certain traits that don't are not selected for by natural selection to become prominent in one population but not in another. Also, you should wiki genetic drift.

In small isolated populations genetic drift can result in some phenotypes becoming more prominent without the need for selection.

http://en.wikipedia.org/wiki/Genetic_drift

As to evolving the same traits, this is unlikely.

Skin colour doesn't seem to be a good example of this, some theorize light skin is selected for by low levels of sunlight, since you need lighter skin to get the same amount of vitamin D. It is selected against in higher levels of sunlight by it being easier to burn and lose moisture. In North America, the Inuit have much lighter skin than the natives of southern Canada and the USA. They've also retained several typically Asian characteristics. So, natural selection may play a small part of this, or it could be accounted for by them having less time to develop distinctly Inuit physical characteristics.

http://cogweb.ucla.edu/ep/Frost_06.html

I quite liked this little article on eye and hair colour.

Originally Posted by twainmane

If certain physical characteristics are not caused in response to their environment, why is that we don't find people that look (of a 'vestigial' degree) European in Africa, Japanese in Europe, and so on? And while I understand you'll say our distinctive phenotypes are highly specialized over a long periods of time for their traits that happen to be suitable for their respective environments, it doesn't exactly explain it.

I really like that link tired_sleepy gave on hair and eye color. Addresses it very nicely. But also like tired_sleepy I again want to emphasize the bottleneck issue. Genetic evidence suggests that this type of thing happened often as modern humans spread out across the world. One small piece of an originally larger population goes off on it's own (bottlenecks), struggles for a while as a small group, experiences drift, and then expands into a large population all of which share those few traits that were present in the original group.

I have a feeling you may also be underestimating the variation that exists within broad geographical areas. Different ethnicities on the continent of Africa differ more from each other than do all the different ethnicities in Europe. This is because, since the modern human species emerged in Africa and then spread out, the populations that stayed in Africa are the oldest and have had the longest amount of time to develop new mutations and diverge from each other. And again, just because the mutations and differences are not extremely obvious in their physical appearance doesn't mean they're not there. And even though Europeans are less genetically diverse from Africans there is still diversity; if you go into Asia, they don't all look identical, that is a huge area and there are myriad variations across it. A recent genetic study I read has found at least 17 genetically distinct lineages on the Asian continent.

Based on what we know, the entire population of Europe began from a handful of albinos begot from dark-skinned parents, is this not correct?

I mean, just try to picture that all of our European ancestors descended from a few people who carried this random mutation. Is this possible?

Just picture the rate of albinism or such physical mutations we see around us today. Pretty rare. And ontop of it, human populations were exponentially smaller at the time we expected Europe to be populated.

How is it that a handful of albinos, begot from small human tribes who at the time were attempting to habitate Europe (but unsuccessfully, because their dark skin led to rickets in a sunless environment) actually managed to find each other and to create from their small gene pool Europe as it is today?

Originally Posted by twainmane

Based on what we know, the entire population of Europe began from a handful of albinos begot from dark-skinned parents, is this not correct?

I mean, just try to picture that all of our European ancestors descended from a few people who carried this random mutation. Is this possible?

Just picture the rate of albinism or such physical mutations we see around us today. Pretty rare. And ontop of it, human populations were exponentially smaller at the time we expected Europe to be populated.

How is it that a handful of albinos, begot from small human tribes who at the time were attempting to habitate Europe (but unsuccessfully, because their dark skin led to rickets in a sunless environment) actually managed to find each other and to create from their small gene pool Europe as it is today?

My goodness twain, who ever said that the whole of the European continent are albino? They are not. What happened was that those individuals who happened to have lighter variations in skin color than others had more offspring, and over time the individuals with lighter colored skin outnumbered the individuals with darker colored skin. When you're talking about a trait that is adaptive it doesn't follow the same patterns as traits that are neutral. Skin color is probably an adaptive trait, whilst many other differences between ethnicities probably are not.

Why would skin color necessarily be an adaptive trait?

Originally Posted by spuriousmonkey

Why would skin color necessarily be an adaptive trait?

Not necessarily, but current evidence suggests it's possible. It doesn't follow the same pattern as worldwide neutral genetic variation so it's probably not completely neutral and it grades at a linear rate from darker to lighter the further you go from the equator.

I think the chances it is due to sexual selection is much higher to be frank.

Paralith, I'm sorry if I used the wrong term. Of course not I'm referring to actual albinism, as we know it. I used the term because the original inhabitants of Europe were probably dark-skinned and for them to have created populations of a drastically different skin color it would have had to begun in the same manner as we've discussed, as a random mutation. In the same manner albinism occurs in populations in Africa today. Do you follow that?

It would have to be supposed that the original and few dark-skinned inhabitants of Europe begot offspring, in the same manner and rate as we beget a child of albinism or other physical mutation, which from their small handful went and found each other to create Europe as it is today.

Would two albinos have an albino child?[/b]

Originally Posted by twainmane

Paralith, I'm sorry if I used the wrong term, of course not I'm referring to actual albinism as we know it. I used the term because the original inhabitants of Europe were probably dark-skinned and for them to have created populations of a drastically different skin color it would have had to begun in the same manner as we've discussed, as a random mutation. In the same manner albinism occurs in populations in Africa today. Do you follow that?

It would have to be supposed that the origina and few dark inhabitants of Europe begot offspring, in the same manner and rate as we beget a child of albinism, and then from that selective handful created the populations that reside there today. Is this wrong?

Considering the way we know skin color is inherited, yes. Skin color is a pleiotropic trait - there are many genes that affect it. The result of this is that depending on which alleles for which genes get passed on to your offspring, you can have offspring with a range of skin colors that are not exactly like your own. Over time those offspring that were a little lighter did a little better, and passed on more of their genes, so more and more of the lighter skinned alleles began to accumulate in the population.

Here is a fairly detailed explanation of the genetic of human pigmentation. This isn't a simple one-gene-one-trait issue.

What is wrong with both soft and hard working side by side? Why are they so disputed?

In plants it doesn't take a very long time for adaptations to appear. Those adaptations each evolved from parent to parent. Hard evolution is a sum of much soft evolution no?

Originally Posted by marcusclayman

What is wrong with both soft and hard working side by side? Why are they so disputed?

In plants it doesn't take a very long time for adaptations to appear. Those adaptations each evolved from parent to parent. Hard evolution is a sum of much soft evolution no?

Because it's Lamarckian evolution, we simply do not pass on aquired traits in that way.

Originally Posted by marcusclayman

What is wrong with both soft and hard working side by side? Why are they so disputed?

In plants it doesn't take a very long time for adaptations to appear. Those adaptations each evolved from parent to parent. Hard evolution is a sum of much soft evolution no?

Here's the gist: when it comes to genes, traits acquired by parents are not passed on to offspring. Natural selection only happens (is that ok spurious?) to traits that are heritable, that get passed on. If this is what is meant by "soft" selection, then it never occurs and is fallacious.

Now there is some evidence that information about the environment may get passed to offspring through epigenetic means like DNA methylation - but the ability to do those things is still genetically enabled, allowing these processes themselves to be subject to natural selection.

The reason for those born with the mutation of lighter skin fared better in the northern european clime is because of the biological necessity for Vitamin D--is this correct? Lighter skin facilitates faster Vitamin D production in the sun as opposed to darker skin (which is thought to be an adaptive trait to protect the deleterious effects of a harsh sun climate). Vitamin D is very interesting..

Obviously lighter skin colour isn't a matter of one random mutation.

Otherwise we would all be black and white.

I think I get it, not really. How does an environment change the genes of a parent without changing the parent? Is my concept of genes completely wrong? I don't know much about it, I'm sure you could gather that for yourself.

Originally Posted by twainmane

The reason for those born with the mutation of lighter skin fared better in the northern european clime is because of the biological necessity for Vitamin D--is this correct? Lighter skin facilitates faster Vitamin D production in the sun as opposed to darker skin (which is thought to be an adaptive trait to protect the deleterious effects of a harsh sun climate). Vitamin D is very interesting..

Yes twain, that is the hypothesis. There may not have been many mutations involved either if, as I described, the gene suite already had the ability to result in lighter variations. But it still remains to be further tested and researched until we're sure. My opinion is that the evidence supports it fairly well, but obviously others like Spurious aren't convinced. So we'll see.

Originally Posted by marcusclayman

I think I get it, not really. How does an environment change the genes of a parent without changing the parent? .

Ever heard of germline and somatic cell line?

Originally Posted by paralith

Originally Posted by twainmane

The reason for those born with the mutation of lighter skin fared better in the northern european clime is because of the biological necessity for Vitamin D--is this correct? Lighter skin facilitates faster Vitamin D production in the sun as opposed to darker skin (which is thought to be an adaptive trait to protect the deleterious effects of a harsh sun climate). Vitamin D is very interesting..

Yes twain, that is the hypothesis. There may not have been many mutations involved either if, as I described, the gene suite already had the ability to result in lighter variations. But it still remains to be further tested and researched until we're sure. My opinion is that the evidence supports it fairly well, but obviously others like Spurious aren't convinced. So we'll see.

It really doesn't matter why it took hold. Of most traits we do not know. Mostly because the original adaptation often isn't the current adaptation any more.

That's life.

Originally Posted by marcusclayman

I think I get it, not really. How does an environment change the genes of a parent without changing the parent? Is my concept of genes completely wrong? I don't know much about it, I'm sure you could gather that for yourself.

marcus, for the most part, the environment does not change genes. As I've mentioned once already in this thread, mutations are the result of accidents during the normal process of copying DNA strands so that a cell that is splitting in two will make sure each new daughter cell has the DNA it needs. This is an entirely random and unpredictable process. Now, I said "for the most part" because sometimes things like radiation or excessive UV exposure can also cause mutations - but just like the copying mistakes, these mutations are random.

Like spurious said, you can think of an individual having two lines of cells. One line is the somatic cells - these are all the cells in your body. The other line is the germ cells. These are the cells which will become eggs or sperm when it's time to reproduce. These cells do not affect the functioning of any of the somatic cells - you can almost think of them as little half-pieces of offspring that the parent is holding inside itself until the time is right. When these cells are made into eggs and sperm they are split multiple times and in this process of splitting some of those copying errors happen. Then if everything goes well they merge with the egg or sperm of another person and offspring growth begins.