Thursday, February 7, 2008

Humans are still evolving

We are but a point on the thread of time
An interesting article “Sprinting down the evolutionary highway” written by Linda Hurst touches on an important realization that has been steadily emerging from the field of evolutionary sciences- humans are still evolving.

Steven Jay Gould once noted that “there’s been no biological change in humans in 40,000 years or 50,000 years. Everything we call culture and civilization we’ve built with the same body and brain.” Other eminent scientists through time have also supported the idea that human evolution has stopped or slowed to a trickle. The reasoning partly has something to do with reaching a “survival threshold”.

For example, 50,000 years ago modern humans made a “stunning leap forward” and began to develop a finely nuanced use of cooperative abstraction thereby giving birth to potent civilizations. The theory goes that upon having reached this level –a pivotal point where survival is reasonably assured- larger evolutionary pressures began to slow.

In fact, one way or another, the idea that the evolutionary process has somehow stopped or become just a side note for present day humanity has been, until recently, a popular notion.

Fantastic advances in genomic research are revealing just how wrong these assumptions have been. It appears that through the different recent developments of human civilization –the transition from hunter gathering to agriculture to the industrial revolution- biology and environment have been interacting at what seems to be an increasing pitch. In other words, it seems that evolutionary pressures for humanity have been –not static or stopped- but actually increasing for the last several thousand years.

John Hawks an anthropologist researching these issues notes “We are more different genetically from people living 5,000 years ago than they were different from Neanderthals.” His claim stems from studies he and others have done involving the analysis of 3.9 million genetic markers in 270 peoples from four groups (Han Chinese, Japanese, Africa’s Yoruba people, and northern Europeans).

They found evidence that about 1,800 recent mutations occurred in the last five thousand years representing qualities such as skin color and partial resistance to disease. This represents about seven percent of the human genome and suggests that there has been a steady accumulation of beneficial gene mutations occurring during this time. This is a rapid rate, far faster than previously thought possible.

It appears that part of the reason has to do with the above described level of human success. The transition to a changed diet, settled habitats, and higher survival (at least to breeding) rates did not slow evolutionary pressures; they pushed them to a higher level.

Apparently the exponential growth in human population from about five million to today’s six and a half billion has created a cauldron of possible evolutionary potential. As humanity spread throughout the world different groups have had to adapt to specific regional demands (i.e.; skin color, malaria resistance, HIV/AIDS resistance, dietary tolerances) thereby pushing evolution along. Also, the shear numbers of humans has allowed beneficial mutations to pop up more frequently, then rapidly spread through the population.

Mutations are spurious and accidental changes to an organism’s DNA that may or may not propagate throughout the species. Crudely speaking, if they offer a significant enough benefit, they become part of the established genome. What is especially interesting is that the general genetic “volume” or number of genes from where the incredible diversity of life originates is relatively small. The portion dedicated to constructing proteins- and essentially us- is even tinier. According to Olivia Judson “the proportion of a genome that contains the instructions to make proteins is tiny; in humans; it may be less that 2 percent. So there’s a lot of other DNA that will experience mutations.” She notes that a significant proportion of these could be dedicated to regulating and controlling how protein coding happens. For example, how these genes orchestrate the order, sequence, and timing of protein production represent the difference between a human or a lump of algae.

It is these “regulatory” genes that might provide a big clue towards understanding evolutionary change at the genetic level. It seems that beneficial mutational changes in these genes – those that manage and control the building block genes- might account for many of the evolutionary changes we are talking about here. In fact, there is more of a difference in complexity between these regulatory genes between species than there is between protein coding genes. These regulatory genes are like puppet masters manipulating a limited number of proteins in infinitely different ways producing the variety of life.

As important as mutations to the protein coding genes might be, there seems to be far more mutational potential and actual change occurring in the larger pool of regulatory genes. Fascinating examples include two noted changes in gene variation reported by geneticist Bruce Lahn that may have affected changes in brain complexity and size.

One change occurred over 37,000 years ago is now observed in seventy percent of the population and the other appeared only 5,800 ago has already spread to thirty percent of the population. Laun notes “Of particular interest are the ASPM and Microcephalin genes. In each of these genes, a new sequence variant arose in the recent past of human history and has since swept to exceptionally high frequency around the world, presumably because of strong positive selection operating on the new variant...These findings suggest the tantalizing possibility that the human brain is till undergoing rapid adaptive changes.” He adds that “Our environment and the skills we need to survive in it are changing faster than we ever imagined. I would expect the human brain, which has done well by us so far, would continue to adapt to those changes.”

These changes do not have to be great seismic events to affect the ebb and tide of human evolution. Part of the drive for this change is the inexorable interplay between genes and the selective pressures of a constantly changing environment.

The point is that evolution is not done with humanity by a long shot. As we peer deep into the inner workings of the gene, we find -to the consternation of some- that it is peering right back at us.

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