Friday, 19 July 2013

Evolution For Brainy People

Neanderthal. Why did we succeed and not him?
First look into workings of the Neanderthal brain - life - 17 July 2013 - New Scientist

It's beginning to look like our (Homo sapiens) ultimate and apparently quite sudden success over our close cousins the Neanderthals (H. neanderthalensis or maybe H. sapiens neanderthalensis) and the recently-discovered Denisovans who don't seem to have been awarded a scientific name yet, may have been due to changes in a very small number of genes, and maybe whether they were 'switched on' or not.

Incidentally, this same article illustrates how anatomical complexity need not involve increased genetic complexity, as Creationists wrongly claim the evolution theory says. In fact it doesn't even need to involve an increase in information, merely what that information is. I'll expand on this later.

Scientists working for the Hebrew University of Jerusalem and the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany have analysed the epigenomes of Neanderthals and Denisovans and compared them with those of modern humans and have found that there was about a 99% match. However, of those 700 or so which differed, about 200 of these were common to Neanderthals and Denisovans but where theirs were active ours were inactive, and vice versa. Many of these are involved with immunity and metabolism and, when they go wrong, with disease. A very large number seem to be associated with psychiatric and neurological conditions.

It may be worth me expanding on the term 'epigenome' before I go much further, if for no other reason than that it was new to me.

The epigenome is the system of chemical markers and attachments to DNA (the genome) which are involved with switching genes on or off. Every cell (with a few special exceptions like red blood cells which are more like packets of haemoglobin than true cells) have the same complement of genes as the original cell from which the organism developed, yet each different tissue requires just a subset of these genes. This is where the epigenome comes into play. Chemical markers, one of which is termed 'methylation', act as switches to turn off unwanted genes and to prevent them firing. One cause of diseases such as some cancers may be a mis-firing of genes cause by failure of the epigenome.

The epigenome can be inherited along with DNA, hence changes here can also be selected for or against by natural selection. For more on this see Epigenetics: DNA Isn’t Everything and What Is Epigenetics?

The fact that these epigenetic markers were present in Neanderthals and Denisovans but were reversed in modern humans suggest we evolved these differences after the first migration out of africa of a common ancestor (probably H. heidelbergensis) which then diverged into Neanderthals and Denisovans in Euro-Asia whilst our direct ancestors remained in Africa, and that this evolution included changes to the details of how our brains work.

This finding reinforces previous work at the Max Planck Institute for Evolutionary Anthropology by Svante Pääbo's team:
The findings complement previous studies. In 2012, Pääbo's team sequenced the Denisovan genome and found that humans have eight key gene variants not shared with Neanderthals or Denisovans that allow neurons to project further across the brain and connect with one another. They may have allowed our direct ancestors' brains to become more complex.

Taken together, the studies suggest that changes both in genetic sequences and in pattern of activation of the genes were crucial in enabling our ancestors to develop larger, more complex brains.

That may have helped give us our cognitive edge. For instance, genes and gene-expression patterns that conferred greater abilities in communication and social interaction, or changes in cognition, would have been evolutionarily advantageous for humans, says [Sarah] Tishkoff [University of Pennsylvania in Philadelphia, USA].

First look into workings of the Neanderthal brain, Sara Reardon, New Scientist Magazine issue 2926 18 July 2013
In the epigenomic regions that differ between species, the human brain contains almost five times as many genes that are linked to early brain development as would be expected by chance, Yi says. Defects in them are connected with problems in the early stages of brain development. Humans also have 3.5 times as many autism-related genes.

So while our brains have become bigger and more intelligent, it seems that evolutionary changes have also made our brains more prone to develop neurological conditions, such as autism and schizophrenia.

Sara Reardon, New Scientist, op cit.
Reporting the findings of Soojin Yi, et. al.
Georgia Institute of Technology, Atlanta, USA.
These findings have to be treated with some caution however, as they are based on analysis of the epigenomes of bone not brain tissue, where the epigenome may have been different, so projecting this into differences between ours and our cousin species brains is only speculative. Never-the-less, the commonality between Neanderthals and Denisovans and the differences they show compared to modern humans, and the implications that has for how and when we diverged still holds true.

To me, the amazing thing is how so much new information is coming from the recently-developed DNA sequencing work done by the Max Planck Institute for Evolutionary Anthropology and how it's adding so many of those missing pieces of the jigsaw puzzle.

We're now almost sure that there were at least two migrations out of Africa and that we are all descended (mostly) from those who remained behind to evolve further and then migrate out again, to find at least two cousin species already established in Europe and Asia with whom, for a brief period in our history we occasionally interbred successfully, much like a ring species showing incomplete speciation. And now we come a little closer to understanding why we eventually replaced them and became the sole survivors, albeit with a few genes which we who came out of Africa in the second wave inherited from them by hybridization.

Now, as for the notion that evolution of increased anatomical complexity involves increased DNA complexity, as per the standard Creationist misrepresentation of evolution theory, this work on epigenetics shows how a more complex brain could well have evolved not by any changes at all in the underlying genome but by simple changes in the epigenes controlling the DNA sequences which express as genes. The only change in information (not addition, but change) need only be the difference between 'on' and 'off' in a particular tissue. So no new complexity in DNA and no change in the amount of information present, merely a change in the meaning of that information.

One wonders how much longer the Discovery Institute loons and liars, and the Ken Hams, Kent Hovinds and Dwayne Gishes of this world are going to remain seated on the beach with their hands out, expecting the on-rushing tsunami of scientific evidence to comply with their requirements. It'd probably difficult to maintain that posture with one's head in the sand.

Further reading:
First look into workings of the Neanderthal brain (Subscription required for full article).
When The Conclusion Is Sacred Facts Must Be Ignored.
A Human Ring Species?
More Evidence For a Human Ring Species.

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5 comments :

  1. This is amazing stuff, and it appears that the findings are really recent.

    I read Bryan Sykes' "Seven daughters of Eve" a few years back (mostly about tracing relation through female mitochondrial DNA) a few years back, and in that book, he says that there was no evidence of interbreeding between homo sapiens and Neanderthals.

    While I was reading that book, i stumbled on an article about Ozzy Osbourne having Neanderthal DNA.

    This makes it sound as though interbreeding was fairly widespread for a time.

    Great stuff...

    ReplyDelete
    Replies
    1. It is very recent. Only the last couple of years since improved DNA sequencing was developed.

      Delete
  2. I think Katy Anders hit on an important part that theist tend to not want to think about either. That there was interbreeding between the species. If this is true then why did god allow the neanderthals to die out? Only conclusion god is vengeful/hateful/not-worthy or god does not exist.

    ReplyDelete
    Replies
    1. The reason why (especially) American fundamentalists and Muslims get so hysterical about evolution is because they know it completely destroys their notion of a species specially created by a god. In the case of Christians it also destroys to whole notion of an original sin committed by our two original ancestors and so the entire need for some sort of forgiveness and redemption. An evolved species does not have two original ancestors as there is no point at which that species can be said to have come into existence because evolution is normally a slow, gradual process spread over very many generations and involving the entire genepool, not an event.

      The real problem for the clerics is that this takes away the entire basis of their control and the reason for their existence. The clerics know that evolution makes them redundant and that their 'faith' is a sham.

      Delete
    2. Well said. Its amazing how some people (more progressive theists) also believe in evolution for all animals except humans. As if we are special and "god made?.

      Delete

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