I'm a student in biology and just recently learned about Lamarck's theory on evolution and how it has been disproved. While I understand that you cannot alter your genes, I'm still having a hard time understanding some parts of it, mainly how inheriting strength (such as working out) will not be passed down to my offspring. If someone was obese, exercised to the point of no longer being obese, will this person's offspring still start off as obese?

  • $\begingroup$ You inherit genes for muscle from your parents. What you do with that muscle is not passed on. Your physical attractiveness if you work out may benefit you passing on your gene pool, but that's about all you can do genetically. Obesity may have something to do with gut flora, which can be traded between two individuals, e.g. from mother to offspring. But there is much to obesity which is not understood yet. $\endgroup$ – anongoodnurse May 20 '17 at 1:16

Indeed, whether you work out or not will not change how strong your offspring will be. This is exactly why Lamarck's was wrong.

I would note however that Behaviour can be heritable and Your behaviour can affect your kids environment

Behaviour can be heritable

The probability of you working out is affected by your genes and so if you have a genetic predisposition for willing to work out, this will be passed on.

Assuming there are genetic predisposition for liking to work out, the fact that you worked out would not increase the probability of your kid to work out via genetic inheritance but the fact that you have a genetic predisposition for liking to work out will increase the probability that your kid will have the same preference and will work out

By the way, if you want to learn more about the concept f heritability you should have a look at Why is a heritability coefficient not an index of how “genetic” something is?

Your behaviour can affect your kids environment

Working out won't affect your genes but it will likely affect the environment in which the kid will grow. Here are three examples

  1. Teaching

If you eat healthy, you will probably teach your kids to eat healthy too.

  1. Womb environment

Also, if you eat healthy and are a woman, you will likely give the right nutrients to your offspring while still in the womb (assuming you are a lady).

  1. Epigenetics

Your environment will cause epigenetic changes (changes not in DNA but in the very close environment of the DNA such as typically histone tail methylation). These epigenetics modifications will be directly passed to the foetus.

More information

A post your question is almost a duplicate of...

A post on heritability

And finally an answer that talks about non-genetic inheritance

  • $\begingroup$ "...the fact that you have a genetic predisposition for liking to work out will increase the probability that your kid will have the same preference and will work out..." Can you please support this with a reference? I.e., is there any evidence that points to a genetic predisposition to work out? $\endgroup$ – anongoodnurse May 20 '17 at 1:18
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    $\begingroup$ I added Assuming there are genetic predisposition for liking to work out [..]. My goal was to explain the basics of inheritance, not to review the heritability of specific trait. Thanks for noticing this potential confusion. I would notice however that given there is very likely heritability for such life style given that many of hormones concentration are heritable (incl. testosterone typically). $\endgroup$ – Remi.b May 20 '17 at 1:22
  • $\begingroup$ There's no evidence that I'm aware of that testosterone levels contribute to a propensity to work out. A propensity towards some things (like hostility, aggression, etc.) but exercise, again, not that I'm aware of. $\endgroup$ – anongoodnurse May 20 '17 at 1:38
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    $\begingroup$ It is pretty tough to investigate liking independently of an environmental context and of abilities (as many physical properties relating to sport abilities being heritable) but anyway.... it really is not the point of the question nor of the answer. But thanks for clearing the possible confusion. $\endgroup$ – Remi.b May 20 '17 at 1:43
  • $\begingroup$ Also not that it has recently be shown that learned behaviour can be inherited through epigenetic mechanisms. Mice born to parents that were conditioned to fear a certain smell, still reacted to that smell despite never being conditioned (see news article or original paper) $\endgroup$ – Nicolai May 30 '17 at 4:58

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