Wednesday, 17 June 2015
The Royal Society recently published a special issue of Philosophical Transactions B entitled Human evolution: brain, birthweight and the immune system, edited by Graham J Burton, Ashley Moffett and Barry Keverne. The interesting theme is summarized as follows:
"The complexity of the human brain is unique amongst mammals. However, the large size of the brain at birth poses risks to mother and offspring due to constraints on pelvic architecture and uterine perfusion imposed by bipedalism, the so-called ‘obstetric dilemma’. The growth of the human brain in utero is believed to be permitted by our unique highly invasive form of placentation. The structure of the placenta varies to a greater extent between different mammalian species than any other organ. In particular, there is a spectrum of invasiveness of the fetal tissues into the wall of the uterus, even amongst the apes. Invasion poses unique immunological challenges as the migrating trophoblast cells expressing paternal genes intermingle with cells of the maternal immune system in the uterine wall that must be negotiated. Recent advances have also revealed important insights into the genetic and epigenetic links between the regulation of placental and brain growth, centred on imprinted genes that are expressed in a parent-of-origin manner. This complex network of interactions regulating brain development is explored in this Theme Issue in the light of new concepts in placental evolution, the immune system at the maternal-fetal interface, and genomic imprinting."
The table of contents can be found here. Disclosure: I co-authored one of the papers.
Monday, 8 June 2015
|Macrauchenia - an extinct South American native ungulate|
Drawn by Kobrina Olga (Wikimedia Commons CC BY 3.0)
The authors used MALDI-TOF mass spectrometry to determine the amino acid sequences of the alpha chains of type I collagen extracted from fossil bones. They then performed a phylogenetic analysis. This showed that Macrauchenia and Toxodon form a monophyletic group. Interestingly, this resolved as the sister group to modern Perissodactyla, i.e. horses, tapirs and rhinoceroses. Together they form a taxon named Panperissodactyla.
The modern species have an epitheliochorial placenta so perhaps this type was present in the sister species Macrauchenia and Toxodon.
Thursday, 4 June 2015
|Sir Richard Owen (1804-1892)|
Placentalia was relaunched by McKenna and Bell in their influential volume Classification of Mammals above the Species Level (New York 1997). It is attributed to Sir Richard Owen (pictured above).
|Owen 1837 [sic] page 903|
In its current usage, Placentalia defines a crown group of mammals comprising extant species and their ancestors. It is not the same as Eutheria, which includes lineages that do not have living descendants. Placentalia therefore is popular in molecular phylogenetics and phylogenomics. The reason is evident: when working with DNA sequences from living species, inferences can be drawn only about character evolution in the crown group.
When looking for the Owen reference I found that McKenna and Bell had got the date wrong. Robert B. Todd commenced publication of The Cyclopaedia of Anatomy and Physiology in 1837 but Owen's article is in volume 4 part 2 published 1849-52 (full reference below).
Owen R. Teeth. In Todd R.B. (Ed.) The Cyclopaedia of Anatomy and Physiology Vol. 4 Part 2, pp. 864-935. London: Longman, Brown, Green, Longmans and Roberts, 1849-1852. McKenna and Bell Refer to page 903.