Friday, March 07, 2008

Genes and Our Evolutionary History

Over on my right "Links" sidebar you will find a link to the informative and entertaining video on "Becoming Human". The video tells the amazing story of our evolutionary development, a story spanning over 4 million years.

The latest issue of PNAS has this interesting article which examines the genetic underpinnings of key phenotypic features that are distinctive of humans, like our enlarged cerebral cortex and long life spans.

Appreciating the complex interaction between our biology and our environment is important for a variety of reasons. Understanding how we arrived at the situation we are now at helps us appreciate how incredible the achievement of just being here is in the first place! But it also helps us appreciate the possibilities that may be open to us as we aspire to push human evolution into new frontiers through the application of new biomedical interventions (like gene therapy or enhancement). Frontiers that go further than the current limitations we have inherited from our evolutionary past.

We live in truly fascinating times. And this article in the latest issue of PNAS further illustrates how fast things are moving in terms of putting together the pieces of our evolutionary past. Here is the abstract:

"Distinct genomic signatures of adaptation in pre- and postnatal environments during human evolution"
By Monica Uddin, et. al.

The human genome evolution project seeks to reveal the genetic underpinnings of key phenotypic features that are distinctive of humans, such as a greatly enlarged cerebral cortex, slow development, and long life spans. This project has focused predominantly on genotypic changes during the 6-million-year descent from the last common ancestor (LCA) of humans and chimpanzees. Here, we argue that adaptive genotypic changes during earlier periods of evolutionary history also helped shape the distinctive human phenotype. Using comparative genome sequence data from 10 vertebrate species, we find a signature of human ancestry-specific adaptive evolution in 1,240 genes during their descent from the LCA with rodents. We also find that the signature of adaptive evolution is significantly different for highly expressed genes in human fetal and adult-stage tissues. Functional annotation clustering shows that on the ape stem lineage, an especially evident adaptively evolved biological pathway contains genes that function in mitochondria, are crucially involved in aerobic energy production, and are highly expressed in two energy-demanding tissues, heart and brain. Also, on this ape stem lineage, there was adaptive evolution among genes associated with human autoimmune and aging-related diseases. During more recent human descent, the adaptively evolving, highly expressed genes in fetal brain are involved in mediating neuronal connectivity. Comparing adaptively evolving genes from pre- and postnatal-stage tissues suggests that different selective pressures act on the development vs. the maintenance of the human phenotype.