DNA – Replicated Typo

Neanderthal-human Hybrids

Paul Mason and Robert Short have an article out called Neanderthal-human hybrids (I wonder what that’s about?). Here is the abstract:

Evidence from studies of nuclear and mitochondrial DNA extracted from Neanderthal fossils and humans points to fascinating hypotheses concerning the types of interbreeding that occurred between these two species. Humans and Neanderthals share a small percentage of nuclear DNA. However, humans and Neanderthals do not possess the same mitochondrial DNA. In mammals, mitochondrial DNA is exclusively maternally inherited. Taking into account an understanding of interspecific hybridity, the available data leads to the hypothesis that only male Neanderthals were able to mate with female humans. If Haldane’s Law applied to the progeny of Neanderthals and humans, then female hybrids would survive, but male hybrids would be absent, rare, or sterile. Interbreeding between male Neanderthals and female humans, as the only possible scenario, accounts for the presence of Neanderthal nuclear DNA, the scarcity of Neanderthal Y-linked genes, and the lack of mitochondrial DNA in modern human populations.

Paul Mason previously wrote about the topic over at Neuroanthroplogy, so I really don’t have much more to say on the topic, other than that I’ll get around to reading it over the next couple of days. I’m curious to see if the usual suspects in the genetics (Razib Khan), anthropological (Dienekes) and evolutionary (John Hawks) communities offer some food for thought on the topic.

For me, I’m actually more interested in Mason’s recent work on degeneracy… But that’s for a later post 😉

Intelligence: Darwin vs. Wallace

It’s Charles Darwin’s birthday today! He’s 202. So in celebration I’ve written a post on the still ongoing controversy which the theory of evolution by natural selection caused and is causing, specifically with regards to the emergence of human intelligence.

Alfred Russel Wallace is widely seen as the co-discoverer of the theory of evolution by natural selection. While Darwin had been formulating his theory from as early as the late 1830s, he kept quite about it for more than twenty years while he amassed evidence to support it. In 1858 Alfred Russell Wallace, a naturalist of the same time, sent Darwin a letter outlining for him a theory of evolution which very closely mirrored Darwin’s own. The pair co-presented their theory to the Linnaean Society in 1858 but due to Darwin’s long time amassing evidence and refining his ideas, it was his book, On The Origin of Species, which was published in 1859 and set Darwin’s name firmly in the history books as the discoverer of natural selection.

While Wallace’s part in the discovery of natural selection is far from undocumented or unknown, it is largely for presenting ‘the same ideas’ as Darwin for which he is known and what is rarely discussed in the differences in their ideas. In this post I will briefly discuss a new(ish) paper by Steven Pinker on the evolution of human intelligence and some the differences between the thinking of Darwin and Wallace on the subject.

Darwin, unsurprisingly, asserted that the abstract nature of human intelligence can be fully explained by natural selection. In opposition to this Wallace claimed that it was of no use to ancestral humans and therefore could only be explained by intelligent design:

“Natural selection could only have endowed savage man with a brain a few degrees superior to that of an ape, whereas he actually possesses one very little inferior to that of a philosopher.”(Wallace, 1870:343)

Unsurprisingly most scientists these days do not agree with Wallace on either the point that the human brain could not be the result of natural selection or that as a result of this problem it must have been a product of design by a higher being. It would be both dismissive and dull to leave the discussion at that however, which is where Pinker comes in. Despite Wallace’s argument probably coming to the wrong conclusion he does bring up some very interesting questions which need answering, namely that of; “why do humans have the ability to pursue abstract intellectual feats such as science, mathematics, philosophy, and law, given that opportunities to exercise these talents did not exist in the foraging lifestyle in which humans evolved and would not have parlayed themselves into advantages in survival and reproduction even if they did?” (Pinker, 2010:8993)

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Evolving Linguistic Replicators: Major Transitions and Grammaticalisation

Just before Christmas I found myself in the pub speaking to Sean about his work on bilingualism, major transitions and the contrast between language change and the cultural evolution of language. Now, other than revealing that our social time is spent discussing our university work, the conversation brought up a distinction not often made: whilst language change is part of language evolution, the latter is also what we consider to be a major transition. As you evolutionary biologists will know, this concept is perhaps best examined and almost certainly popularised in Maynard Smith & Szathmáry’s (1995) The Major Transitions in Evolution. Here, the authors are not promoting the fallacy of guided evolution, where the inevitable consequence is increased and universal complexity. Their thesis is more subtle: that some lineages become more complex over time, with this increase being attributable to the way in which genetic information is transmitted between generations. In particular, they note eight transitions in the evolution of life:

What’s notable about these transitions, and why they aren’t necessarily an arbitrary list, is that all of them share some broad commonalities, namely:

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More on Gene-culture coevolution

Ed Yong has a cool article on Genes and culture: OXTR gene influences social behaviour differently in Americans and Koreans. It has some interesting parallels, and contrasting conclusions, with my post last week. Key paragraphs:

Heejung Kim from the University of California has discovered a great example of this effect by studying a gene called OXTR (or the ‘oxytocin receptor’, in full). The gene creates a docking station for a hormone called oxytocin, which is involved in all sorts of emotions and social behaviours, from trust to sexual arousal to empathy.

Kim looked at a specific version of the OXTR gene, whose carriers are allegedly more social and sensitive. But this link between gene and behaviour depends on culture; it exists among American people, who tend to look for support in troubled times, but not in Korean cultures, where such support is less socially acceptable. Culture sets the stage on which the OXTR gene expresses itself.

OXTR varies from person to person, and the DNA ‘letters’ at particular spots can affect the way we behave. According to previous studies, people with a ‘G’ at one specific site tend to be more sensitive parents, more empathetic and less lonely than those with an ‘A’. But most of these studies have been done with white, Western people who are hardly representative of the world at large – in fact, they’re positively W.E.I.R.D. [My emphasis]

What conclusions can we draw from Neanderthal DNA pt.2

4. Nuclear DNA: Forays into 3 billion base pairs

4.1 Before Vi-80

The Vindija-80 (Vi-80) specimen is an important find for geneticists: it yielded a minimally contaminated sample and provided those first steps into Neanderthal genomics.

Previously, attempts at retrieving ancient nuclear DNA sequences proved to be a notoriously difficult process, plagued with problems of degradation, contamination and chemical damage (Hofreiter et al., 2001). Researchers also need to contend with quantities of nuclear genome available: for every nuclear genome there are approximately several hundred mtDNAs (Green et al., 2008). The severity of these problems, especially contamination, is magnified through Neanderthal genetic similarity with humans (Green et al., 2006). This is troubling because nuclear DNA presents far less variability than mtDNA (Russell, 2002). As a result, huge stretches of nuclear sequences are required to find a significant number of polymorphisms (ibid). Such implications meant that discovering endogenous DNA sequences requires sifting through a large corpus of “[…] more than 70 Neanderthal bone and tooth samples from different sites in Europe and western Asia” (Green et al., 2006, pg. 331).

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What conclusions can we draw from Neanderthal DNA pt.1

In recent times, genetic technology has progressed sufficiently to elucidate upon some of the questions normally preserved for archaeologists. One such question concerns the fate of a group of hominins that roamed Europe and East Asia for at least 250,000 years. During this time, this species adapted and endured some of the harshest environments on offer, all while showing signs of a unique culture. Only for them to suddenly disappear from the fossil record approximately 30,000 years before present (BP) (cf. Barton et al. 2007). So, what happened to our closest evolutionary relatives, the Neanderthals?

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Neanderthal Genome Published

…Well, 60% of the genome at least. Not much has been said yet in regards to the nitty gritty aspects of Svante and colleagues’ findings. No doubt John Hawks and many others will offer their own perspectives over the next couple of days. If you’re interested in the immediate gist then here’s a link to the press release. Also, here is a quote from the BBC offering a succinct summary:
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Toadflax flowers are cool

Other than sound like a character from Bucky O’Hare, Toadflax (Linaria vulgaris) are fascinating plants for several reasons. Taking centre stage though is how this plant potentially offers another method of inheritance beyond genes. We’re now entering the slightly confusing world of epigenetics.

See, a particular species of these toadflax plants come in two distinct flavours: one consists of white, symmetrically arranged petals, whilst the other form is yellow and has five-pointed stars. Interestingly, this variation is not directly due to their DNA. Rather, these observed differences, which by the way are inherited by the offspring, are due to molecular caps attached to their DNA. As Carl Zimmer explains in his brilliant essay for the New York times:
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