为什么进化的速度以及复杂性变得越来越快？根据化石记录显示，单细胞生物于35亿年前首次出现在地球上，但是之后它们用了大约25亿年进化成多细胞生物，剩下的10亿年却发展成了植物、哺乳动物、昆虫、鸟类等各种各样的地球物种。
Rice大学科学家的研究结果可望解决这一问题，他们认为生物进化速度的加快是因为细菌和病毒不断在不同物种之间传递DNA，如果没有这种作用，只依靠基因突变和两性选择作用是不会达到如此快速度的。
Rice大学的Michael Deem说：“我们创造了第一个能解释物种间基因交换的进化数学模型。”结果发表在了1月29日的《Physical Review Letters》上。过去的数学模型主要关注生物如何对点突变做出反应，很少的理论关注再结合过程。
基因水平转移（HGT）是物种间的基因转移，是DNA从一个物种转移另一个物种。在50年前这一想法首次被提出时受到科学家的嘲笑，但是细菌抗药性的出现以及其它的很多发现，包括细菌用来交换基因的特定蛋白使这一理论在最近逐渐被接受。
Deem说：“我们知道动植物的很多DNA来自HGT过程，包括人类。”这一由Deem和Jeong-Man Park创造的新型模型用来解释HGT过程对于进化动力学的影响。过去的模型只能解释点变异，Deem和Park的模型显示了HGT如何通过传递变异增加进化的速度。
在一月的《Physics Today》上，Deem就描述了HGT的重要性，例如帮助细菌拥有对抗抗生素的抗药性等。
部分英文原文：
A Physical Theory of the Competition that Allows HIV to Escape from the Immune System
Guanyu Wang1,2 and Michael W. Deem1
1Department of Bioengineering and Department of Physics & Astronomy,
Rice University, Houston, TX 77005–1892, USA
2Department of Physics, George Washington University, Washington, D.C. 20052, USA
Competition within the immune system may degrade immune control of viral infections. We
formalize the evolution that occurs in both HIV-1 and the immune system quasispecies. Inclusion
of competition in the immune system leads to a novel balance between the immune response and
HIV-1, in which the eventual outcome is HIV-1 escape rather than control. The analytical model
reproduces the three stages of HIV-1 infection. We propose a vaccine regimen that may be able to
reduce competition between T cells, potentially eliminating the third stage of HIV-1.
Our immune system is highly effective in suppressingmost viral infections, due to the many different T cells that exist in the repertoire of one person. While many different T cells can recognize a virus, only those of highest affinity respond in large numbers and participate in eliminating the virus. One limitation of our immune system stems from the competition among T cells of similar specificity for the virus. For a series of discrete infections over time, competition in the immune system is associated with the phenomenon of deceptive imprinting [1], or original antigenic sin, and has been characterized by a random energy model [2]. Original antigenic sin is the tendency for memory immune cells produced in response to a first viral infection to suppress the creation of new immune cells in response to a second infection with a related strain. Moreover, while they are used, these memory immune cells may not be optimal for control of this second, different viral strain. Another form of competition in the immune system occurs when several viral strains simultaneously infect one person. In this case, the T cells compete to recognize the different strains, and
recognition of all strains may not be uniformly effective. This immunodominance of one strain over others means
that the immune response to multiple infections is not a simple superposition of the responses to each individual
infection [3].
更多原文链接：http://arxiv.org/abs/q-bio.PE/0610018
生物进化中的关键基因片断
单细胞生物进化研究的进步
悄然改变地球生物进化方向的污染进化
生物进化有十大奇迹
关于微生物进化的新认识
中国科学家探索生物进化机制的新发现
远古海洋可能极度缺氧 生物进化缓慢有因
生物性进化研究最新进展
