h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

I just did a little Googling. An elephant (I'm assuming this is the largest land animal) can reach a little under 7 metric tons. The theoretical limit for a land animal is about 100 tons, with a brontosaurus at about 80 tons for comparison.

This is a pretty good indication that overall genetic diversity is currently quite low methinks.

Is there a limit to size for mammals? Are you talking about the end of times for the dinosaurs? That may have been a supervolcano as well but currently most people lean toward a massive meteor hit.

Hi Noggin,

Please note I used the word "hominids", not "humans." Homo Sapiens, as opposed to Homo Neanderthalis, begins to appear as a distinct species about 200,000 years ago, as you say. But how long did it take for H.Sapiens to evolve from whatever previous hominid form into that recognisably Sapiens type?

It's just a bit scarey to think that H.Sapiens hasn't been around longer than one third of a Yellowstone cycle ( 600,000 years + or - ).
I don't know how much DNA diversity they reckon should have arisen within one species in 200,000 or so years. In the last 75,000 years since the Toba eruption, we seen to have diversified quite bit.

This thread reminded me of an epitaph for Earth that appears in Hocus Pocus by Kurt Vonnegut,
'We could've saved it, but we were too doggone cheap'

Interests me that the Toba super volcano erupted in *Indonesia and "Mitochondrial Eve" turns up in Africa. I would have suspected that she'd have survived further away from the eruption, although I'm having trouble imaging how the earth would look after such an event. Since a yellowstone event is predicted to have a dramatic affect on the whole planet and Toba was larger I'm assuming that the further away from the site , the more chance of survival. Or doesn't it work like that? the documentary showed such a change in planet wide climate that livestock (but they wouldn't have that would they?) and crops (nor that either?) that food would have been limited. So how did these primitive peple survive I wonder and if we knew, would there be a lesson for all of us?

* And that is also the site of the latest large earthquake activity.

Hi annnew

It's the aerosol particles in the atmosphere which change the climate, and I think they only take a few months or so to permeate the atmosphere globally. After that happens it doesn't really matter where you are. After such a large eruption, anything nearby would be killed off, but it's about 4500 miles from Indonesia to East Africa, so I think most things would survive the blast easily enough.

No, I wasn't talking about the dinosaurs, Brontosaurus was just a point of comparison, as I said.

The point was that large animals get extinct easily, so a good general measure of diversity would be to look at how big the biggest animals are.

"Is there a limit to size for mammals?"

Well I would expect eventually. 100 metric tons wouldn't be nearly enough for a Blue Whale though. My point was very specifically about land animals. The theoretical size limit comes from having to support your own weight.

Hi Annew,

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My understanding is that Mitochondrial Eve is the earliest human female whose mitochondrial DNA survives in an unbroken mother-daughter chain. She dates, theoretically from long before the Toba eruption. There would have been several female carriers of her mitochondrial DNA among the Toba survivors.

Interestingly, there are now suggestions that it may be possible to trace a theoretical mitochondrial Adam through a similar father-son linkage.

Here's a googled piece on the implications of Mitochondrial Eve:
__________________________________________________________________

The Mitochondrial Eve of 200,000 years ago (ME for short henceforth) is NOT our common ancestor, or even common genetic ancestor. She is the most-recent common ancestor of all humans alive on Earth today with respect to matrilineal descent. That may seem like a mouthful, but without even a single one of those qualifying phrases, any description or discussion of the ME reduces to a lot of nonsense.
While each of us necessarily has two parents, we get our mitochondria and mitochondrial DNA from the ovum (and hence from our mothers). Our mothers got their mitochondrial DNA from their mothers and so on. Thus, while our nuclear DNA is a mish-mash of the DNA of our four grandparents, our mitochondrial DNA is an almost exact copy of the DNA of our maternal grandmother (the match may not be exact due to mutations. In fact, the mutations in the mitochondrial DNA provide the molecular clock that allows us to determine how much time has elapsed since the ME lived).
The ME represents that woman whose mitochondrial DNA (with mutations) exists in all the humans now living on Earth. That does not mean that she is our lone woman ancestor. We have ancestors who are not via matrilineal descent. For example, our father's mother (who did pass on her mitochondrial DNA to her daughters) is an example of an ancestor who is not matrilineal to us. However, she did exist at one time and was probably of the same age as our mother's mother, who is a matrilineal ancestor of ours and from whom we got our mitochondrial DNA.

The term Mitochondrial Eve itself is a title given retroactively to a woman. Often (and as is certainly the case with the ME that we are discussing) the conferring of the title occurs many hundreds of thousands of years after the death of the woman in question.

ME lived with many other humans (men and women); she was certainly not alone. When she was alive, she was most certainly NOT the Mitochondrial Eve. The title at that time was held by a distant ancestor of hers (and of the many humans who were her contemporaries).

The existence of the Mitochondrial Eve is NOT a theory; it is a mathematical fact (unless something like a multiple-origins theory of human evolution i.e. the human species arose independently in different geographically separated populations, and that the present-day ease of interbreeding is the result of a remarkable convergent evolution, is true. Few people subscribe to the multiple-origins theory, and the Mitochondrial Eve observation is a refutation of multiple-origins).
_________________________________________________________________

There is also a short piece about "Mitochondrial"...actually Y-chromosome... Adam

<>

Every time a woman has more than one daughter a new lineage of mitochondrial DNA is created. The "age of separation" of these lineages cn be gauged by the difference between them. The "genetic bottleneck" in mitochondrial DNA basically boils down to there being very few of these lineages whose separation points go back beyond 75,000 years - a lot fewer than one would expect given the estimated age of Mitochondrial Eve herself.

Noggin

This topic (limits to size for mammals) was discussed in the book 'The Science of Middle Earth' by Henry Gee which I have just finished reading. It's a great book!

Meanwhile, for those who have BBC, it's off to the telly to see what's going to happen if and when the Gulf Stream ceases to operate...a programme called "The Frozen North" due to start in about half an hour from now ( 10.00pm GB/Irish time ).

C U later folks...it's bound to add an interesting new element of panic to our discussions here.

C \|/

A project spanning five continents is aiming to map the history of human migration via DNA.

These and other unanswered questions form the research goals of the project. They include:


Who are the oldest populations in Africa - and therefore the world?
Did Alexander the Great's armies leave a genetic trail?
Who were the first people to colonise India?
How has colonialism affected genetic patterns in Africa?
Was there any admixture with Homo erectus as modern humans spread throughout Southeast Asia?
Is there any relationship between Australian Aboriginal genetic patterns and their oral histories?
What are the origins of differences between human groups?
Is it possible to obtain intact DNA from the remains of Homo erectus and other extinct hominids?


http://news.bbc.co.uk/1/hi/sci/tech/4435009.stm

Wow, I hope we get the information here in New Zealand!

Taking my prompt from this thread, I've just finished updating my original Edited Guide Entry "Extinction Level Events". It's in the Update Forum - entry A3785123. Any comments will be most welcome.

Checking it out, Woodpigeon...

This is a report primarily about the hobbits.
But Adelaide brought up the animal sizes and it also ties in a nit with other comments. You can watch the video or read the article.

Animals changed in size to fit their needs, maybe people did too. Makes you wonder if there were giants around when the large dianasours were here.

http://www.cbsnews.com/stories/2005/04/28/60minutes/main691775.shtml
It is also available on the National Geo site.

The Hobbit’s brain was a third the size of one of ours. And scientists had always used brain size as the most important characteristic separating humans from other animals -- that and the ability to use tools and build fires.

(Building fires was left out of the what makes us human thread. I had never considered that uniquely human but it is)

"The Hobbits may no longer be with us, but the animals they hunted are still here. Komodo dragons are alive and well and hanging out not far from where the young lady skeleton was found. In fact, dragon bones from the same period have been discovered in the Hobbit’s immediate proximity.

"How do you think that the Hobbits actually went about getting the dragons?" Simon asks Professor Mike Morwood.

"You walk up to them in the morning when they’re still cold before they’ve warmed up, and you bang them on the head, OK? You wouldn’t want to try it when the sun’s up and they’re warmed up," says Morwood.

Morwood will tell you that when the Komodo dragon arrived on this island, he wasn’t nearly as large and lethal as he is now. He was just a small reptile. That happens on islands over the millennia.

Small animals get bigger so they can survive better. And big animals get smaller so they can live on less food. Eventually, they evolve into new species. Hence the miniature elephant, the Stegadon, and now the Hobbit.

Little animals. Little people. Ms. Hobbit lived here, eating her dragons and elephants 18,000 years ago.

I was reading that scientists are very surprised that the "Hobbits'" brain capacity is so small, but the striations on the skull show that it was intelligent... I heard on the world service, an interview with a man who claimed his grandparents had met them! (In other words, they were around alive and kicking, within the last century!)

<> abbi

Does that mean you think other species of Homo are human, like the Neanderthals, Homo Erectus (and Floresiensis) and the various pre-Neanderthals which were around about 500,000 years ago?

If they were still around today, they may well be considered human by more or less people depending on their appearance, behaviour and apparent intelligence.
Even if not considered exactly like us, their existence might well cause a serious redefinition of categories, with a part-human category making more sense than it does at present.

Even though much is made of brain size when assesing intelligence, I'm not sure how good a guide it really is. In modern humans there's something like a 2:1 variation between the largest and smallest normal adult brains, with no huge correlation with intelligence as far as I am aware.

I understand it is the case that larger animals tend to have physically larger neurons, so neuron count (or brain complexity) doesn't necessarily scale directly with brain weight. With homo floriensis, that might be a factor worth bearing in mind.