Selfish genes

News flash: "selfish" genes actually exist. They aren't simply a metaphor.

New Discovery Proves 'Selfish Gene' Exists (6/20/08)

A new discovery by a scientist from The University of Western Ontario provides conclusive evidence which supports decades-old evolutionary doctrines long accepted as fact.

Since renowned British biologist Richard Dawkins ("The God Delusion") introduced the concept of the 'selfish gene' in 1976, scientists the world over have hailed the theory as a natural extension to the work of Charles Darwin.

Although I think that the idea of the "selfish gene" was a nice way to conceptualize the situation, the above remarks seem to be a little hyperbolic. It's not clear that this theoretical insight was that Earth-shattering. And the adjective wasn't meant to be taken literally:

In studying genomes, the word 'selfish' does not refer to the human-describing adjective of self-centered behavior but rather to the blind tendency of genes wanting to continue their existence into the next generation. Ironically, this 'selfish' tendency can appear anything but selfish when the gene does move ahead for selfless and even self-sacrificing reasons.

Nobody seriously thinks that genes have psychological "wants" or "needs". It's just that the effect of a gene may resemble what might be conscious advantage-seeking behavior in a human.

Or then again, specific human behavior may have adaptive evolutionary value even if it's not consciously undertaken for personal advantage or evolutionary success. Indeed, many human motivators that might seem to be "wants" or "needs" may have beneficial evolutionary consequences that are different from the apparent immediate objective of the specific motivator. (Sex itself is the best example of this. Even though a few species succeed without sex.)

And on the other hand, behavior that outwardly appears altruistic can be undertaken for genuinely "selfish" reasons, such as the personal satisfaction that can be enjoyed, or perhaps even public and social acclaim. If such social reward reliably does ensue, the behavior may well have adaptive value for an individual and a social group. The literature is replete with discussions of such issues.

However all that may be, the research in focus here gives actual evidence of the existence of a gene in honey bees behaving selfishly. The gene (which still remains to be explicitly identfied) disadvantages ordinary worker bees by making them sterile, but at the same time contributes to the success of the colony by promoting reproductive success of the queen bee. The gene can be called "selfish" because it condemns most bees to a lifetime of drudgery, in order to promote its own survival through the success of the colony and its most elite member(s).

Because the 'selfish' gene controlling worker sterility has never been isolated by scientists, the understanding of how reproductive altruism can evolve has been entirely theoretical -- until now.

Working with Peter Oxley of the University of Sydney in Australia, Western biology professor Graham Thompson has, for the first time-ever, isolated a region on the honey bee genome that houses this 'selfish' gene in female workers bees.

This means that the 'selfish' gene does exist, not just in theory but in reality. "We don't know exactly which gene it is, but we're getting close."

Who ever suspected that Republican political philosophy existed among honey bees?

Tags: sociobiology, altruism

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Comb jellies, again

Comb jellies were in the news back in April, and I discussed that here. They're a lot like jellyfish, only different. In particular, they are now thought to be the closest living relatives of the earliest animals on this planet.

The most recent news is that, although the bodies of these animals appear primitive, their genetic machinery has interesting resemblances to that of more modern animals, including humans.

Genes key to the development of modern animals' body plans show up in primitive-looking comb jellies (6/6/08)

No one suspected that the primitive comb jellies — watery, rotund and nearly invisible sea creatures — would rely on an intricate interplay of genes to design their rudimentary bodies. Yet researchers got a surprise when they looked at the comb jelly’s genes. Scientists found pattern-making genes that, in most animals, plot out the position of the head, brain, limbs and rear ends during development. These “homeobox” genes turned on in a specific pattern in the comb jellies, even though these ancient sea creatures are headless, brainless, limbless and rear end–less, scientists show in the June Development Genes and Evolution.

Homeobox genes are genes that have specific genetic code sequences. The sequences code for portions of proteins (called homeodomains) that are in turn able to bind to DNA, so that the proteins act as transcription factors. These transcription factors are especially important in the process of embryonic development, as they determine the overall body plan of the organism. Homeobox genes aren't unique to animals. They're also found in plants and fungi.

However, although comb jelly homeobox genes are similar to those of other animals, and they have functions in comb jellies that are vaguely similar to their functions in other animals, there are important differences too:

Certain genes expressed in the mouths of comb jellies and in the heads of other animals could indicate that the comb jellies’ mouths correspond to the front-end of all animals (except for amorphous sponges), Martindale says. And it implies that the mouth region of an ancestral headless animal is in the same area where the first head eventually arose. Although comb jellies are using the same basic toolkit as other animals, they might be doing so in an entirely different way, Martindale says. Genes involved with limb formation in other animals were expressed at seemingly random points along the comb jellies’ throat-like pharynx, for example.

“Mice, flies and even cnidarians [jellyfish and sea anenomes, mainly] seem to be built on the same basic plan, but the sponges and comb jellies don’t fall into that mold,” Martindale says.

Tags: Ctenophora, homeobox

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Male homosexuality

Doesn't it really suck to be a religious adversary of homosexuality these days? All their favorite arguments against genetic predispositions in some people for same-sex attraction are crumbling into dust. But then, when has their position ever had a foundation in the use of reason?

One of the favorite arguments against homosexuality is that it couldn't survive evolutionary selection, since only male-female couples can reproduce naturally.

It has previously been shown (2004), by one of the same researchers involved with a follow-on study, that females in the maternal line of male homosexuals were more fertile than average. This suggests that such females have some genetic characteristics that at the same time help them have more offspring and also to have more male offspring with homosexual inclinations than the overall average. This should be enough to allow homosexual males to stay in the population at some level, even if they never actually have children of their own.

Of course, questions still remained. What evolutionary model of this situation would actually show statistically that homosexual males would continue to persist in the population? And what characteristics of certain females promote both higher fertility and higher proportion of homosexual male offspring?

There are now some answers:

Male Homosexuality Can Be Explained Through A Specific Model Of Darwinian Evolution, Study Shows (6/17/08)

An Italian research team, consisting of Andrea Camperio Ciani and Giovanni Zanzotto at the University of Padova and Paolo Cermelli at the University of Torino, found that the evolutionary origin and maintenance of male homosexuality in human populations could be explained by a model based around the idea of sexually antagonistic selection, in which genetic factors spread in the population by giving a reproductive advantage to one sex while disadvantaging the other.

Male homosexuality is thought to be influenced by psycho-social factors, as well as having a genetic component. This is suggested by the high concordance of sexual orientation in identical twins and the fact that homosexuality is more common in males belonging to the maternal line of male homosexuals. These effects have not been shown for female homosexuality, indicating that these two phenomena may have very different origins and dynamics.

Male homosexuality is difficult to explain under Darwinian evolutionary models, because carriers of genes predisposing towards male homosexuality would be likely to reproduce less than average, suggesting that alleles influencing homosexuality should progressively disappear from a population. This changed when previous work by Camperio Ciani and collaborators, published in 2004, showed that females in the maternal line of male homosexuals were more fertile than average.

It was necessary to consider specific models of traits and genetic inheritance in order to eliminate any (and possibly all) that were inconsistent with existing data:

Challenged by all these empirical data, the authors of the new study considered a range of different hypotheses for the genetic diffusion of male homosexuality. These included: the genetic maternal effects on sons, the heterozygote advantage (as is found in malaria resistance), and "sexually antagonistic selection." The latter is a particular aspect of Darwinian evolution, in which genetic factors spread in the population by giving a reproductive advantage to one sex while disadvantaging the other. ...

To discover and clarify the dynamics of the genetic factors for homosexuality, the researchers had to screen a large set of models and exclude them one by one. They concluded that the only possible model was that of sexually antagonistic selection. The other models did not fit the empirical data, either implying that the alleles would become extinct too easily or invade the population, or failing to describe the distribution patterns of male homosexuality and female fecundity observed in the families of homosexuals. Only the model of sexually antagonistic selection involving at least two genes -- at least one of which must be on the X chromosome (inherited in males only through their mother) -- accounted for all the known data.

The results of this model show the interaction of male homosexuality with increased female fecundity within human populations, in a complex dynamic, resulting in the maintenance of male homosexuality at stable and relatively low frequencies, and highlighting the effects of heredity through the maternal line.

It makes a lot of sense, when you stop to think about it for even a moment, that a genetic factor favoring male homosexuality should be on a chromosome (X) that females have one more copy of than males. In that way, the factor can potentially be inherited, regardless of what her mate's genetics are. It also helps if the genes, whatever they are, tend to make female offspring more fertile, even if the male offspring are less fertile (because of homosexuality).

So what sort of characteristic might it be that favors females by making females more likely to reproduce but males less likely? Another report on this research spells it out:

"Gay Genes" May Be Good for Women (6/18/08)

Camperio Ciani's team suggests that these gay genes may actually increase how attracted both men and women are to men rather than making gay men more "feminine," as some researchers had earlier proposed. Although this is bad for male fertility, it is good for female fertility and allows such genes to survive at low but stable rates in a population, the authors say.

Dean Hamer, a behavioral geneticist at the National Cancer Institute in Bethesda, Maryland, who pioneered the search for gay genes, calls the study "an elegant mathematical analysis." He adds that the team has come up with a "simple solution" to the Darwinian paradox posed by homosexuality: "What is a 'gay gene' in a man is a 'superstraight gene' in a woman," he says.

With the evolutionary questions about male homosexuality out of the way, it's interesting to note that there is also recent evidence about the physiological nature of it. That is, there are physical differences between the brains of homosexual and non-homosexual individuals, both male and females. And further, the brains of homosexual individuals are different in ways that make them more like the brains of non-homosexuals of the opposite sex.

Symmetry Of Homosexual Brain Resembles That Of Opposite Sex (6/17/08)

Swedish researchers have found that some physical attributes of the homosexual brain resemble those found in the opposite sex. ...

Some psychological tests have shown differences between men and women in the extent to which they employ the brain’s hemispheres in verbal tasks. Other research has hinted that homosexuals may exhibit the tendencies of the opposite sex in brain behavior unrelated to sexual activity.

Ivanka Savic and Per Lindström, of the Department of Clinical Neuroscience at the Karolinska Institute in Stockholm, Sweden, now report that the brains of heterosexual men and homosexual women are slightly asymmetric — the right hemisphere is larger than the left — and the brains of gay men and straight women are not.

Positron emission tomography (PET) scans taken by the researchers also show that in connectivity of the amygdala (which is important for emotional learning), lesbians resemble straight men, and gay men resemble straight women.

A couple of remarks about this. First, these results don't have much to do with those of the research discussed earlier, in that they don't indicate how females who tend to have male homosexual children might be more attracted to men. But they aren't inconsistent, either. Second, although there are physiological differences, these could be due to exposure of the fetus to sex hormones in the womb, rather than to genetic factors.

In fact, it is possible that genetic factors aren't involved in male homosexuality per se. It could be that the genetic factors carried by females who tend to have male homosexual children are responsible for the hormonal environment in their wombs that pruduces both homosexuality and the brain differences just noted. But this may be unlikely, as the effect would have to be different, depending on the sex of the child – female children would still get brain characteristics atypical of females, yet the same attraction to males as their mothers have.

Sexuality is complicated.

More news reports about this:

• Gay brains structured like those of the opposite sex (6/16/08)
  
• Gay men, straight women share brain detail: report (6/16/08)
  
• Scans see 'gay brain differences' (6/16/08)
  
• Study Says Brains of Gay Men and Women Are Similar (6/16/08)
  
• Gay men and straight women have similar brains, study says (6/17/08)
  

An interesting question that still remains is: what does the evolutionary and physiological evidence say about female homosexuality? Not being lesbian, or even female, I don't have any particularly good insight into this. Just speculating, I would guess that the physiological factors tipping a female towards preferring another female rather than a male as a partner are complicated.

However, it could be as simple as that, as in the research discussed above, homosexual females have, like straight males, neural wiring that results in attraction to females. So that, consequently, there are few natural inhibitions, and some rewards, for females to seek other females for pair bonding.

Furthermore, since females can easily get pregnant with only brief (and usually ready, willing, and able) assistance from males, it would not be difficult for paired females to raise children together. Perhaps even less stress than trying to do the same with a male partner who has a roving eye. The males, for their part, might be just as happy not to assume the burdens of fatherhood, so they can go off hunting (for game, or more females) with their pals.

The evolutionary position of males and females who pair with their own sex just isn't symmetrical. Male couples cannot have children of their own, without the substantial assistance of a female for an extended period of time (especially if you count, as you must, a couple years for breast feeding.) But female couples just don't have such a problem. Life's not fair. This lack of similar evolutionary obstacles suggests a larger tendency towards bisexuality, at least, in females, which seems to be the case.

Update, 7/12/08:

A recent study of twins concluded that homosexuality results from a mixture of genetic and environmental factors: Homosexual Behavior Largely Shaped By Genetics And Random Environmental Factors.

A somewhat earlier study by one of the authors of the twin research found that male homosexuals navigate in virtual reality in a way similar to (straight) females: Gay Men Navigate In A Similar Way To Women, Virtual Reality Researchers Find

Update, 8/20/08:

Here's more recent research from Camperio Ciani and colleagues:

Bisexuality passed on by 'hyper-heterosexuals' (8/15/08)

Tags: homosexuality, evolution

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Comb jellies

I just thought it was sort of fascinating that comb jellies (also known as Ctenophorae), which aren't true jellyfish but are closely related, are now thought to be the oldest extant linage of the animal kingdom, usurping the title from sponges.

What's especially strange (though hardly inexplicable) is that comb jellies have some features that sponges lack, such as differentiated tissues and a nervous system.

The First Animal On Earth Was Significantly More Complex Than Previously Believed

A new study mapping the evolutionary history of animals indicates that Earth's first animal -- a mysterious creature whose characteristics can only be inferred from fossils and studies of living animals--was probably significantly more complex than previously believed.

Using new high-powered technologies for analyzing massive volumes of genetic data, the study defined the earliest splits at the base of the animal tree of life. ...

Among the study's surprising findings is that the comb jelly split off from other animals and diverged onto its own evolutionary path before the sponge.

How could it be that comb jellies are notably more complex than sponges, in spite of having appeared earlier?

Dunn says that the comb jelly could only have achieved its apparent seniority over the simpler sponge via one of two new evolutionary scenarios:

1. the comb jelly evolved its complexity independently of other animals, after it branched off onto its own evolutionary path; or
2. the sponge evolved its simple form from more complex creatures -- a possibility that underscores the fact that "evolution is not necessarily just a march towards increased complexity," says Dunn. "This scenario would provide a particularly dramatic example of that principle."

The evidence that comb jellies emerged earlier than sponges comes from intensive analysis of genetic data. The general idea is that detailed computer analysis comparing the DNA of different species indicates which species emerged earlier or later. As the researcher explains:

"Even though we looked at fewer than 100 species, they were sampled in such a way that they inform the relationships of major groups of animals relative to each other. Therefore, this study, and others like it, will have implications for the placement of far more species than just those that are sampled."

A somewhat earlier announcement is slightly more specific about what the researchers did:

Tree Of Animal Life Has Branches Rearranged, By Evolutionary Biologists

A study led by Brown University biologist Casey Dunn uses new genomics tools to answer old questions about animal evolution. The study is the most comprehensive animal phylogenomic research project to date, involving 40 million base pairs of new DNA data taken from 29 animal species.

Speaking of jellyfish-like creatures, I highly recommend Jelly Music.

Further reading:

Shock: First Animal on Earth Was Surprisingly Complex – another news report of the research

Phylogenetic fallacies: "early branching equals primitive" – blog post that cautions against certains misinterpretations of genomic data

Genomicron: Phylogenetic fallacies: “early branching equals primitive” – another blog post, elaborating on the preceding one

Tags: Ctenophora

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Metathoughts about brains

It occurs to me that there is an interesting connection between the two posts tonight. (This and this.) The first touches on the evolutionary origins of brains as sensory organs. The second (or rather, some references it contains) shows how sensory functions of human brains are still expanding – into huge space telescopes and even huger devices to sense gravitational waves.

Worth thinking about?

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Origins of brains as sensory organs

Recently (well, not too long ago) I posted (here) a bit about how elements of the modern nervous system of vertebrates can be traced back to some of the most primitive animals – sea sponges.

Now it transpires that the origins of specific brain subsystems can also be found in invertebrates. In this case, the subsystem is the hypothalamus. One of the interesting things about the hypothalamus is that it is not only an important part of the central nervous system, but also part of the endocrine system. As such, it causes production of a number of important hormones itself, such as melatonin, oxytocin, and corticotropin-releasing hormone. It is further tied into the endocrine system via its direct connection to the nearby pituitary gland. Some of these hormones appear to have invertebrate origins the same as the hypothalamus itself:

Modern Brains Have An Ancient Core

Hormones control growth, metabolism, reproduction and many other important biological processes. In humans, and all other vertebrates, the chemical signals are produced by specialised brain centres such as the hypothalamus and secreted into the blood stream that distributes them around the body.

Researchers from the European Molecular Biology Laboratory [EMBL] now reveal that the hypothalamus and its hormones are not purely vertebrate inventions, but have their evolutionary roots in marine, worm-like ancestors. In this week's issue of the journal Cell they report that hormone-secreting brain centres are much older than expected and likely evolved from multifunctional cells of the last common ancestor of vertebrates, flies and worms.

The invertebrate in question here is the marine ragworm Platynereis dumerilii. And if the foregoing findings weren't interesting enough, it seems that not only vertebrates share a common ancestor (Urbilateria) with P. dumerilii, but so too do insects and other worms. Furthermore, P. dumerilii has two types of light-sensing cells – one type of which is found in insects, and the other is found in vertebrates.

Marine Worm Has Insectile and Vertebrate 'Eyes'

Scientists today believe that the eye could evolve from a single light-sensing cell. Scientists disagree over whether it evolved just once, or many times.

It turns out that Nature is both creative and generous with her gifts. Recent research has shown that the tiny marine worm Platynereis dumerilii has two types of light-sensing cells. The eyes of the worm have rhabdomeric photoreceptors, a compound lens formation that is seen almost exclusively in insect eyes. Rhabdomeric photoreceptors are covered in little finger-like protrusions. In its brain, however, it has a different kind of light-sensing cells - ciliary cells that are seen in vertebrate animals. Ciliary cells have hair-like cilia that extend outward and branch out like tiny umbrellas. Two different ways of sensing light in a single organism!

In light of this circumstance, the following, from the first-mentioned research announcement, is especially interesting:

Both of the cell types studied in Platynereis and fish are multifunctional: they secrete hormones and at the same time have sensory properties. The vasotocin-secreting cells contain a light-sensitive pigment, while RF-amide appears to be secreted in response to certain chemicals. The EMBL scientists now assume that such multifunctional sensory neurons are among the most ancient neuron types. Their role was likely to directly convey sensory cues from the ancient marine environment to changes in the animal's body. Over time these autonomous cells might have clustered together and specialised forming complex brain centres like the vertebrate hypothalamus.

"These findings revolutionise the way we see the brain," says Tessmar-Raible. "So far we have always understood it as a processing unit, a bit like a computer that integrates and interprets incoming sensory information. Now we know that the brain is itself a sensory organ and has been so since very ancient times."

Tags: hypothalamus, endocrine gland, hormones

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Origins Of Nervous System Found In Genes Of Sea Sponge

One of the things that's always fascinating (or inspiring, astonishing, awe-inspiring – take your pick) about what we learn from the evolutionary history of living critters is how much very different sorts of living things have in common. This even reaches down to the level of single cells, where very similar genes can be found in mammals and yeast, even bacteria.

We also find complex subsystems with substantial similarities. So much so that the nervous system of the roundworm Caenorhabditis elegans, which has all of 302 neurons in its whole nervous system (hermaphrodite version), is routinely used as an experimental model for the nervous systems of much more complex animals.

Perhaps even more astonishing than that, however, is that it now appears some genes important for modern nervous systems existed even before there were nervous systems – in sea sponges, which are just about the most primitive animals known.

Origins Of Nervous System Found In Genes Of Sea Sponge

Scientists at the University of California, Santa Barbara have discovered significant clues to the evolutionary origins of the nervous system by studying the genome of a sea sponge, a member of a group considered to be among the most ancient of all animals.

And not only are some of the genes there, but the proteins they represent may have interacted similarly to the way that corresponding proteins interact in modern synapses.

"It turns out that sponges, which lack nervous systems, have most of the genetic components of synapses," said Todd Oakley, co-author and assistant professor in the Department of Ecology, Evolution and Marine Biology at UC Santa Barbara.

"Even more surprising is that the sponge proteins have 'signatures' indicating they probably interact with each other in a similar way to the proteins in synapses of humans and mice," said Oakley. "This pushes back the origins of these genetic components of the nervous system to at or before the first animals ---- much earlier than scientists had previously suspected."

Other blog articles: here

Original research paper: here

Tags: synapses, neuroscience

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What makes humans smarter than chimps?

Why have geneticists considered complete sequencing of the genomes of a variety of species so important? One reason (of many) is what we learn by comparing these other genomes with the human genome. And if you consider the genome of a close relative of humans, such as our closest relatives, chimpanzees, the comparison may be particularly enlightening.

The complete sequencing of the chimp genome was announced in August 2005. In May of this year, some results from comparing human and chimp genomes started to emerge:

Chimpanzee study reveals genome variation hotspots

Researchers believe that dynamic regions of the human genome - "hotspots" in terms of duplications and deletions - are potentially involved in the rapid evolution of morphological and behavioral characteristics that are genetically determined.

Now, an international team of researchers, including a graduate student and an associate professor from Arizona State University, are finding similar hotspots in chimpanzees, which has implications for the understanding of genomic evolution in all species.

That's an interesting clue, but it still doesn't tell us much about what accounts for the difference between human and chimp brains. More specifics about this came out three months ago, in August:

Scientists Find Brain Evolution Gene

Scientists believe they have found a key gene that helped the human brain evolve from our chimp-like ancestors. In just a few million years, one area of the human genome seems to have evolved about 70 times faster than the rest of our genetic code. It appears to have a role in a rapid tripling of the size of the brain's crucial cerebral cortex, according to an article published Thursday in the journal Nature.

Study co-author David Haussler, director of the Center for Biomolecular Science and Engineering at the University of California, Santa Cruz, said his team found strong but still circumstantial evidence that a certain gene, called HAR1F, may provide an important answer to the question: "What makes humans brainier than other primates?" Human brains are triple the size of chimp brains.

But that's only the beginning of the story:

Scientists Identify Gene Difference Between Humans and Chimps

Although this research does not definitively link this region to brain differences between humans and our closest relatives, it is intriguing. "We don't know what it does, and we don't know if it interacts with reelin, but the evidence is very suggestive that this gene is important in the development of the cerebral cortex, and that's exciting because the human cortex is three times as large as it was in our predecessors," notes team leader David Haussler of the University of California, Santa Cruz. "Something caused our brains to evolve to be much larger and have more function than the brains of other mammals."

And, of course, this is just the first of the 49 rapidly evolving regions to be studied. "Now we have to go through the other 48," Haussler says.

Sure enough, other interesting things are being found in other regions of the human genome that have evolved rapidly. This came out in October:

DNA trail points to human brain evolution

The human brain may have evolved beyond that of our primate cousins because our brain cells are better at sticking in place, researchers say.

A new study comparing the genomes of humans, chimps, monkeys and mice found an unexpectedly high degree of genetic difference in the human DNA regions that influence nerve cell adhesion, compared with the DNA of the other animals.

Accelerated evolution here allowed human brain cell connections to form with greater complexity, enabling us to grow bigger brains, the researchers suggest.

Ah ha. So enhanced adhesion between neurons facilitates bigger brains. That makes sense. But the story gets even more interesting, because apparently it's not only specific genes that play a role in this, but certain noncoding DNA regions between genes do also:

Looking for Smarts Between the Genes

The strongest evidence for accelerated evolution on the human line was found in noncoding sequences next to genes involved in helping neurons adhere to each other. The team found 69 such sequences, suggesting that changes in these regulatory elements may have contributed to the evolution of uniquely human cognitive talents.

Neuronal adhesion molecules play a major role in wiring the brain, Rubin says, such as the formation of connective synapses between nerve cells. These processes, he adds, are important in early brain development and also crucial for learning, memory, and cognition in adults. For example, Rubin says, one of the noncoding sequences is next to a gene called CNTN4, which appears to be involved in the development of both verbal and nonverbal communication abilities in humans, while another is adjacent to CHL1, which is linked to cognition in both humans and mice.

So this links up with another famously intriguing question: why is it that more than 90% of the human genome is made up of gaps between genes, gaps that don't seem to code for any proteins? Researchers have begun to suspect that some of this noncoding DNA consists of regulatory sequences that can affect, in different ways, when different genes are "expressed" and actually able to produce specific proteins. Looks like some of this noncoding DNA is important enough to help account for the rapid evolution of human brains.

I have the feeling we're just seeing the beginning of research findings in this area, and we're about to be hit by an avalanche of it. Here's another study reported just this week. It involves not just single genes, but entire networks of interconnected genes:

Unraveling where chimp and human brains diverge

By evaluating the correlated activity of thousands of genes, the UCLA team identified not just individual genes, but entire networks of interconnected genes whose expression patterns within the brains of humans varied from those in the chimpanzee.

"Genes don't operate in isolation – each functions within a system of related genes," said first author Michael Oldham, UCLA genetics researcher. "If we examined each gene individually, it would be similar to reading every fifth word in a paragraph – you don't get to see how each word relates to the other. So instead we used a systems biology approach to study each gene within its context."

The scientists identified networks of genes that correspond to specific brain regions. When they compared these networks between humans and chimps, they found that the gene networks differed the most widely in the cerebral cortex -- the brain's most highly evolved region, which is three times larger in humans than chimps.

Secondly, the researchers discovered that many of the genes that play a central role in cerebral cortex networks in humans, but not in the chimpanzee, also show significant changes at the DNA level.

Since there are probably scores of genes implicated in human-chimp brain differences, organized in different networks, I expect we're going to see research on this come out for some time to come.


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Additional information:

Accelerated Evolution of Conserved Noncoding Sequences in Humans

This is the abstract of the article in Science which describes the research about the importance of noncoding DNA for human brain evolution. (Subscription rqd for access to full text of the article.)

Scientists Explore Function of 'Junk DNA'

Via Evolution Research, this is a recent (like, last two days) news item on research into noncoding DNA that works by coding for microRNA.

Tags: biology, neuroscience, human evolution, noncoding DNA

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