I strongly recommend Larry Moran’s analysis of the paper on mammalian macroevolution that I briefly described earlier today.
Just curious — how does macroevolution happen when there’s no such thing as a random mutation that adds a new, novel body part? And since organisms are individually adaptive to the environment(environmentally-induced gene expression, horizontal gene transfer, phenotypic plasticity, etc ) what is the point of natural selection adapting them?
Bennet, generally speaking macro-evolution is seen as the end result of a long series of microevolutionary changes within a group of organisms. These result in the separation of the original group into subgroups that cannot interbreed if given the opportunity. That said, I find it an incomplete explanation. I think there are certain mutations with rapid macroevolutionary rather than microevolutionary potential, a prime example being the chromosome 2 fusion event that most likely finally separated the homonid from the chimpanzee line.
Since this post is about mammalian evolution I think you should try to define which novel body part has suddenly appeared – most biologists, notwithstanding Goulds punctuated equilibrium ideas, tend to see all mammalian body plans being the result of the gradual modification of the original ancestral mammalian structures.
As for natural selection and the environment, environmental changes are very important considerations. Most of Europe and North America was covered in ice and populated by mammoths, wooly rhinos and reindeers, not that long ago during the recent ice ages. The American continent has almost doubled in area in the past couple of million years due to tectonic plate movement allowing bridging between North and South. All of these events have real consequences for the likelihood of organisms to survive or even spread and flourish in new geographic areas and as such increases the pressure for them to constantly adapt.
both of you are so far off of what is meant by macroevolution wrt the subject of this paper it’s scary.
do read larry’s analysis to find out how the term is actually used, rather than make the assumption that it means anything related to change within an organism.
It’s debatable in my mind as to whether the term actually has broad functional value, but the paleos seem to use it to good end, so it’s no skin off my nose.
as a biologist who studies evolution within populations in the field, it’s simply not applicable.
What “new body parts” do you believe must have been added?
Be careful about the examples you select, because there are remarkably many features that can be shown to be modifications of existing features.
The wings of flying animals do not pop out of nowhere, in the fashion of pegasus and angel wings, but are modifications of existing body parts. Bird, bat, and pterosaur wings are very clearly modified front limba, and insect wings are gills.
The limbs of land vertebrates are modified side fins; one can even follow the transformation in the fossil record with such fossils as Tiktaalik.
Flower parts — sepals, petals, stamens, and carpels — are modified leaves.
Etc. etc. etc. — this is rather elementary evolutionary biology.
Frankly, I don’t recommend it. Never accept molecular divergence date estimates at face value, always study the method and the calibration points…
bennet, what is your definition of “macroevolution”? There are lots of definitions out there, and under some of them there may not be any macroevolution in the whole mammal tree, whereas under another the origin of every species is called macroevolution. Like MartinC I find the term rather useless.
most biologists, notwithstanding Goulds punctuated equilibrium ideas, tend to see all mammalian body plans being the result of the gradual modification of the original ancestral mammalian structures.
The punctuations only appear if you look very closely, at quite small timescales (and even then not always). From a bit farther away it’s all as gradual as ever.
Re: novel mamalian structures, the sonar-related stuff on toothed whales is pretty interesting. “At the Water’s Edge” had some interesting bits on that. Does anyone here know what the latest consensus is?
Also, what about horns / antlers? What tissues / structures are they derived from? They aren’t homologous, right? Is there (was there) any animal with both?
Also, what about horns / antlers? What tissues / structures are they derived from?
Outgrowths of the frontal bones.
They aren’t homologous, right?
AFAIK they are (remember giraffe horns), but that’s not my specialty.
Is there (was there) any animal with both?
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