Evolution of humans

[SusanDoris]

The (braile) book* I have started reading is, 'Origins: How The World Made Us' by Lewis Dartnell, who is a professor at Westminster University and part of his job is communicating science to a wider audience.

So far it is very interesting. I am hoping that somewhere he will explain how, since Homo sapienssapiens left Africa about 40,000 years ago and then spread throughout the world, why there is such variation in skin pigmentation, eye shape, etc that could have evolved by natural selection in such what seems like a comparatively short time; while at the same time we are all still one species, able to interbreed. I can understand (as he has already said, that homo erectus left Africa and spread very widely long before that, and that Neanderthals were settled and thriving in Europe and wider, also that for some reason when homo sapienssapiens came along they disappeared comparatively quickly, but that 40,000 years is a puzzle.

I've been trying to work out how many generations there must have been in 40,000 years. If I take 4 generations per 100 years and multiply by 10 for 1000 years, that makes400,000 generations, then by 40   to get to the 40,000 years ... well, I'm foundering because I can't really do that on a piece of paper!!
I wonder if any  of that makes any sense and if anyone has any thoughts on this as I would be most interested to hear.

*The NLB have changed braille books. Instead of making this book into 7 volumes with a spiral at the centre, and each volume in its plastic, hard folder, they have a new machine which prints a book as requested (and if available of coursse) into double the number of books, stapled non-returnable and re-cyclable.

[Harrowby Hall]

I recall reading somewhere that it would take 40 generations of selective breeding to turn a wolf into a chihuahua. (And it's quite possible that my recollection is not accurate.) For natural selection to achieve the same result would certainly take rather longer.

I also recall reading somewhere that the European white skin/blue eyes formulation is possibly about 10,000 years old - that is 400 generations.

(This is not criticism but just an acceptance of the difficulties your visual problems cause, but you seem to have vastly over calculated the number of generations in 40,000 years - at 4 generations every century it would be 1,600 generations.)

[SusanDoris]

I recall reading somewhere that it would take 40 generations of selective breeding to turn a wolf into a chihuahua. (And it's quite possible that my recollection is not accurate.) For natural selection to achieve the same result would certainly take rather longer.

I also recall reading somewhere that the European white skin/blue eyes formulation is possibly about 10,000 years old - that is 400 generations.

(This is not criticism but just an acceptance of the difficulties your visual problems cause, but you seem to have vastly over calculated the number of generations in 40,000 years - at 4 generations every century it would be 1,600 generations.)

Thank youfor your reply- it is all very interesting.  I tried putting a question into google, but the predictive text - which I can't see of course and although this is probablyk very useful to most people, it isn't to me! - meant that it kept coming up with answers which didn't help.
this book is going to take me quite a long while to read, and, while getting used to the way an author writes, it is often necessary to read a page a couple of times. It usually gets easier as I go along. 

[SteveH]

I think your maths is a bit out: at four generations per century, there would be 1760 generations in 40,000 years.
Richard Dawkins once asked us to imagine a woman on Brighton beach, standing sideways-on to the sea, which is on her right. her left hand is holding the right hand of her mother, whose left hand is holding the right hand of her mother, and so on all the way up to the Scottish border, where the first woman's remote ancestor is holding in her left hand the right hand, not of her mother, but her sister, who is facing her, not alongside her. Her left hand is holding the right hand of her daughter, who is holding the right hand of her daughter, and so on, all the way back down to Brighton beach, where the woman we started with is face to face with a chimpanzee. (If memory serves, the illustration uses females throughout because the ancestry is traced through mitochondrial DNA, which is passed down on the female side.)

[SusanDoris]

I think your maths is a bit out: at four generations per century, there would be 1760 generations in 40,000 years.
Richard Dawkins once asked us to imagine a woman on Brighton beach, standing sideways-on to the sea, which is on her right. her left hand is holding the right hand of her mother, whose left hand is holding the right hand of her mother, and so on all the way up to the Scottish border, where the first woman's remote ancestor is holding in her left hand the right hand, not of her mother, but her sister, who is facing her, not alongside her. Her left hand is holding the right hand of her daughter, who is holding the right hand of her daughter, and so on, all the way back down to Brighton beach, where the woman we started with is face to face with a chimpanzee. (If memory serves, the illustration uses females throughout because the ancestry is traced through mitochondrial DNA, which is passed down on the female side.)

Thank you - much appreciated. I can just imagine that! However, I find it really difficult to get my head round the time scales, but hope to be better informed when I've read the book.

It seems too that the sites of major tectonic plate movements, mainy the Great Rift Valley inAfrica had a huge effect on homini* evolution.

* This is the word used as a general term it seems.

[SteveH]

My maths is out, as well. There'd be 1,600 generations in 40,000 years.

[Sriram]

Different genetic variations could have arisen due to interbreeding with other homo species such as Neanderthals and Denisovans.

[SusanDoris]

Different genetic variations could have arisen due to interbreeding with other homo species such as Neanderthals and Denisovans.

Yes, this makes sense I think.

Actually, I thought I knew quite a bit about geology, but I don't think I had realised vbefore reading the part I have read these last couple of days that ice ages came after the dinosaur age.

The fact that we, the human species, are here after the whole long run of evolution is stunningly amazing.

[Roses]

I wonder if we will continue to evolve and what the species would be like in thousands of years time assuming our planet still exists?

[torridon]

I wonder if we will continue to evolve and what the species would be like in thousands of years time assuming our planet still exists?

Sure, we are still evolving.  Currently we are evolving a new (median) artery in the arm, for instance.

https://www.sciencefocus.com/news/humans-are-evolving-an-extra-artery-in-the-arm/

[Sriram]

Yes, this makes sense I think.

Actually, I thought I knew quite a bit about geology, but I don't think I had realised vbefore reading the part I have read these last couple of days that ice ages came after the dinosaur age.

The fact that we, the human species, are here after the whole long run of evolution is stunningly amazing.

There are regular and alternating glacial (period of glacial advancement) and interglacial (period of glacial retreat) periods.  We entered an interglacial  period about 10000 years ago.

[SusanDoris]

There are regular and alternating glacial (period of glacial advancement) and interglacial (period of glacial retreat) periods.  We entered an interglacial  period about 10000 years ago.

The latest pages I read yesterday explain why the world was so hot before that and how the tectonic plate movements changed things. It is all very interesting.

[torridon]

There are regular and alternating glacial (period of glacial advancement) and interglacial (period of glacial retreat) periods.  We entered an interglacial  period about 10000 years ago.

Quite.  The Pleistocene ice age was one of the worst periods for life in Earth history with extreme volatility in the climate, record lows in CO2 levels etc and yet it was this awful period in which humans evolved.  The rather sudden onset of the Holocene ushered in a new climate, stable, warm with plentiful rainfall and higher CO2 levels making farming a viable means of making a living. Hence the exponential growth in human numbers, hence the rise in civilisations, hence the rise in energy consumption, resource depletion and ecosystems degradation all of which now threaten the benign stable conditions which allowed for our success in the first place.

[Sriram]

Quite.  The Pleistocene ice age was one of the worst periods for life in Earth history with extreme volatility in the climate, record lows in CO2 levels etc and yet it was this awful period in which humans evolved.  The rather sudden onset of the Holocene ushered in a new climate, stable, warm with plentiful rainfall and higher CO2 levels making farming a viable means of making a living. Hence the exponential growth in human numbers, hence the rise in civilisations, hence the rise in energy consumption, resource depletion and ecosystems degradation all of which now threaten the benign stable conditions which allowed for our success in the first place.

Yeah. And the glacial period allowed for many land bridges between different land masses. Bering strait, Palk strait, between Indonesian islands and so on, that allowed humans to settle around the world....from 40000 to 15000 years ago....  The warmer climate for the last 10000 years has enabled agriculture, urban settlements and civilization as we know it...

Meant to be...IMO 

[Outrider]

Sure, we are still evolving.  Currently we are evolving a new (median) artery in the arm, for instance.

https://www.sciencefocus.com/news/humans-are-evolving-an-extra-artery-in-the-arm/

Another example of ongoing evolutionary change is the trait, predominantly present in the European population, of being able to digest lactose.

https://www.npr.org/sections/thesalt/2012/12/27/168144785/an-evolutionary-whodunit-how-did-humans-develop-lactose-tolerance?t=1623222222196

O.

[SusanDoris]

The book continues to be very interesting on every page. The thing that has always puzzled me, and which I hope supplies the answer to that puzzling, is how a population of a few thousand could have multiplied so quickly  - well, comparatively quickly - and disperse throughout the world, plus becoming so different in outward appearance. One of the reason could be that if they interbred with the homo erectus (or other) hominis who had survived the Ice Age then those genes could have helped I suppose.
Edited to say: more likely Neanderthals though.

It is completely astonishing to me that there ar so many people who believe that ETs are either popping down here occasionally or actually are amongst us all the time who manipulate human genes. Why, oh why, when there is such far, far more fascinating science to learn about!

[Sriram]

Homo Erectus is way up the line.....one of the earliest of the Homo genus (emerged about 2 million years ago). It was probably the early ancestor of Homo sapiens as also Neanderthals and Denisovans.....and probably became extinct around the time Homo Sapiens were emerging.

[SusanDoris]

Homo Erectus is way up the line.....one of the earliest of the Homo genus (emerged about 2 million years ago). It was probably the early ancestor of Homo sapiens as also Neanderthals and Denisovans.....and probably became extinct around the time Homo Sapiens were emerging.

That seems to be the right chronology. Near the start of the book, the author appeared to say that adaptations or mutations could be developed rather than being random, so I sent an e-mail to ask. He has written an e-mail today, thanking me for my interest and explaining clearly what the position is

No, no organism can initiate particular mutations. All mutations are random errors that occur in the DNA, but through natural selection any mutations that act to enhance the survival or reproduction of an organism become more prevalent in the next generation – this is how over time (over many generations) organisms become better adapted to their environment.

So it is nice to have clarity.

[BeRational]

Another example of ongoing evolutionary change is the trait, predominantly present in the European population, of being able to digest lactose.

https://www.npr.org/sections/thesalt/2012/12/27/168144785/an-evolutionary-whodunit-how-did-humans-develop-lactose-tolerance?t=1623222222196

O.

What is driving this evolution do you think?

Surely, people that are lactose intolerant (in Europe)  do not die before they have children?

I am surprised that humans are evolving so much as we work to avoid this, by making sure people survive as long as possible.

[torridon]

That seems to be the right chronology. Near the start of the book, the author appeared to say that adaptations or mutations could be developed rather than being random, so I sent an e-mail to ask. He has written an e-mail today, thanking me for my interest and explaining clearly what the position isSo it is nice to have clarity.

Hey, that's nice. Write to the author and get a reply; it's not every author that would do that, well done.  Lewis Dartnell has just gone up in my opinion, not that he was low before 

[torridon]

Another example of ongoing evolutionary change is the trait, predominantly present in the European population, of being able to digest lactose.

https://www.npr.org/sections/thesalt/2012/12/27/168144785/an-evolutionary-whodunit-how-did-humans-develop-lactose-tolerance?t=1623222222196

O.

Another one is the spread of a variant of the EPAS1 gene that confers enhanced oxygen transport, just what you need if you live at high altitude. The incidence of this allele is something like 90% in the population of modern Tibetans, compare that to 10% incidence in the population of Han Chinese, from whom Tibetans derive.  This is maybe evidence of the harshest selection pressure on any population of humans in recent millennia, the mortality rate amongst the population of Han Chinese who migrated up into the Himalaya not carrying this mutation must have been awful.

https://en.wikipedia.org/wiki/EPAS1

[Outrider]

What is driving this evolution do you think?

Surely, people that are lactose intolerant (in Europe)  do not die before they have children?

Not in large quantities, I should think, but to a small degree perhaps, so it's not run wildfire through the human population but it's gradually spready.

O.

[SusanDoris]

What is driving this evolution do you think?

Surely, people that are lactose intolerant (in Europe)  do not die before they have children?

I am surprised that humans are evolving so much as we work to avoid this, by making sure people survive as long as possible.

I think the phrase 'driving evolution' is out of place. Evolution happens, it is not driven by anything. If mutations occur which happen to be beneficial and are passed on that is fortunate and happens by chance. I do not think it can be said to be 'driven' by anything.

[BeRational]

I think the phrase 'driving evolution' is out of place. Evolution happens, it is not driven by anything. If mutations occur which happen to be beneficial and are passed on that is fortunate and happens by chance. I do not think it can be said to be 'driven' by anything.

I agree to so e extent, but to be beneficial they have to be more efficient at passing on the gene. This would mean that others would not be as successful at passing on their genes.
We strive quite rightly to make sure people are not disadvantaged so I am not sure how this evolution is taking place. Unless there are losers there is nothing for evolution to grab onto. Is there?
Or am I missing it?

[Harrowby Hall]

Evolution has no purpose or goal. Mutations are random - those which are beneficial may take several generations to demonstrate their advantages. The benefit of a favourable mutation is that it may provide you with a marginal advantage over someone who does not possess it.  It is possible that everyone, following conception, may have a genome in which several unplanned, totally random, copying errors, mutations, have taken place

For the most part these mutations are of no consequence but it is possible that one may give a particular advantage if a particular environmental situation occurs.

If the environmental circumstances which make the mutation advantageous persist, then those possessing the mutation are more likely to survive and pass their mutation onto their offspring. Those not possessing it may find it difficult to cope with the environmental conditions, possibly die early and fail to reproduce successfully. If they do reproduce then their offspring will be similarly disadvantaged.

Evolution works essentially by having a small number of winners and a large number of losers but eventually the winners will outnumber the losers.

but to be beneficial they have to be more efficient at passing on the gene. This would mean that others would not be as successful at passing on their genes.

It has nothing to do with efficiency, merely - by possessing a particular mutation - being better equipped ...  fitness ... to survive. Those not so equipped are more likely not to survive.