Greetings, all. I discovered this forum through a google advertisement on
www.iidb.org, where I am administrator and moderator of our own EvC forum. I happen to be particularly interested in this debate topic, so I hope no-one will mind if I crash in here with a few half-baked thoughts.
Unfortunately, it’s not possible to meaningfully debate this topic as stated, because of the truly extreme variation in the definitions of the term macroevolution. Definitions of macroevolution are extremely diverse. I’ve obtained this list of definitions from a poster I know from IIDB, who happens to be a PhD in evolutionary theory:
Human biology text books.
Human Biology, Fifth Edition by Starr and McMillan:
macroevolution The large-scale patterns, trends, and rates of change among groups of species.
Human Biology, Second Edition by Johnson:
macroevolution Refers to large-scale evolutionary trends or changes that apply to whole groups of species, often as a result of changing environments or major historical events.
Human Biology, Seventh Edition by Mader: no definition.
Introductory biology texts.
Biology, Sixth Edition by Campbell and Reece:
macroevolution Evolutionary change on a grand scale, encompassing the origin of new taxonomic groups, evolutionary trends, adaptive radiation, and mass extinction.
Biology, Seventh Edition by Raven et al:
macroevolution (Gr. makros, large, + L. evolvere, to unfold) The creation of new species and the extinction of old ones.
Life: The Science of Biology, Sixth Edition by Purves et al:
macroevolution Evolutionary changes occurring over long time spans and usually involving changes in many traits.
Evolutionary biology texts.
Evolutionary Biology, Third Edition by Futuyma:
macroevolution A vague term for the evolution of great phenotypic changes, usually great enough to allocate the changed lineage and its descendants to a distinct genus or higher taxon.
Evolutionary Analysis, Second Edition by Freeman and Herron:
macroevolution Large evolutionary change, usually in morphology; typically refers to the evolution of differences among populations that would warrant their placement in different genera or higher-level taxa.
Evolution by Ridley:
macroevolution Evolution on the grand scale: the term refers to events above the species level; the origin of a new higher group, such as the vertebrates, would be an example of a macroevolutionary event.
This is my favourite, from Biology, Sixth Edition by Campbell and Reece:
macroevolution: Evolutionary change on a grand scale, encompassing the origin of new taxonomic groups, evolutionary trends, adaptive radiation, and mass extinction.
It's best to think about that as a non-exhaustive list of macroevolutionary phenomena, because this definition should properly include the complete gamut of major phenomena that affect the pattern of evolutionary progression. It's thus a broad, catch-all definition that attempts to pre-emptively cover anything that any biologist might be talking about when they use this term.
So, I'll now list a few things that are often described as macroevolutionary phenomena, that can NOT be properly explained with only microevolution, where microevolution is basically anything that deals with allele frequencies. This is a combination of things listed in Cambell and Reece's biology text, and Mayrs What Evolution Is.
Rates of change: Whenever you hear about the fits and starts in the fossil record, or whenever you hear about Gould and punk eek and so on, you're dealing with a macroevolutionary phenomena that requires the consideration of geology, paleontology and ecology over and above an understanding of microevolutionary allelic shifts.
Speciation: any discussion of speciation is about macroevolution. You can't get to speciation by thinking only about alleles. Allopatric speciation considers geological barriers, and even plate tectonics (i.e. describing why a pattern of species relationships exist between certain continents could involve saying "allopatric speciations occurred in suchandsuch a period when this certain continental division happened"). Furthermore, some evolutionary phenomena like adaptive radiation are inherantly linked to the local geology.
Ecology: investigating the evolution of organisms will inevitably require investigating their ecology: competition, parasitism, just about all ecological phenomena are going to influence the direction of a species' evolution, and none of them are classifyable as microevolutionary.
Extinction: Gould has made the famous point that the investigation of evolutionary history raises questions that can only be answered by an understanding of extinction. The rise of mammals is linked to the mass extinction of the reptiles. Explaining a species evolutionary success can not be done with only microevolutionary explainations. The complex, multidisciplinarian explanations that emerge involve macroevolution, being basically everything that microevolution isn't.
These are just some of the obvious ones. Mayr has a long chapter devoted to these and many many more evolutionary phenomena that he sees as seperate from microevolution. For example, he calls convergent evolution macroevolutionary, because while it does have to to with adaptation and selection and allele frequencies, it also involves niches, geology, and environmental influences.
A picture is emerging that sees macroevolution and microevolution sharing no borders, but desribing totally separated classes of phenomena, making the question 'when does microevolution become macroevolution' meaningless. Naturally, that is not a universal truth in this game, because someone else will come along and define it in a way that does overlap.
The things to take home from this will be that macroevolution CAN refer to genuine scientifically defined phenomena that really require a separate definition from microevolution. However, in the phenomena described above, macroevolution is NOT the standard ‘large scale change’ that debates often accept as ‘the’ definition. Instead, they are observed phenomena, patterns, and interactions that are part and parcel of everyday biology, but come under this blanket term all the time. The term, in this
very widely used sense, refers to patterns and processes that emerge when microevolution carries on for some time. It thus makes little sense, under this definition, to say that one accepts microevolution but not macroevolution.
If I may be so bold, I would suggest to those who wish to make the distinction between observed modern day ‘micro’ evolution, but reject things like an old earth, or human descent from apes, that the most meaningful and appropriate distinction would be to say “I accept that evolution can be seen happening today: natural selection operates on allele frequencies, speciation has been observed. However, I do not accept
common descent of all life”. The use of such a nebulous term as macroevolution in place of the more precise and accurate ‘common descent’ only promotes confusion.
Of course, as I’ve shown, no universally accepted definition of macroevolution can be pinned down, so making blanket statements is impossible. It’s precisely because of this that more precise terms for
exactly what is being accepted or rejected need to be used.
I hope I have not bored anyone too much.
Yours
-Timothy.
