How does evolution account for new body parts?

I think the above comment raises a potentially valuable teaching point. How have new body parts arisen over the course of the history of life on this planet, according to the theory of evolution? I’d be interested to hear from people who do not accept that this account can be verified (i.e. creationists) as well as from those who accept evolution.

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The first question we have to ask is what counts as a new body part or new organ? For example, at what point does a fish fin stop being a fin and become a leg? Are tetrapod legs new? If we watched the slow development of a nervous system from a dispersed network to a centralized ganglion to a well developed brain, at which point is the brain a new organ?

Not to trivialize your point, but to avoid getting lost in the weeds, I think we can agree that something like, say, the human hand could be considered a “new body part” in the sense that it now exists, and did not exist in the Precambrian, say. Now, of course, that does not mean that a structure ancestral to the human hand did not exist among Precambrian biota. But the hand itself did not.


That was my first though too. What qualifies as “new”? Every body part we have evolved from earlier simpler precursor parts possessed by our distant ancestors. The classic teaching example is the evolution of mammals evolving their ear bones from the jawbones of their synapsid ancestors.

Evolution of the mammalian middle ear and jaw: adaptations and novel structures

Here are some variations of fins from lobe-finned fish, both extant and extinct:


Then we have the tetrapod intermediates:



It might be helpful if ID/creationists could point to a specific point where the hand first emerges.


Yes. But there seems to be some disagreement over the details of the process, as it would occur if evolution was true. For instance, in the passage I quoted, @scd suggests that we should be seeing human beings walking around today with “new body parts” that did not exist before.

@scd must also think that he can sit at a construction site and watch the construction of an entire skyscraper, from start to finish, in under 30 minutes.

In that case, however, there would be new parts fabricated and added to the structure. So I don’t think timescale is the main issue here.

90% of our skeletal anatomy can be found in Devonian fish



I think we should not pick on people BEFORE they arrive in the discussion. There is plenty here to discuss without starting the usual fight. :wink:

That image reminds me of The Creature From The Black Lagoon! :laughing:

I can’t get the Discourse Software to display the username from the quotation in the OP so I will simply copy it:

. . . and we never seen someone who evolve say a new organ part like a part of a wing or a new part of an eye etc.

My first thought is that individuals (i.e., “someone who…”) don’t “evolve” things. Populations over generations evolve changes in allele frequencies, some of which are eventually manifested in new structures.

Also, if we allow for such a general and non-technical application of the verb “to evolve”, then I would assert that we OFTEN observe individuals evolving [grimace] “a new organ part”. For example, I “evolved” an accessory muscle in my arm. It was discovered during an ulnar nerve transposition surgery. The surgeon removed the extra muscle so that it wouldn’t put pressure on the ulnar nerve. He says that he comes upon such novel body structures not all that rarely in the course of his weekly surgery schedule. In one case the year before he said he removed an accessory muscle (i.e., a muscle that one wouldn’t normally expect to find) from a large man which filled up the tissue tray to where it looked like a quarter-pounder hamburger.

He explained that accessory muscles arise for a variety of genetic and embryological development reasons and that a mutation arising during the formation of my genome could be the explanation of my extra body part. Now imagine if that extra muscle gave me some sort of beneficial survival advantage and I passed on that mutation to my descendants. You can also imagine such a mutation having no survival advantage but simply multiplying in a population by sheer roll of the dice. Either way, I would assert that the “new organ part” challenge of the OP would be met and satisfied.

This raises an important point that I see IDcreationists often don’t properly consider, which is that things used to be different. It also relates to the pseudo-problem of irreducibly complexity.

The idea often seems to be that some fellow can’t imagine how X could have evolved, because what good would “half of X” be? Invariably it turns out there was never “half of X” in the first place, rather X evolved from some other thing Y that performed a related but slightly different function.

Whether we’re talking about specific tissues, organs, proteins, or limbs, they almost always had some slightly different ancestral version that did something related.

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But what about the few cases (I’m assuming here) where it truly is a novel feature?

There are none. Zero.

Anyone who disagrees is free to provide an example.

Creationists? Nothing to say on this subject?

Relevant to this thread (open access):


Link isn’t working for me

Try this one:

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The article discusses the difference between transformations of existing structures and novelties. However, the difference appears to be a matter of degree and not a difference of kind, at least at first glance. For example,

At first, we have a transformation of the hair cells into three distinct buds, one of which is the mammary gland. This is not considered a novel feature. Later, mammary glands are able to develop on their own, separate from hair cells. It is now a novel feature. Therefore, the production of this novel feature requires the rewiring of gene regulator networks to produce an already existing feature in a new setting. Would ID/creationists agree with this distinction between transformed and novel features?


I guess we’d have to look at specific examples to assess them. I’m not agains the idea of functions evolving de novo. It all comes down to how you draw the line exactly. How should we define what counts as novel?