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This question already has an answer here:

The following is an wikipedia article on Lamarckism.

https://en.wikipedia.org/wiki/Lamarckism

According to Ernst Mayr, any Lamarckian theory involving the inheritance of acquired characters has been refuted as "DNA does not directly participate in the making of the phenotype and that the phenotype, in turn, does not control the composition of the DNA."[75] Peter J. Bowler has written that although many early scientists took Lamarckism seriously, it was discredited by genetics in the early twentieth century.

The evolutionary biologist T. Ryan Gregory contends that epigenetic inheritance should not be considered Lamarckian.

It seems to me that the assertion that acquired characteristics can be inherited was denied by the modern synthesis theory of evolution. Is this true? If yes, what is the reason of the denial?

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marked as duplicate by Remi.b, James, Amory, The Last Word, Chris Nov 18 '15 at 19:40

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

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    $\begingroup$ Where did you hear it? $\endgroup$ – Chris Nov 14 '15 at 10:42
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    $\begingroup$ Answered before searching the site. Might be a duplicate of biology.stackexchange.com/q/884/19650 $\endgroup$ – YviDe Nov 14 '15 at 10:50
  • $\begingroup$ @Chris Please read my new edit to the question. $\endgroup$ – Makoto Kato Nov 22 '15 at 5:01
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Generally, yes, this is not part of theory of evolution as it is generally accepted by most of the scientific community.

For a trait to be subject to natural selection over several generations, it needs to have heritability, meaning it needs to show up in offspring (or their offspring). Generally, what is called an "acquired trait" does not fit that criterion. What's passed on is the genetic material of the parents and that doesn't change when the parent acquires these traits.

For example, bonsai trees are kept small by environmental conditions, as such, their height could be called an acquired trait. Their offspring does not naturally grow as a bonsai tree. Giraffes did not grow longer necks because they stretched them, but because those giraffe ancestors with longer necks (which just happens randomly through mutation - you have varying neck lengths in a population) could reach food more easily and could survive when those with shorter necks didn't. The giraffe example is a classic one that was proposed by Jean-Baptiste Lamarck, whose theory of evolution (called Lamarckism) was superceded by Darwin's.

There are traits where acquired versus genetic traits are hard to differentiate - while a good athlete does not have children who are athletic because their parent did sports, they are often also good athletes. For one thing, the parent might be genetically "suited" for sports and has passed these genes on. Another reason is that they will probably train their children and want them to become more athletic.

I know of one example where something that could be called an acquired trait is passed on to offspring - methylation patterns. Those are modifications of the genetic material that happen during an organism's lifespan and aren't modifications of the actual genetic code - they can be passed on to offspring. Since these patterns influence gene expression, they have an effect on the offspring. However, that's usually not what people mean when they talk about acquired traits.

Lamarckian inheritance

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  • $\begingroup$ It's worth pointing out that popular conceptions of epigenetic inheritance (methylation patterns) are wildly out of line with the actual science. Popular media have spread the notion that epigenetic change is much more powerful, long-lasting, and widespread than it actually is; in reality epigenetic inheritance is rare in general, typically has little impact, and even when it does occur generally fades before it can impact evolution significantly. People who read popular science often believe that Lamarckian evolution has been supported, a view that isn't supported by the actual evidence. $\endgroup$ – iayork Nov 15 '15 at 13:54
  • $\begingroup$ What about the hologenome theory? The hologenome theory of evolution contains Lamarckian aspects within a Darwinian framework. ncbi.nlm.nih.gov/pubmed/19573132 $\endgroup$ – Makoto Kato Nov 21 '15 at 18:25

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