SciBlogs

Posts Tagged human evolution

human facial features the result of being used as a punching bag? somehow I don’t think so Alison Campbell Jun 11

No Comments

I saw this story in the newspaper yesterday, & again today on one of the science feeds

Researchers in the US have studied the skulls of ancient human ancestors and concluded that fist-fighting may have played a role in shaping the male face.

You can read the paper itself here (Carrier & Morgan, 2014). I'm sorry, but to me it reads like a just-so story. Just because modern humans take a swing at each other from time to time, doesn't mean that this was the case for earlier hominins. The authors of the paper argue that the facial features of robust australopithecines are the result of natural selection acting through bare-fist fighting. However, they don't offer any actual evidence that this might have happened: nothing on whether paranthropine skulls show the sort of facial damage that you might expect if fighting in this way was sufficiently widespread to act as a selective force. And similarly, no real discussion of whether Paranthropus could form a fist capable of doing such damage. (The paper on Australopithecus sediba to which they refer actually describes sediba's hand as a mosaic of features.) In other words, they're making a sweeping assumption – that paranthropines routinely beat the heck out of each other – to support the a priori assumption that our own facial evolution was shaped by this.

There's also the question of whether modern human faces show much evidence of having evolved in this way; they actually seem quite prone to damage. Noses & cheekbones are rather susceptible to damage, and the bones of the cranium – thinner than those of Paranthropus - are dangerously easy to break. At the same time, according to the authors' speculative view, our hands are particularly well adapted to deliver blunt-force trauma.

This quote from the paper (emphasis mine) says it for me; we really are dealing with conjecture & imagination: 

Starting with the hand of an arboreal great ape ancestor, it is possible to imagine a number of evolutionary transformations that would have resulted in a club-like structure adapted for fighting.

Rudyard Kipling might have appreciated it – a point also made by Brian Switek in his excellent commentary over at National Geographic.

Carrier, D. & Morgan, M. (2014) Protective buttressing of the hominin face. Biological Reviews doi: 10/1111/brv.12112

 

the daily mail comes late to the pig-ape hybridisation idea Alison Campbell Dec 02

No Comments

In posting an item about the ‘pig-ape hybridisation’ suggestion for human origins, the Daily Mail is a) coming rather late to the story (a slow day in the newsroom, perhaps?) and b) showing more regard for sensationalism than for good investigative journalism.

The story’s one I’ve posted about before (& I’ve reposted my original piece below). Seeing it again really makes me think that the originator of this particular idea is trying to have it both ways. If our morphology is as similar as he claims to that of pigs, and different from chimps, then the differences should show up in our genes. Yet they don’t; genetically we are much closer to chimps than to swine. He claims that this can be explained by repeated back-crossing with early humans – which is effectively no more than special pleading (& conveniently ignores the issue of significant differences in chromosome number between the two taxa). 

 

The internet is a wondrous place: a source of information, of amusement, and – alarmingly often – of material that elicits a combination of ‘say what?’ and <head-desk>. And a hat-tip to PZ Myers for this particular example…

For it has been proposed (by the originator of this particular hypothesis, & further discussed on phys.org) that humans arose as the result of an interspecies hybridisation event, rather than the current model for human evolution that sees chimps and humans sharing a Last Common Ancestor 5-6 million years ago and following their own trajectories since that time.

The event? Hybridisation between great ape (specifically, chimpanzee) & wild boar.

?

?

?

Now, we know that hybridisation happens; that the ‘biological species concept’ is not an absolute. But these events are generally between reasonably-closely related species: hybridisation is quite common in the waterfowl, for example. But even in birds, where hybridisation is well-documented, it doesn’t appear to cross the lines between one taxonomic order and another. Yet the ‘pig+ape’ suggestion requires hybridisation between different taxonomic orders – orders that (so fossil & genetic evidence tell us) have been separate for between 79 & 87 million years.

Surprisingly, Dr McCarthy, a geneticist and the proponent of this novel hypothesis, doesn’t present much in the way of genetic data to support it. He does agree that, genetically, we are closer to chimpanzees than to any other mammal, but suggests that this is due to back-crossing (with the chimp parent) after the initial hybridisation event:

And why might one suppose that humans are backcross hybrids of the sort just described? Well, the most obvious reason is that humans are highly similar to chimpanzees at the genetic level, closer than they are to any other animal. If we were descended from F1 hybrids without any backcrossing we would be about halfway, genetically speaking, between chimpanzees and whatever organism was the other parent. But we’re not. Genetically, we’re close to chimpanzees, and yet we have many physical traits that distinguish us from chimpanzees.

Surely the simpler explanation – that we are genetically similar to chimps because we are sister species – is more likely. Especially since at least some of the differences between the two species can be explained by differences in timing of developmental stages (the relative proportions of face & skull, for example), which may be sheeted home to mutations in regulatory portions of the genome.

In addition, there are major differences both in chromosome number (38 in pigs, 46 in humans) and in the position of various genes on those chromosomes that would make successful gamete production in any hybrid unlikely in the extreme (always supposing the hybrid was actually viable) - PZ discusses this in more length.

But anyway, what about those physical traits that “distinguish us from chimpanzees” & supposedly reflect our shared heritage with pigs? There’s a long list here. Many of them relate to bipedalism; to me, it’s special pleading to suggest that (for example) the presence of large gluteal muscles in bipedal humans and in domestic pigs is evidence of a close evolutionary relationship (Animal Farm aside, there is a distinct lack of evidence for bipedal locomotion in suids – and strong evidence of selective breeding for large backsides in pigs destined to become bacon & pork). Hairlessness? Only in domestic pigs; anyone who’s watched a huntin’&fishin’ show on TV will have seen how hairy a wild boar is. Pigs & humans both have longer hind-limbs than forelimbs, & shorter digits (compared to chimps)? Well, ye-es, I guess so, but that’s hardly evidence for a close relationship; one could say the same of mice… Similarly, while humans & pigs may (usually) be particular about where they defecate, well, so are other animals; rabbits, anyone? As for “snuggling [snuggling???], tears, alcoholism “being shared features in humans & pigs but not chimps… chimps & humans both have an enzyme (alcohol dehydrogenase 4) that allows us to break down ethanol, and it seems that chimps can become addicted to alcohol if given the opportunity.

Also offered in evidence are those diseases which are rare in non-human primates: “heart attack, atherosclerosis, and cancer (melanoma)”. Since these are to some degree, age-related, their relative rarity (for they are not absent in apes) may be ascribed to differences in lifespan: chimps in the wild may not live long enough to develop them.

Annoyingly, I see that over at uncommondescent, this proposal has been presented as even more evidence that evolutionary biologists are Getting It Wrong!

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Perusing more of the macroevolution website, I found the suggestion that armadillos and pangolins evolved from ankylosaurs and stegosaurs (page 244 at that link). It would be interesting to hear a palaeontologist’s taken on that one, but the fact that dinosaurs had diapsid skulls while mammals are synapsid doesn’t help.

migration and ear wax Alison Campbell Nov 08

No Comments

Last year’s Schol Bio paper contained (as is usual) some interesting and challenging questions. One of them was about earwax. More specifically, the earwax phenotypes ‘dry’ and ‘wet’, and what their distribution can tell us about patterns of human evolution. (Note to those sitting these examinations: most questions have a reasonable amount of resource material provided and this one was no exception. Remember to use this information in your answers! Ignoring it, or – just as bad – copying bits rather than incorporating the material properly – is not a sign of a good response.)

I was particularly interested in this question because we used to look at the distribution of various phenotypes, wet & dry earwax among them. The examiner provided information about the nature of the genetic information underpinning the two phenotypes, along with data about the global distribution of people with wet & dry wax in their ear canals, including a very helpful map. The following graphic is not that map, but is very similar – showing allele frequencies rather than the phenotype distributions used in the exam – & accompanies an excellent blog post on the Discover magazine site. The ‘A’ and ‘G’ represent the 2 alleles involved in determining the relative dampness of your earwax:

Earwax is wet unless an individual has Adenine (A) at a particular site instead of Guanine (G), in which case the wax becomes the dry form. People who inherit the version of the gene that has A from both parents have dry earwax. People who inherit two of the G versions, or one G and one A, have wet earwax.

The actual question asked candidates to

use biological knowledge, together with information from the resource material, to discuss:

  • the origins and inheritance patterns of dry earwax
  • the evolutionary factors that may have resulted in the present-day distribution of both types of earwax.

And as always, a successful candidate would address all parts of a question. Nor would they assume that the examiner ‘knows’ what they know – you do need to spell out your understanding.

So, for the first bullet point: we’re dealing with a substitution mutation, where a change in a single base (from G to A) has led to a single amino acid change in the final protein. That secretory protein’s function is altered so that the wax that’s produced is now ‘dry’. The mutation must have occurred in a gamete-producing cell, or at the least during meiosis, & subsequently entered the human population’s gene pool. We know it’s a recessive mutation as someone must be homozygous for the allele to express wet wax, while heterozygotes have dry earwax. And you could also add that it’s not a sex-linked mutation, because (as the resource material notes) the gene involved in wax secretion is found on chromosome 16.

The second part of the question requires you to relate the information on the distribution of ‘dry’ & ‘wet’ wax phenotypes to your knowledge of patterns of human dispersal (in this case, the ‘out-of-Africa’ model). The fact that there’s no ‘A’ allele in African populations suggests that this mutation must have arisen after our species started to spread out of Africa. Furthermore, it could well have appeared once a small founder population had arrived in China, with subsequent genetic drift removing the dominant (G) allele from that founder group – this would explain the very high frequency of the A allele (up to 100%) in that region. You could also argue the possibility of positive selection pressure on this version of the secretory protein (an idea critiqued by the author of the Discover blog post).

However, the A allele is also found at fairly high frequencies in other Asian countries – the most likely explanation here is that subsequent migration and interbreeding has introduced it to those populations (with 54% of Indians and 69% of Japanese now expressing the ‘dry’ phenotype). Until fairly recently there was only minimal migration from China into Russia & Europe, which accounts for the very low frequency of the recessive allele in those populations.

What about the Americas? Our current understanding is that humans migrated into North America from Asia via a land bridge across the Bering Strait, during a glacial period. (There’s an interesting discussion around this here, including some work done using a molecular clock based on mutations in the common human pathogen Helicobacter pylori to estimate migration paths & times.) In dealing with this part of the question, I can think of a couple of options: that the lower frequency of the A allele in native American peoples reflects a founder event where the allele was at lower frequency to begin with, & subsequent genetic drift; or that the A allele frequency originally reflected that in Asian populations, but was diluted by a significant drop in population size following European settlement & some later interbreeding with the settlers. Simiilarly, the low A frequency in non-native Americans simply reflects their relatively recent arrival from Europe.

Who’d have thought that the story of earwax could be so fascinating?

how old is a piece of string? Alison Campbell Aug 22

No Comments

Among other things, I like to knit. My mother got me started, years ago, & I worked up to quite complex Fair Isle patterns on jerseys & shawls. But the kids weren’t all that keen on wearing woolly stuff once all the new ‘manmades’ came on the market, & a well-made jersey lasts a Long Time (30 years, in the case of one of mine), so the knitting took a bit of a back seat & I’ve only recently got back into it.

Anyway, I was talking about my latest project ** with some friends and Renee said, "I greatly admire people who can take two sticks and some fluffy string and turn it into clothes." At which point I thought: I bet that from a cultural evolution perspective, you could characterise the invention of string as a rather significant innovation. After all, sans string (or some form of fibre – & this would include animal sinew as well as plant fibre) there’d be no woven fabrics; no sewn garments; no nets or string bags to catch things or carry the catch home; no bows (& thus no arrows); no adzes bound to hafts or knives to handles; no sticks tied together into tripods or shelter frames… 

By itself, the idea of twisting thread or cordage isn’t all that complex, in technological terms. But in cognitive terms? Well, that’s something quite different, because of the abstract thought required to generate concepts of what that string could be. And in addition, there’s the actual manufacturing complexity involved: 

Process complexity can be illustrated by the example of a bag made out of string consisting of twisted grass. In terms of materials, the bag simply consists of string, which in turn consists of grass, and it can be described as low in complexity. In terms of process, however, the bag might involve tying a series of knots for the main body of the bag, and a series of different knots for the mouth of the bag, with perhaps a drawstring as well, and is likely to require considerable time and skill to manufacture; in this respect, the bag is high in complexity (Rugg, 2011).

The problem is, of course, that fibres don’t tend to survive well over long periods of time: currently the earliest-known remains of actual fibre products date back ‘only’ around 34,000 years‘, which is still amazingly old for relatively easily-degraded materials.  (See also this earlier post of mine.) This is certainly nowhere near as long as the other artefacts with which they may have been associated, although those associated artefacts may still speak to the existence of fibre technologies.  For example, Shea & Sisk (2010) suggest on the basis of what appear to be ancient arrowheads that "complex projectile technology" (bows & arrows, but also spear-throwers & the darts they were used to fling) were developed at least 50,000 years ago (possibly even longer). 

These authors also suggest that the technological advances that fibres enabled may well have had a significant impact on our evolution and dispersal; for example, through improving hunting efficiency. These tools would also have made hunting less perilous, allowing hunters to kill at a distance  - & so, alas, also had an impact on our ability to kill each other. There’s an interesting graphic showing the interplay between genetic, environmental, cognitive & cultural factors and their potential for human expansion here.

So there you go, Renee: my bits of fluffy string (& perhaps even the two sticks I use with them) have a history that goes back at least 50,000 years :) 

G.Rugg (2011) Quantifying technological innovation. PaleoAnthropology 2011:154−165. Doi:10.4207/PA.2011.ART49 (NB written from a mathematical perspective)

J.J.Shea & M.L.Sisk (2010) Complex Projectile Technology and Homo sapiens Dispersal into Western Eurasia PaleoAnthropology 2010: 100−122. doi:10.4207/PA.2010.ART36

 

** This is what started the discussion.

how old is a piece of string? Alison Campbell Aug 22

1 Comment

Among other things, I like to knit. My mother got me started, years ago, & I worked up to quite complex Fair Isle patterns on jerseys & shawls. But the kids weren’t all that keen on wearing woolly stuff once all the new ‘manmades’ came on the market, & a well-made jersey lasts a Long Time (30 years, in the case of one of mine), so the knitting took a bit of a back seat & I’ve only recently got back into it.

Anyway, I was talking about my latest project ** with some friends and Renee said, “I greatly admire people who can take two sticks and some fluffy string and turn it into clothes.” At which point I thought: I bet that from a cultural evolution perspective, you could characterise the invention of string as a rather significant innovation. After all, sans string (or some form of fibre – & this would include animal sinew as well as plant fibre) there’d be no woven fabrics; no sewn garments; no nets or string bags to catch things or carry the catch home; no bows (& thus no arrows); no adzes bound to hafts or knives to handles; no sticks tied together into tripods or shelter frames…

By itself, the idea of twisting thread or cordage isn’t all that complex, in technological terms. But in cognitive terms? Well, that’s something quite different, because of the abstract thought required to generate concepts of what that string could be. And in addition, there’s the actual manufacturing complexity involved:

Process complexity can be illustrated by the example of a bag made out of string consisting of twisted grass. In terms of materials, the bag simply consists of string, which in turn consists of grass, and it can be described as low in complexity. In terms of process, however, the bag might involve tying a series of knots for the main body of the bag, and a series of different knots for the mouth of the bag, with perhaps a drawstring as well, and is likely to require considerable time and skill to manufacture; in this respect, the bag is high in complexity (Rugg, 2011).

The problem is, of course, that fibres don’t tend to survive well over long periods of time: currently the earliest-known remains of actual fibre products date back ‘only’ around 34,000 years‘, which is still amazingly old for relatively easily-degraded materials.  (See also this earlier post of mine.) This is certainly nowhere near as long as the other artefacts with which they may have been associated, although those associated artefacts may still speak to the existence of fibre technologies.  For example, Shea & Sisk (2010) suggest on the basis of what appear to be ancient arrowheads that “complex projectile technology” (bows & arrows, but also spear-throwers & the darts they were used to fling) were developed at least 50,000 years ago (possibly even longer).

These authors also suggest that the technological advances that fibres enabled may well have had a significant impact on our evolution and dispersal; for example, through improving hunting efficiency. These tools would also have made hunting less perilous, allowing hunters to kill at a distance  - & so, alas, also had an impact on our ability to kill each other. There’s an interesting graphic showing the interplay between genetic, environmental, cognitive & cultural factors and their potential for human expansion here.

So there you go, Renee: my bits of fluffy string (& perhaps even the two sticks I use with them) have a history that goes back at least 50,000 years :)

G.Rugg (2011) Quantifying technological innovation. PaleoAnthropology 2011:154−165. Doi:10.4207/PA.2011.ART49 (NB written from a mathematical perspective)

J.J.Shea & M.L.Sisk (2010) Complex Projectile Technology and Homo sapiens Dispersal into Western Eurasia PaleoAnthropology 2010: 100−122. doi:10.4207/PA.2010.ART36

 

** This is what started the discussion.

the origins of humans lie in a – ahem! – far-fetched hybridisation event? Alison Campbell Jul 22

37 Comments

Or maybe not.

The internet is a wondrous place: a source of information, of amusement, and – alarmingly often – of material that elicits a combination of ‘say what?’ and <head-desk>. And a hat-tip to PZ Myers for this particular example…

For it has been proposed (by the originator of this particular hypothesis, & further discussed on phys.org) that humans arose as the result of an interspecies hybridisation event, rather than the current model for human evolution that sees chimps and humans sharing a Last Common Ancestor 5-6 million years ago and following their own trajectories since that time.

The event? Hybridisation between great ape (specifically, chimpanzee) & wild boar.

?

?

?

Now, we know that hybridisation happens; that the ‘biological species concept’ is not an absolute. But these events are generally between reasonably-closely related species: hybridisation is quite common in the waterfowl, for example. But even in birds, where hybridisation is well-documented, it doesn’t appear to cross the lines between one taxonomic order and another. Yet the ‘pig+ape’ suggestion requires hybridisation between different taxonomic orders – orders that (so fossil & genetic evidence tell us) have been separate for between 79 & 87 million years.

Surprisingly, Dr McCarthy, a geneticist and the proponent of this novel hypothesis, doesn’t present much in the way of genetic data to support it. He does agree that, genetically, we are closer to chimpanzees than to any other mammal, but suggests that this is due to back-crossing (with the chimp parent) after the initial hybridisation event:

And why might one suppose that humans are backcross hybrids of the sort just described? Well, the most obvious reason is that humans are highly similar to chimpanzees at the genetic level, closer than they are to any other animal. If we were descended from F1 hybrids without any backcrossing we would be about halfway, genetically speaking, between chimpanzees and whatever organism was the other parent. But we’re not. Genetically, we’re close to chimpanzees, and yet we have many physical traits that distinguish us from chimpanzees.

Surely the simpler explanation – that we are genetically similar to chimps because we are sister species – is more likely. Especially since at least some of the differences between the two species can be explained by differences in timing of developmental stages (the relative proportions of face & skull, for example), which may be sheeted home to mutations in regulatory portions of the genome.

In addition, there are major differences both in chromosome number (38 in pigs, 46 in humans) and in the position of various genes on those chromosomes that would make successful gamete production in any hybrid unlikely in the extreme (always supposing the hybrid was actually viable) – PZ discusses this in more length.

But anyway, what about those physical traits that “distinguish us from chimpanzees” & supposedly reflect our shared heritage with pigs? There’s a long list here. Many of them relate to bipedalism; to me, it’s special pleading to suggest that (for example) the presence of large gluteal muscles in bipedal humans and in domestic pigs is evidence of a close evolutionary relationship (Animal Farm aside, there is a distinct lack of evidence for bipedal locomotion in suids – and strong evidence of selective breeding for large backsides in pigs destined to become bacon & pork). Hairlessness? Only in domestic pigs; anyone who’s watched a huntin’&fishin’ show on TV will have seen how hairy a wild boar is. Pigs & humans both have longer hind-limbs than forelimbs, & shorter digits (compared to chimps)? Well, ye-es, I guess so, but that’s hardly evidence for a close relationship; one could say the same of mice… Similarly, while humans & pigs may (usually) be particular about where they defecate, well, so are other animals; rabbits, anyone? As for “snuggling [snuggling???], tears, alcoholism “being shared features in humans & pigs but not chimps… chimps & humans both have an enzyme (alcohol dehydrogenase 4) that allows us to break down ethanol, and it seems that chimps can become addicted to alcohol if given the opportunity.

Also offered in evidence are those diseases which are rare in non-human primates: “heart attack, atherosclerosis, and cancer (melanoma)”. Since these are to some degree, age-related, their relative rarity (for they are not absent in apes) may be ascribed to differences in lifespan: chimps in the wild may not live long enough to develop them.

Annoyingly, I see that over at uncommondescent, this proposal has been presented as even more evidence that evolutionary biologists are Getting It Wrong!

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Perusing more of the macroevolution website, I found the suggestion that armadillos and pangolins evolved from ankylosaurs and stegosaurs (page 244 at that link). It would be interesting to hear a palaeontologist’s taken on that one, but the fact that dinosaurs had diapsid skulls while mammals are synapsid doesn’t help.

 

 

 

 

ancient jewelry Alison Campbell Jul 20

2 Comments

I don’t own much jewelry – probably because I’m not often inclined to wear it. And what I do have is mostly old, passed down from my mother & her mother before her. Old, but not anywhere near the age of the find reported in PLoS ONE by Marco Peresani and his colleagues (2013).

The authors begin by noting that

Neandertal symbolic behaviour is a controversial issue that has attracted much debate over the last thirty years

and this has certainly being the case, with arguments ranging from the proposition that Homo neanderthalensis had no symbolic behaviour at all, to suggesting that the available evidence implied a number of such behaviours. Peresani et al. cite a range of sources in support of the latter view, including finds of grave goods in Neandertal burials, and the use not only of pigments such as ochre, but also of containers for those pigments and tools used in processing them.

The paper describes a find from Fumane Cave in northern Italy, a site where archeologists have been working for 20 years on a 2.5m-deep series of deposits that range in age from 300,000 to around 50,000 years ago. The cave was inhabited by Neandertals and – more recently, Homo sapiens – and contains a range of stone tools and other cultural artefacts.

However, the authors focus on a find from a layer in the cave that’s associated with late Neandertal habitation, characterised by tools from what’s known as the Mousterian culture. And here they found a shell; a shell that would have been collected as a fossil:  Aspa marginata is common in Miocene & Pliocene fossil assemblages (23.3-5.3 million years ago) and could not have come from the early Jurassic rocks in which Fumane Cave formed (the Jurassic extended from 200-145 mya).

In addition, the shell itself appears to have been uniformly stained with red ochre (haematite) and quite possibly pierced so that it could be hung on a thong (& so presumably worn as a personal ornament). The evidence? The inner lip of the shell has a number of striations, not found anywhere else on the shell or on any shells in the reference collection that the researchers compared it to. They interpret these microscopic patterns as due to scratching, perhaps due to tiny abrasive fragments in the ochre, when the shell rubbed against a suspending sinew that passed through a (now missing) hole in the lip of the shell.

For the shell had been covered with red ochre. The evidence for this lies in tiny pits that formed over the shell’s surface soon after the snail died. And the pits are filled with iron oxide (haematite) – the researchers think that the originally the whole shell was deliberately stained red, & that subsequent wear & later erosion in the cave sediments removed the colour from the outer surface but not from the pits.

journal.pone.0068572.g006.jpg

From Peresani et al (2013): Figure 6: Outer surace of an Aspa marginata shell from the reference collection (a) and from the Fumane specimen (b-f) doi: 10.1371/journal.pone.0068572.g006

Their conclusion:

analysis of the Aspa marginata found in Fumane… shows that this fossil gastropod was collected by Neandertals… at a Miocene or Pliocene fossil outcrop, the closest of which is located more than one hundred kilometres from the site. The shell was smeared with a pure, finely ground hematite powder, probably mixed with a liquid. It was perhaps perforated and used as a personal ornament before being discarde, lost or intentionally left at Fumane Cave, some 47.6-45.0 [thousand years before the present day].

Thus, this discovery adds to the ever-increasing evidence that Neandertals had symbolic items as part of their culture. Future discoveries will only add to our appreciation of Neandertals’ shared capacities with us.

Peresani, M., Vanhaeren, M., Quaggiotto, E., Queffelec, A., & d’Errico, F. (2013) An Ochered Fossil Marine Shell from the Mousterian of Fumane Cave, Italy. PLoS ONE 8(7); e68572. doi: 10.1371/journal.pone.0068572

aquatic apes & custard elephants Alison Campbell May 14

2 Comments

The ‘aquatic ape’ hypothesis (it can’t be described as a theory) has been around for quite a while, & in fact I’ve blogged about it before. So I was sorry to hear that Sir David Attenborough, who’s done so much to promote conservation issues and enhance our understanding of the natural world, appeared to have given the idea some support. He’s certainly taken some flak for this (see here, for example), although at the same time other – ahem! – news outlets have picked up the ball and trotted off down the garden path with it.

Briefly, the aquatic ape hypothesis (I will NOT call it a theory) purports to explain the evolution of a number of aspects of our morphology: our relative hairlessness & the distribution of that hair, bipedalism, the way so many people like fish (I will put my hand up as an exception to this), distribution of body fat, & so on. ** Unfortunately for this particular just-so story, there’s good evidence that all these features did not evolve at the same time. Bipedalism, for example, pre-dates the chimp-human divergence, but the addition of fish to the diet seems to have appeared much later. Nor is there necessarily strong evidence of any links between a particular feature & the life aquatic. For example, while cetaceans are essentially hairless, seals, sealions and their relatives are covered with dense coats of fur.

Anyway, the hypothesis has recently been the focus of some entertaining parodies, among them the ‘space ape’ version (face-to-face copulation would really have been the only option, dontcha know? for otherwise the jetpacks would get in the way) and – as a conclusion to his explanation of why the aquatic ape idea doesn’t stack up – Henry Gee’s thought experiment involving the unlikely combination of elephants and custard.

Enjoy.

** “& so on” includes the sinuses in our skulls (another feature that reinforces our African origins). Apparently they provided a buoyancy aid – yet they’re found in all mammals regardless of habitat.

[EDIT] However, courtesy of one Smut Clyde I find that the aquatic ape proposal has nothing on this.

 

 

 

 

 

 

 

are humans still evolving (a repeat visit) Alison Campbell Mar 20

2 Comments

What follows is a piece I wrote (quite a while ago now) for students planning on sitting Scholarship Biology. It was intended to start them thinking :) I’ve just been asked to contribute to a panel discussion on RNZ around this subject, so thought it might be timely to re-post this article (I think time has been kind to it!).

Here’s a question to consider: are humans still evolving? What sort of evidence could we use to answer this question?

We do tend to view evolution as something that happened in the past, and see the study of evolution as a ‘historical’ science. But nothing could be further from the truth. Evolution is an ongoing process, and we can detect its influence on the present-day human gene pool just as easily as we can view the development of our species’ family tree.

Remember that evolution is essentially a change in a population’s gene pool, as the result of ‘drivers’ such as natural selection and genetic drift. And studies of present-day human evolution look just there, at our genes. Some of these studies are summarised in a [relatively] recent paper in Science (Michael Balter (2005) “Are humans still evolving?” Science 309: 234-237), which is the basis for this posting.

To some degree the answer to this question depends on whether we are talking about ‘western’ populations. In the developed world, the combination of modern medicine, new agricultural and technological techniques, and cultural changes have significantly reduced the effects of natural selection: individuals who in the ‘old days’ would have been removed from the population (by famine, warfare, or disease) without contributing to the gene pool, now survive and have children. But in the developing countries, people are still subject to these selection pressures, so it’s probably here that we should be looking for evidence of evolutionary change: the spread of alleles that give resistance to diseases such as malaria, for example.

In those parts of the world where malaria is endemic, anyone with a genotype giving resistance to malaria would be at a selective advantage: they’d be more likely to survive and reproduce, passing their advantageous combination of genes on to at least some of their children. The overlap between the geographic spread of malaria in Africa with the presence of the sickle-cell allele is an example: individuals heterozygous for this allele are at a selective advantage over unaffected individuals (and those homozygous for the allele) where malaria is present. And other gene loci also seem to be involved in resistance to malaria. Variants of the glucose-6-phosphate dehydrogenase gene (which is involved in cellular respiration), one of the Duffy blood group alleles, and one haemoglobin C allele are all more common where malaria is endemic.

Another example is that of the “CCR5” gene. This gene codes for CCR5, a surface protein on white blood cells that is also the docking site for the HIV virus. People homozygous for a mutation (‘delta 32’) in this gene are resistant to attack by HIV, and are thus at a selective advantage in areas where HIV, and AIDS, are common. Yet the mutation is most common in white Europeans, and very rare in other ethnic groups – including Africans. AIDS is far more common in Africa than in Europe, so these differences in allele frequency are difficult to explain – unless they are the result of some other selective pressure that predates the AIDS epidemic. Scientists have dated the origins of the delta 32 mutation to around 700 years ago, and the current hypothesis is that it provided protection against an epidemic disease of that time, perhaps plague or smallpox. Can you make a prediction about the future prevalence of this particular allele, given the relative frequency of AIDS in different parts of the world, and the availability of medical care for patients?

cloning neandertals – can we? should we? is it true? Alison Campbell Jan 23

5 Comments

The Telegraph has a story on the possibility of cloning Neanderthals, with the fetching headline: ‘I can create Neanderthal baby, I just need willing woman.’ (You can read the NZ version on Stuff.)

My first thought was ‘eeewww’. (And, as a friend commented, it’s stories like this that get science a bad name.) Once past that rather visceral reaction, various questions popped up: just how feasible is this? Really? Has the researcher given any consideration to the ethical issues such a proposal generates? What about (epi)genetics, ecology & so on? And – for the money – how much of this ‘story’ accurately reflects what the scientist who was interviewed actually said, & how much of it is.. er… down to a combination of poor translation (the original article was in German-language paper Der Spiegel) and journalistic license?

Let’s deal with the last first: it would appear that the Daily Mail is responsible for the form in which this story hit the English-speaking world (oh, why am I not surprised by this?). And indeed, one of the quotes attributed to Harvard geneticist Professor Church strongly suggests the journalist wasn’t paying attention:

The professor claims that he could introduce parts of the Neanderthal genome to human stem cells and clone them to create a foetus that could then be implanted in a woman.

‘Parts’ of the genome would give you a Neanderthal? Implanting a ‘foetus’? Hellooooo.

Prof. Church is very firm that he hasn’t actively sought out volunteers for any potential, very-much-in-the-future surrogacy program. Rather, he was speaking theoretically of what was possible now that the Neanderthal DNA sequence is known. That’s good to hear, but I can’t help thinking that a little forethought might have avoided this whole furore. Science & scientists don’t need this sort of press. And let’s face it, people are more likely to remember the shock! horror! of the original story than they are to recall the subsequent, much less ‘exciting’ correction.

On the ethics front, bringing back an extinct race of humans from the dead (apart from the fact that there’s a little bit of their DNA in most of us) strikes me rather as treating them as objects. And what would be the justification for that? While there’s plenty of evidence that there are individuals around today who view other people in much the same way (ie as objects with no real rights or feelings about what’s happening to them), that is hardly a moral justification for resurrecting the Neanderthals. (And, before someone ever got to the point of cloning, there’d have to be some very serious examination of the ethics of surrogacy in a situation such as this.)

And what of the fact that they’d be brought back to an environment quite different to the one to which natural selection had shaped them? For example, in addition to having a physique (& probably physiology) best suited to cold environments, any cloned Neanderthal would be lactose-intolerant. And, in life, Neanderthals would have had their own microbiome: their own suite of micro-organisms living on and in their bodies and affecting them on a daily basis. For this hypothetical cloned individual, what would be the effect on their health of a microbiome that didn’t ‘match’?

On the genetics front (& Grant or David might like to comment here), there is a big difference between knowing the complete Neanderthal base sequence (or at least, the base sequence derived from a handful of individuals) and having a nuclear genome in a form that can be inserted into an enucleate egg (or stem cell, which was the focus of part of Prof. Church’s discussion with Der Spiegel). Plus, that wouldn’t be enough – the mitochondrial DNA of the egg cell would need to be replaced with Neanderthal mtDNA. Not to mention the effect of epigenetics on expression of those Neanderthal genes.

Yes, definitely some good learning opportunities there. I must try & work some of them into my own classes.

Network-wide options by YD - Freelance Wordpress Developer