2生命的进化与适应2教材.ppt

三、生命的进化 地球生命起源于30亿年前的太古代，历经3次大爆发、4次大灭绝，从低等、简单到高等、复杂， 30亿年－原核生物， 20亿年的元古代－真核生物， 6亿年的古生代寒武纪－无脊椎动物， 5亿年的古生代奥陶纪－脊椎动物、陆生植物， 1.8亿年的中生代侏罗纪－原始哺乳类， 300万年的新生代更新世－猿人， 多细胞生物后的演化： 两个特点：一是个体结构与机能的进化，一是新物种的形成，由水生向陆生发展构成生态系统。 结构的进化： 5.4亿年前: 植物骨骼化，出现钙藻； 4.3亿年前:植物木质化维管系统形成，陆生维管植物诞生, 被子植物起源； 3.4亿年前: 动物躯体功能分化、保护支持系统出现，高级无脊椎动物诞生；呼吸系统形成、外骨骼特化，陆生节肢动物出现, 3.9亿年前:中枢神经系统集中、内骨骼形成，鱼类起源，呼吸系统发展、两栖类起源； 3.4亿年前:生殖系统进化（羊膜卵），陆生爬行动物出现； 2.1亿年前:体温调节发展温血动物出现；生殖方式进化、哺乳动物起源 ； 1.9亿年前:鸟类进化 有性生殖：有性生殖在高等生物是一种普遍存在的繁殖方式，与其相关的第二性征的分化、求偶行为、社会等级体系、情感的交流等构成了当今生物多样性的重要内涵，但起源尚不清楚。 SECRET LOVERS? Giardia Bares All: Parasite genes reveal long sexual history While it hasnt yet been caught in the act, a single-celled parasite has been ready for sex for billions of years. A new research finding provides evidence that sexual reproduction started as soon as life forms that have nuclei and organelles within their cells branched off from their structurally simpler ancestors. The parasite Giardia intestinalis is well known for causing a diarrheal disease that animals and people contract after drinking contaminated water. Many researchers consider this species to be one of the most ancient living members of the eukaryote, or true nucleus, lineage. To determine when reproduction via sperm and eggs originated, researchers took a close look at G. intestinalis mysterious reproductive life. They focused on the hallmark of sexual reproduction known as meiosis, the process that halves the number of an organisms chromosomes to make gametes such as sperm and eggs. Among available data on the G. intestinalis genome, the researchers searched for genes similar to those that control meiosis in other eukaryotes, including plants, animals, and fungi. The researchers analysis revealed that G. intestinalis possesses genes similar to those used for meiosis by other eukaryotes. At least 5 of those genes function only in meiosis, and 10 others have roles both in meiosis and other functions. Although the researchers did