What do you call small changes to a species?

[^^^Jimbo^^^]

My friend and I were having a debate the other day about Aborigines and other different indigenous peoples. He was commenting on the way that Aborigines have failed to integrate into modern society, and thought maybe it was evolutionary. Because they left Africa so many thousands of years ago, he thinks they may have 'evolved' slower, or not at all and that they are unable to learn white culture. I disagreed and said that I thought it was a cultural thing. They have been hunter-gatherers for so long that their culture of learning is different, and perhaps they prefer to continue the lifestyle they have lived for millenia. You don't expect all of the tribes in Africa to suddenly move to the cities and adopt white lifestyles, so why Aborigines? Or the Laps who live with the great Reindeer herds in and around Finland, and follow them in their yearly migratory movements? Or the nomadic Bedouin? But we both wondered about small, localised changes in humans physically, what you define them as. Such as skin colour, which is just selected for depending on how many hours of sunlight per year and how strong it is etc where that particular cultural group lives. Or the high cheekbones of Native americans and their lack of body hair. Because humans are 99.99% the same, what do you call these little changes? I though evolution was natural selection of mutations that led to a different species, or different branch of a species altogether. Humans are all the same species with small localised differences, so surely this is not full on evolution, but maybe micro-evolution?
I hope I have made the point and raised the question in such a way that no one is offended and someone has an answer. Thankyou.

[Jose]

Welcome to the fray, Jimbo!

Actually, microevolution is evolution. That's how it works. The problem with talking about "big" changes vs "small" changes is that "big" and "small" don't actually make sense. All changes result from changes in DNA sequence...the only difference is in which genes happen to undergo changes. It could be the same change--a C replacing an A, for example--and have a minor effect in one gene, no effect in another, and yet cause a dramatic change in appearance when the DNA change occurs in a different gene.

So, I have clearly not answered your question. You're welcome. Glad to help.

[micatala]

Hi Jimbo, and welcome to the forum.

First, I would agree that the differences in the aboriginal and white societies you are describing are cultural. These differences could certainly occure between populations which were genetically more similar than these two.

I don't make a distinction between micro-evolution and macro. It is really the same process, just a difference of degree. Yes, we have not observed modern humans splitting into different species, and this is not likely to happen given the global nature of our population and mobility.

Yes, we do have 'localised differences' between populations, and yes I think it is fair to say that some of this is due to environmental selection pressures (e.g. hot sunny weather selects for dark skin).

As long as the populations are capable of interbreeding, we will think of them as one species. Within localized groups, we may see changes (evolution) occurring which results in a different spectrum of variability with regards to different characteristics. If the populations attain a large enough difference in enough characterics, they may no longer be capable of inter-breeding, and so might become different species. Again, this has not happened in recent times with people, but certainly has happened with respect to other species.

[^^^Jimbo^^^]

Okay, so the barrier between different species is the ability to interbreed? That makes sense. And micro-evolution being evolution still makes sense. I read a thing about the birds on the Galapagos islands, how over different years the average beak size changed quite dramatically depending on the availability of certain types of grain/nuts. That was micro-evolution, so I guess that skull shape and average height etc in humans would be a similar thing. Thanks for the explanations.
As for the cultural thing, do you agree that if you took a newborn baby from any culture, even a tribe living in a south american jungle, and raised it in a completely different environment, like a modern farm for instance, that the child would grow up to be the same as those who raised it? My friend says maybe, I say most likely, but can you really say that everything we do is impressed upon us by our immediate environment?

[micatala]

Good question. Which is more important 'nature' or 'nurture?'

My own view is that the nurturing would have by far the greatest effect, but that it is likely the 'nature' would also have some effect. It can be hard sometimes to separate the effects of each.

[Grumpy]

Jimbo

Okay, so the barrier between different species is the ability to interbreed?

Not only the ABILITY but also the LIKELYHOOD of interbreeding. If one type of deer developes unique headdress(horns) and the females will only choose those males with that specific set of antlers then even if it would be productive(of offspring) the species would not interbreed with others. Then, as the two(or more) different kinds of deer experienced their own mutations, they would grow further apart over time. The seperation of breeding stocks(for the above reasons or by geographical seperation) is the first step toward speciation.

Horses and Donkeys, Lions and Tigers, even Orcas and Dolphins can produce offspring but would not willingly do so in nature and the offspring are often sterile. These species are in the process of diverging.

Grumpy 8)

[Jose]

Okay, so the barrier between different species is the ability to interbreed?

It's the most common definition--referred to as the "biological species concept." As you say, it makes sense. BUT, for unicellular, asexual things like bacteria, that don't mate, it doesn't work. There, species are defined more on the basis of biochemical characteristics and (if visible) morphological characteristics.

As for the cultural thing, do you agree that if you took a newborn baby from any culture, even a tribe living in a south american jungle, and raised it in a completely different environment, like a modern farm for instance, that the child would grow up to be the same as those who raised it? My friend says maybe, I say most likely, but can you really say that everything we do is impressed upon us by our immediate environment?

The latest data from studies of identical twins separated at birth, and raised in different environments indicates that about 80% of behavior is genetically-determined. Frankly, I'm not sure how you quantitate behavior (what does 80% mean?). But, what is considered "genetically-determined" is the broad characterization of behaviors, like "being introverted" or "being social" or "responding to challenges belligerently." It's not "you will do this!" Certainly culture has a lot to do with what people actually do, because it presents us with different stimuli to respond to. So, even if a characteristic type of response is genetic, culture will shape the way it plays out in real life. Does that kind of make sense? I'm not convinced I've said it well...

[^^^Jimbo^^^]

You've said it well enough for me. Thanks for all of that, guys:)