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Background Information

As we all know, life as we know it today is caused by the process of natural selection, sometimes referred to as survival of the fittest, as proposed by Darwin. Essentially, the organisms better at surviving would be more likely to pass on their genes.

Before Darwinism became widely accepted, Lamarck proposed a similar theory. The following picture describes it perfectly (with the example of a giraffe):

Lamarck's Theory of Evolution

The difference between his and Darwin's theory is that he believed that a traits acquired in the lifetime can be passed on.

Question

Could life as we know it arise if Lamarck's theory was correct rather than Darwin's?

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No

The giraffe neck is a commonly given example, but there are lots of features of Lamarckian evolution that exclude it from being a possible explanation of the origin of species.

"Inheritance of acquired traits". One version of Lamarckian evolution imagines a blacksmith. He uses his arm muscles, which respond by growing larger. His children are then born with naturally larger muscles... However many of my acquired traits are damage. For example I have sun damaged skin, if this trait were passed on, my descendents would have more damaged skin from birth. For Lamarckian evolution to a possible, there would need to be a mechanism for distinguishing "good" acquired traits from harmful ones

"Striving". A proposed solution to this is that only traits which are acquired through effort or choice are transmitted down the generations. While it is reasonable to imagine a Giraffe striving to reach leaves, it is not a solution for how sight could evolve (trying to see doesn't improve your sight) nor can it explain evolution in plants or simple animals (a plant doesn't strive to photosynthisise)

"Reductionism". The mechanism of Lamarckism would be hopelessly complex. It would require the animal to have a mechanism to analyse its current state, and then rewrite its DNA in order to reproduce.

There is evidence that there is non-genomic transmission from mother to child through the womb, this cannot explain the origin of species.

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  • $\begingroup$ let me start with a reminder that lamarckian evolution is otherwise identical to darwinian; the difference being that non-genetic traits are still passed down. first, there already is a mechanism to distinguish trait viability: natural selection. if having sun-damaged skin results in you not being able to find a mate, than that trait is selected against and will not become common across the rest of the species. two, random mutations still take place, so the appearance of eyes could still result form chance. finally, this system presumably gets rid of DNA and genetic encoding along with darwin. $\endgroup$ – Duncan Urquhart Feb 29 '16 at 21:46
  • $\begingroup$ The question asks "if Lamarck's theory was correct rather than Darwin's". So that implies that in this world natural selection (Darwin's theory) does not operate. Its Lamarck instead of Darwin, not Lamarck alongside Darwin. As I noted, there is non-genomic transmission of some characteristics from mother to child, but my answer to the question remains: In a (magical) universe in which Lamarck not Darwin is correct, life does not evolve. $\endgroup$ – James K Mar 1 '16 at 17:09
  • $\begingroup$ i am not an expert and do see what you mean, but i think that lamarckism has to acknowledge random mutation. i understood that the main difference between the theories was that darwin said that random changes drove the development of life, whereas lamarck said that it was environmental adaptation. it seems like both of these theories should allow for mutation, the difference being what the root cause of positive improvement and advancement; again, however, this could be wrong. if it is, than i believe you would be right about the natural creation of life being impossible. $\endgroup$ – Duncan Urquhart Mar 1 '16 at 17:27
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So summed up, evolving is now instead of: "sorting (live/die) of a random variation" consists of the body adjusting to behaviour caused by will, caused by a "need". That may even to some extent be correct, as training your body is essentially to change its form through new behaviour.

A problem then arises: "How is this new form transferred to the next generation?" This is at least partly possible through gene activation. That is, what genes are active and affects the shape of the giraffe is not directly possible to read out from the DNA, the "source code". DNA is packed together, and the way is it packed affects how active different genes are. The proteins packing the DNA is of course also coded in it, but exactly what packaging-proteins that are active are affected by... the packaging. Recursively, this means that not all information in the system is recoverable from the base pairs alone. (mutations and actual changes in the DNA is necessary in the long run though. Darwin's theory is a must then, as Lamarck does not cover the concept)

But Lamarckian evolution evolution also includes one more component: Intelligence. A giraffe not longer reaching the leaves, knows that it much stretch. In contrast, a bacteria no longer reaching its source of food simply dies. Evolving is then back to Darwin's variations and sorting. One can therefore say that Lamarckian evolution is possible, and even actually present, but only in high-complexity systems. That means, to just pin down the point, Lamarckian evolution can not explain how complex organisms originally evolved, leaving it insufficient.

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  • $\begingroup$ And of course, life didn't start out as highly complex organisms, so how would we have gotten from the starting point to where we are now? It's a recursive line of reasoning all over again, recursively. $\endgroup$ – a CVn Feb 28 '16 at 15:14
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As always, I love world building questions which try to explore some novel approach to life, only to find that nature has already found a way. It's marvelous what nature can do.

Lamarkian evolution actually does happen, to some degree. While much of our genetic evolution is very Darwinian, there are plenty of example of extended phenotypes which get inherited from the mother in utero. Many traits of a child find their origins in mother's choices while pregnant. Your baby's sense of taste, for example, gets partially developed from the mother's diet. Live in a part of the world where eating garlic is essential for life? Your child will actually pick up a taste for garlic from the amniotic fluid it lives in, long before it ever sees the bulbous herb.

Perhaps a love of garlic isn't exactly a life skill, but other traits that operate this way are very valuable. For instance, it has been found that a baby reacts to mother's stress hormones in utero. If mommy has found that the only way to cope with the harshness of life is through the stress hormones like cortisol (which tune the body to face the stress), the baby will develop to generate more cortisol in stressful situations and decrease cortisol slower after the stress is removed. This has actually been measured, correlating maternal cortisol levels during pregnancy to cortisol levels produced during the baby's first blood draw.

Sound harsh? Maybe not. One of the known effects of cortisol is a decreased immune system, and worse allergic reactions. These sound useless right? Maybe not. Biochemically, it suppresses outputs of Th1 helper T cells, while activating Th2 cells to encourage them to produce more output. As it turns out, Th1 cells are primarily involved in fighting bacterial and viral infections. Th2 is more involved with our defense against extracellular parasites like worms. Now we don't have many worms in our modern 1st world life, so we don't benefit much from Th2 upregulation. However, if you are living in a part of the world where worms and other parasites are a regular part of life, this response is very useful.

So we have an example of Lamarkian evolution, at least at an extended phenotype level. If mother deals with a lot of worms in her life, her cortisol levels will tend to be higher. The child will then develop accordingly, and be born more ready to deal with the infectious world around them than they would have been if mom didn't stress her body. And likewise, if the baby is a girl, it is likely that her stress levels will be passed to the next generation.

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  • $\begingroup$ As an aside, in this strange world where anything is possible, there are a few species of bacteria which actually stimulate the hypothalimus to emit cortisol to downregulate Th1 operation. The world really is an amazingly exotic place. $\endgroup$ – Cort Ammon Feb 28 '16 at 4:34
  • $\begingroup$ Epigenetics is not actually evolution, in that it does not create any new genes. What it does, is condition the inherited genes to be more or less active in the developing child. There are things here not yet well understood. One would expect better nutrition in the womb to program a child to grow taller. In fact it takes another generation. The first well nourished generation doesn't grow taller on average than their parents but the second generation does grow taller than their grandparents! $\endgroup$ – nigel222 Feb 28 '16 at 16:21
  • $\begingroup$ @nigel222 If you choose to narrowly define evolution as only processes which directly modify the deoxyribonucletic acid strands in gamete cells, then you are right. If you, instead choose to define it as a process which allows offspring to be more fit in their environment, such "evolution" becomes useful. Fortunately for us humans, it appears natural selection is not very strict in the definitions it uses =) And it seems very reasonable to me that epigenetics may want to "observe" a few generations before committing any associated genetic changes to the record. $\endgroup$ – Cort Ammon Feb 28 '16 at 16:29
  • $\begingroup$ For instance, our stress levels are not fully defined by the mother. Some of their behaviors are in the DNA. The maternal functionality may help the next generation be fit, and over time, if that stress level continues to be valuable, genetic mutations may develop to make it easier to achieve that stress level. So, in that light, perhaps such epigentetics is actually the first layer of evolution, and the genetic material shifts which are well described by Darwinian evolution are merely the last. $\endgroup$ – Cort Ammon Feb 28 '16 at 16:31
  • $\begingroup$ (I just like to shake up definitions. Nature presents so many continuous systems which we like to think of as discrete because it makes our lives simpler. Sometimes its fun to try to bring the whole system into perspective, and see it for the beautiful continuous process it is) $\endgroup$ – Cort Ammon Feb 28 '16 at 16:32
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Yes

My answer is short and simple, because this question doesn't really need a long answer. Your question is like asking, if Prometheus really created humanity, could humanity exist? The answer is obviously yes. These theories were designed to explain why the world is the way it is. If it is proven correct, then the world isn't suddenly and irrevocably changed, it just remains the way it is.

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    $\begingroup$ Now, If you were to change your question to, "How would it be possible for life to evolve according to Lamarck's theory?" then Hohmannfan's answer would be superior and mine would be invalid. If you were to ask, "How would life change in the future?" It would be a completely different question. $\endgroup$ – Xandar The Zenon Feb 28 '16 at 3:14

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