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How do we know we are all Homo Sapiens?

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Celebaelin
1370204.  Thu Dec 31, 2020 1:18 am Reply with quote

Yep - species is a functional term and if you circumvent the effects of climate, geography, topography or just plain distance you are actively changing that functionality.

In truth the concept of species is a biological staple which starts to get a bit fuzzy as you look more closely.

Consider that a systematic formula describes a common molecular form any given example of which is a material object and therefore occupies a particular energy state and position in space where it can sit twiddling its metaphorical thumbs until something exciting (and usually destructive) happens. Similarly a species name denotes a wide group of individuals of very similar form and which occupy broadly similar ecological niches until something exciting (and again usually destructive) happens.

OK so far (except for the unfortunate but inevitable exciting stuff).

When you look closely at a molecule however you find that it's not all exactly where you think it is and its boundaries are a bit fuzzy.

Some of you will be familiar with benzene which you may have been told looks like this:



but really looks more like the lower part of this



and those mathsy types in the physics department tell me it actually leaves tiny bits of itself scattered around the universe so that it is not even entirely in the general area of where you think it is; I bet they can explain it to you if you're willing to take the time.

Quote:
The quantum mechanical model of the atom

Introduction to the quantum mechanical model of the atom: Thinking about electrons as probabilistic matter waves using the de Broglie wavelength, the Schrödinger equation, and the Heisenberg uncertainty principle. Electron spin and the Stern-Gerlach experiment.

https://www.khanacademy.org/science/physics/quantum-physics/quantum-numbers-and-orbitals/a/the-quantum-mechanical-model-of-the-atom

Well now; moving swiftly on in the direction something resembling my point - species are a bit like that. Gross similarities in form and function allow for external generalisation about the group and internally allow the formation of a breeding community large enough that it won't randomly cease to exist because of one of those tragic but inevitable 'exciting things' mentioned earlier. In many cases the theoretical breeding population is larger than the actual one in that some form of functional barrier prevents interaction between individuals that could otherwise get it on together and play their part in preventing the extinction of the larger group.

This is the juncture where cladogenesis a.k.a. speciation strides boldly into the conversation and starts wittering on about lions, tigers and portmanteau words but fear not that is largely a distraction.

Wrenching ourselves back from that intermediate example of 'evolution in action' to focus on the functional reproductive group we get somewhat point adjacent by noticing the differences between the individuals in a breeding community. This constitutes the under publicised phenomenon of variation which is the functional agent of evolution - one creature has longer legs, another stores fat more readily and a third does all the altruistic behavioural warning call stuff and gets shat on closely followed by the obliteration of the whole group by predators against whom they have no warning system.

Diversity in form, function or behaviour is the manifestation of a less obvious change - it is the result of variation at a molecular level affecting the DNA sequences that are responsible for the more readily observable differences. Certain sequences are invariant as they are essential for a viable organism but others may be mutable or can be dispensed with altogether. As an example Vitamin C is not a Vitamin for most mammals but somewhere along the line humans dispensed with the need to be able to make it within their own bodies. An assortment of genotypes exist at any one time even within a stable breeding population and should circumstances change a selection pressure will to some extent act upon the variant forms generated by the differences in their genetic code allowing those more fitted to the new environment to gain a relative reproductive advantage. The genetic identity of a species will change from reproductive cycle to reproductive cycle even if the result is fluctuation around a steady balanced average composition best suited to the range of conditions encountered from season on season.

And there may still be that vole population on the other side of the world that could mate with the voles on the stretch of river you're looking at. That's just voles doing vole stuff, getting on with other voles when they need to and choosing vole-oriented modes of behaviour. Not like those weirdo tree voles... clade splitting bastards!

The Genetics of Vitamin C Loss in Vertebrates
Guy Drouin,* Jean-Rémi Godin, and Benoît Pagé
Curr Genomics. 2011 Aug; 12(5): 371–378

 
PDR
1370212.  Thu Dec 31, 2020 3:56 am Reply with quote

suze wrote:
I suspect you're right bob, but I didn't want to piss the Proper Scientists - people like Celebaelin and PDR - off too much.


On a point of order - I make no claim to being a Proper Scientist - only a Proper Engineer. I defer to Cel and DrBob on matters of Proper Science.

PDR

 
PDR
1370213.  Thu Dec 31, 2020 3:59 am Reply with quote

Celebaelin wrote:

And there may still be that vole population on the other side of the world that could mate with the voles on the stretch of river you're looking at. That's just voles doing vole stuff, getting on with other voles when they need to and choosing vole-oriented modes of behaviour. Not like those weirdo tree voles... clade splitting bastards!


What about Biros?

PDR

 
PDR
1370214.  Thu Dec 31, 2020 4:16 am Reply with quote

suze wrote:
This was a controversial hypothesis until only a decade ago, but by now it is generally accepted that Homo sapiens did interbreed with H neanderthalensis. Does this mean that the two ought to be classified as streams within one species rather than as separate species?


I had this very discussion once with an evolutionary biology postgrad, although my memory of the discussion is somewhat hazy because (a) it was at a party and it may have been slightly under the affluence of incohol at the time, and (b) she was rather cute any my primary objective was to steer the conversation more towards whether engineers and evolutionary biologists should attempt interbreeding*, but I digress. Her expressed view was that while H sapiens and H neanderthalensis were originally separate species they evolved into forms which could interbreed and as such converged into a a single species.

I may have remembered this incorrectly, and/or she may have been expressing a view which has since been disproven, so I'll happily defer to Cel if it's bollox. I'm sure I read somewhere that the current view is that today's human species is far more H neanderthalensis than H sapiens anyway, but again that could be something I misheard.

PDR

* sadly this question remained only theoretical because she fell under the influence of a music undergrad - such is the burden of the engineer

 
Celebaelin
1370221.  Thu Dec 31, 2020 5:55 am Reply with quote

PDR wrote:
...whether engineers and evolutionary biologists should attempt interbreeding...

I suspect the evolutionary biologist was way ahead of you there Pete - telling you the time honoured story of patient devotion and mixed gene pools tomorrow.



Rather an old image but every single tree I've seen looks like this or a more complicated version of it.

PDR wrote:
What about Biros?

When oh when will it again be safe to use the word 'oriented'?

Quote:
Somewhere in the cosmos, he said, along with all the planets inhabited by humanoids, reptiloids, fishoids, walking treeoids and superintelligent shades of the color blue, there was also a planet entirely given over to ballpoint life forms. And it was to this planet that unattended ballpoints would make their way, slipping away quietly through wormholes in space to a world where they knew they could enjoy a uniquely ballpointoid lifestyle, responding to highly ballpoint-oriented stimuli, and generally leading the ballpoint equivalent of the good life.

And as theories go this was all very fine and pleasant until Veet Voojagig suddenly claimed to have found this planet, and to have worked there for a while driving a limousine for a family of cheap green retractables, whereupon he was taken away, locked up, wrote a book and was finally sent into tax exile, which is the usual fate reserved for those who are determined to make fools of themselves in public.

Douglas Adams

 
CB27
1370263.  Thu Dec 31, 2020 1:47 pm Reply with quote

Going back to the question of whether we can trust we are all Homo Sapiens based on a limited number of DNA tests, this is ignoring a number of other facts.

1. We may have lots of gaps in our genealogical data in the past, but certainly in the past century or so there are plenty of records from around the world to show some level of ancestry for us to be certain of shared ancestry between people people who have been tested, and many of those who have not. I don't know the number this would involve, but if 0.37% of the world population have had a DNA test, I would suggest shared ancestry would make a certainty for a far larger number.

2. Diseases and viruses. We have many accounts in the past of diseases that have ravaged communities when they were introduced by other communities of humans. Even the spread of the current Covid19 virus has been able to spread to different communities across the world. Of course, there are some viruses that can be transmitted from one species to another, but if I understand the virus usually has to mutate to spread across a new species.

3. Medicines. To combat some illnesses, specific medicines and treatments have had to be developed, often using DNA and cell research. The effectiveness of these treatments across the general populace also lends support that we are all the same species.

 
Celebaelin
1370284.  Fri Jan 01, 2021 12:55 am Reply with quote

I'm hesitant about point 3 because of the effects of pharmaceuticals and other drugs across a very broad range of species. Where the level of function is fundamental the effect will be widely experienced cross-species although the question of de-toxification of the drug remains. Erythromycin can be used for the treatment of cats and dogs for instance - and very likely a great many other species.

On the other hand you could broaden point 1 quite a lot since interbreeding between ethnic groups worldwide has not been found to be problematic as a rule* and you could extend that to include family members as part of the 'verified as Homo sapiens' grouping. I'm in a bit of a quandary about where the start point of 'definitely Homo sapiens' is however.

Somebody Moroccan perhaps.

* by which I mean other than under abnormal circumstances

 
CB27
1370463.  Sun Jan 03, 2021 2:56 pm Reply with quote

I get what you say about point 3, a lot of medicine has similar effects across a range of species, but I would argue the expected standard doses, reactions and side effects may vary between species.

I think I would look more closely at the use of HeLa and other cells in certain treatments, allowing for research into medicines that have been used on people across the globe.

That find in Morocco is interesting, and may change our understanding of our own ancestry and throw up a few more questions, and it's simply because we don't have enough information to work with to make definitive pronouncements, as we might with our ancestry from 100 years ago.

However, going back to the original post, while our understanding may change a little with more finds, the fundamental question of our shared origin and that we are all the same species* hasn't changed.

* As discussed previously, there are questions as to what level you count a separate species and subspecies, but the general accepted theory is we're all Homo Sapiens.

 
pstotto
1370573.  Mon Jan 04, 2021 2:06 pm Reply with quote

CB 27 I like your point no.1. and agree with it, but it still doesn't account for all 7 billion people.

Regarding point 2, does this rule out inter-race germ warfare among humans i.e. could one develop a disease just to knock out the Chinese, for example? ( After all, they've just ruined the winter festive season and the coming ski season).

 
pstotto
1370576.  Mon Jan 04, 2021 2:10 pm Reply with quote

... And before the usual suspects have a go at me, I didn't say they were better or worse than the English apart from football etc.

 
RLDavies
1370679.  Tue Jan 05, 2021 9:56 am Reply with quote

"Species" is one of those terms that gets less and less clear the more you look into it. At a basic level it's easy -- we can see dogs are different from cats, and roses from oak trees. But when you start trying to pin down a scientific definition... well, like most things in biology it gets all complicated and squirmy and starts to be more like a rule of thumb instead of a physical law.

The usual textbook definition is a population of individuals that are all capable of interbreeding with each other, but not from individuals outside that population. On the other hand, we know that individuals from clearly separate species can interbreed at least occasionally, with human intervention and in the wild.

In practice, species are usually recognised by physical characteristics. Even with modern DNA analysis, the suspicion of "this might be something new" normally arises with realisation of a physical difference. With extinct species, all we have is physical characteristics from fossils, and eternal arguments between palaeontologists.

There have been quite a few species in the genus Homo, and most of the time two or more species have been around in the same time and place. The fossil record is patchy, but it looks like Homo is a genus (like Canis) where all the species were pretty closely related, and have all been willing and able to crossbreed with each other. Which means the human lineage isn't a nice clear-cut tree, but more like a fuzzy interwoven network.

The European branch of H sapiens has certainly done a lot of crossing with H neanderthalensis. But there's no question that all living humans are all members of a single species. We all have the same physical characteristics, with a few minor racial variations, and individuals even from opposite ends of the Earth can freely interbreed. It's unusual, having only one extant species of a genus, but there you are. It's not utterly impossible that we may yet turn up a small pocket of H heidelbergensis living on some remote island, but it's not likely.

A more interesting question to me is how the history of science and culture might have been different if there had been two or more human species living into modern times. Quite a lot of this "humans are the pinnacle of creation, set apart from nature" stuff might well have arisen because we're a single species with nothing similar for comparison.

 
Brock
1370682.  Tue Jan 05, 2021 10:08 am Reply with quote

RLDavies wrote:

A more interesting question to me is how the history of science and culture might have been different if there had been two or more human species living into modern times.


If the behaviour of Homo sapiens is anything to go by, one of the species would have asserted superiority over the other(s) and attempted to control it/them.

 
PDR
1370686.  Tue Jan 05, 2021 10:25 am Reply with quote

pstotto wrote:
CB 27 I like your point no.1. and agree with it, but it still doesn't account for all 7 billion people.

Regarding point 2, does this rule out inter-race germ warfare among humans i.e. could one develop a disease just to knock out the Chinese, for example? ( After all, they've just ruined the winter festive season and the coming ski season).


This idea was explored by John W Campbell in an unpublished sci-fi short story called "All" in the 1940s, and then used as basis of the sci-fi novel "Sixth Column" by Robert Heinlein published in 1949. Heinlein said he had to "re-slant the story to remove the racist elements" (if you read the book the idea that this is the de-racistised version may come as a bit of a surprise) and to correct its severe right-wing leanings. Those familiar with Heinlein's work would be bemused that something could be too right wing for him. But then Campbell was an overt supporter of segregation and apartheid policies, so perhaps he managed to exceed even Heinlein's right-wing limits.

PDR

 
CB27
1370706.  Tue Jan 05, 2021 11:55 am Reply with quote

There's no question that diseases can be targeted against specific races, and I know this because of an eye condition I developed some years back which mostly affects certain Jewish men in their 20s.

But this is because of the effects of a narrow spread of genes in my ancestry because for centuries many Jewish people would only marry within their faith (and because of how spread out they were, often within the same community).

As we pass on our genes, with each birth we introduce minor mutations which may or may not be passed on if we continue to reproduce. Sometimes a certain set of mutations might lead to a higher chance of survival, and therefore the ability to breed. In Europe, as we dealt with certain common diseases for several generations, those who survived and managed to breed passed on changes in their genes that gave them a better chance to survive.

In other parts of the world, such as the Americas, they hadn't encountered these diseases for several thousand years, so perhaps didn't retain or develop the needed changes to their genes through most of the population, and this is why when Europeans arrived so many indigenous people died from common illnesses.

By most interpretations we would all still be the same species because we share the same basic DNA and basic genetics, and can easily breed. However, by virtue of certain genetic markers shared by a population which is isolated from another for many generations, we would be seen as different races.

 
Jenny
1370711.  Tue Jan 05, 2021 12:10 pm Reply with quote

You know, there was some complaint about pstotto at the beginning of this thread, but it has turned out to be a remarkably interesting discussion.

The issues that CB discusses in the above post also apply in some Pakistani communities in the UK, where first cousin marriage is very common.

 

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