종의개념 Species Concept 종 에대한개념은분류학을넘어생물학전반에걸쳐서가장중심이되는개념이고, 종을정확히정의하고이의개념을적용하는것은생물학이라는학문에서제기하는많은의문점에대한답을제공하는것이다. 이에따라역사적으로수많은학자들이종을정의하고자노력하여왔지만, 아직까지정확한답은찾지못했으며종의실체에대한논쟁은현재까지지속되고있다.
비관속식물 관속식물 비종자식물종자식물일년생꽃식물 육상식물에서일어나는유전자흐름
일년생이형포자성식물 ( 포자와배우자생략 ) 일년생무성생식식물 육상식물에서일어나는유전자흐름
divergence lineage lineage segment lineage segment lineage segment
clade lineage lineage segment
Lineage sorting ( 진화계열소팅 ): 진화적분기이후한조상으로부터유래한여러유전자 lineage 가 lineage segment 내에서하나의 gene lineage 로수렴하는과정을말함. apomorphy apomorphy
Species: (1) 자연철학적인종의인식 Plato (BC 428/427 348/347) - idea론 : 형이상학이론. 이데아는현상세계밖의세상이며이데아는모든사물의원인이자본질이다. 예를들면인간의이데아는현실세계의인간에대한원인으로, 인간의이데아가있기때문에현상세계에인간이실재하는것을들수있다. - 현상세계에서모든것들은낡고사라지는것에반해, 이데아는시간에도그모습을변치않으며현상세계의사물들이궁극적으로되고자하는것. Aristotele (BC 384-322) - 종이란생물을이루는 idea를뜻하며, 개체는이러한 idea가물질을바탕으로하여구체적인실체가된것이라표현함.
Species: (2) 유형학적종의개념 (Typological species concept) = 분류학적종의개념, 형태학적종의개념, 원형적종의개념 Ray 로부터 Linne 까지 - Ray: 종의본질을과학적연구의대상으로써최초로인식 종이란생물의총화로서실제는형태적으로동일하고, 번식으로자손을퍼뜨리며상 호유사성을가진단위 - Linne: 체계적인명명법에의해자연계에존재하는모든생물이 종 이라는기본단위 로구별가능하게됨. 종은자연계에보편적으로존재하며, 지역적으로넓게분포하고있고, 분류의기본단 위가되며, 결코인위적으로창조된의식활동의산물이아니다 이후동종을대표할수있는하나의개체를형상 (eidos) 의원형 (archetype) 으로하여 기준으로삼는 Typological Species Concept ( 유형학적종의개념 ) 의출연. = Morphological Species Concept ( 형태적종의개념 )
Linne 에서 Darwin 까지 -Cuvier Species: (2) 유형학적종의개념 (Typological species concept) 만약종이변하는것이라면현재형태의독립성에의해규 정되고있는종의독립성은없어질것이고, 종간의경계가모 호해지거나소실되고말것임 - 종의존재에대한부정으로발전 무명론적종 (Nominalistic Species) : 존재하는것은개체뿐이다
진화론의대두 - Lamark : 종의가변성을구체적으로인식 종이란조금씩단계적으로형성되어나아가며, 변종은시간이지남에따라새로운종 으로발전한다 따라서생물의각분류계급은진화를통해형성되었고, 계통발생적인연속체 (continuum) 을이룬다. 종의실체를파악하여이론화시키지못함 - Darwin Species: (2) 유형학적종의개념 (typological species concept) 진화론 : 진화는종의변이성과자연선택에의해일어난다. 자연선택 (natural selection) 이란종의형성이외부환경조건에적응하기위하여전생 물이변해가는과정을설명하며, 여기에수반되는새로운종들사이의절연성 (hiatus) 의증대원인을규명하는것이다. 종자체에대한정의는명확하지않음.
Species: (3) 생물학적종의개념 (Biological Species Concept) 종은유전적집단으로구성되어있으며, 그집단을구성하는개체들은하나의생식적공동체 (reproductive community) 를이루고, 따라서그들은고유한생태적지위 (ecological niche) 를지님과동시에, 유전자 pool을공유하는유전적단위 (genetic unit) 가된다는기본적인인식을바탕으로함. Ernst Mayer (July 5, 1904 February 3, 2005) 에의한정의 상호생식적으로격리되며, 현실적또는기능적교배가가능한생물의자연집단군 A species is a group of interbreeding natural populations that is reproductively isolated from other such group.
Ernst W. Mayer Ernst Walter Mayr (July 5, 1904, Kempten, Germany February 3, 2005, Bedford, Massachusetts U.S.), was one of the 20th century's leading evolutionary b iologists. He was also a renowned taxonomist, tropical explorer, ornithologist, historian of science, and naturalist. His work contributed to the conceptual revol ution that led to the modern evolutionary synthesis of Mendelian genetics, systematics, and Darwinian evolution, and to the development of the biological spe cies concept. Neither Darwin nor anyone else in his time knew the answer to the species problem: how multiple species could evolve from a single common ancestor. Ernst Mayr approached the problem with a new definition for the concept species. In his book Systematics and the Origin of Species (1942) he wrote that a species is not just a group of morphologically similar individuals, but a group that can breed only among themselves, excluding all others. When populations of organis ms get isolated, the sub-populations will start to differ by genetic drift and natural selection over a period of time, and thereby evolve into new species. The mo st significant and rapid genetic reorganization occurs in extremely small populations that have been isolated (as on islands). His theory of peripatric speciation (a more precise form of allopatric speciation which he advanced) based on his work on birds, is still considered a leading m ode of speciation, and was the theoretical underpinning for the theory of punctuated equilibrium. Mayr is generally credited with inventing the modern philosop hy of biology, particularly of evolutionary biology, which he distinguished from physics, for its introduction of (natural) history into science.
생물학적종의개념의문제점 Species: (3) 생물학적종의개념 (Biological Species Concept) 1) 적용의한계성 : 식물들은많은경우생식의개념없이개체증식영양번식 (vegetative propagation) - 대부분의다년생피자식물에서일어남 Ex) Scandinvian flora 피자식물중 80% 이상이 vegetative propagation을함 (Gustaffson, 1964). Ex) Redwood tree (Sequoia sempervirens) 80% 이상이 crown sprout로기원. 20% 만이 seedling에의함. Ex) Populus tremuloides : 25 acer에 15,000개체를갖는 clone 형성 - 무수정결실 (agamospermy) : 배우체를만들지않고수정없이 embryo를만들어내는것. ex) 민들레속 (Traxacum) 식물 i) pathenogenesis ( 처녀생식 ): 수정없이 egg ( 알세포 ) 가 embryo 로발달 ii) adventitious embryony ( 부정배현상 ): ovule ( 자방, 씨방 ) 내의체세포가 embryo로발달 2) True breeding의문제점 - A X B 5% but B X A 98% - A X B, B X C, C X D, D X E 교배가능그러나 A X E는교배불가능
Populus tremuloides
Species: (4) 진화적종의개념 Evolutionary species concept Simpson (1961) 1) It is a lineage, an ancestral-decendant sequence of populations existing in space and time. 시공에존재하는일련의조상-후손집단들의연속으로서의계보. 2) The lineage evolves separately from other such lineages, that is, from other species. 다른종과같은다른계보로부터분리되어진화한계보. 3) It has its own unitary evolutionary role which is to say that it fits into its own particular ecological niche in a biotic community. 자신의독자적진화적역학 (evolutionary role) 을하는것, 즉생태계에서자신의특수한생태적지위로적응한집단. 4) It has its evolutionary tendencies, being susceptible to change in evolutionary role during the course of its history. 자신만의진화경향성을가져자신의역사경로동안진화적역할을변화시킬수있다. Wiley (1978) Common evolutionary fate through time 공통적인진화적운명을지닌집단
Species: (4) the others Recognition Species Concept ( 인지적종 ) Phenetic Species Concept ( 표현적 ) Apomorphy Species Concept ( 파생형질 ) Diagnostability Species Concept ( 진단적 ) Cohension Spicies Concept ( 연합적 ) Phylogenetic Species Concept ( 계통적 ) Genealogical Species Concept ( 혈통적 )
식물분류학에있어서교과서에나올만한유명한화석들
Archaeanthus >102MYBP Published in 1984 목련과닮은화석 - 시카고대학교의 Dr. Peter Crane 과플로리다대학교의 David Dilcher 에의해발견된화석으로목련의직접조상으로생각됨. - 그당시까지가장오래된피자식물의화석으로알려짐
Microvictoria svitkoana Gandolfo >90MY published by Dr. Friss in Upssla Univ. in 2001
Archaefructus liaoningensis 124.6MYBP Published in 1998 현재까지 알려져 있는 가장 오래된 피자식물 화석
Archaefructus sinensis 124.6MYBP Published in 2002 - 이전 것과 동일 장소에서 발견된 다른 종 - 재미있게도 물고기의 화 석과 같이 발견되어 수생식 물이 아니었을까 추정됨.
Leefructus 122.6-125.8 MYBP Published in April 2011 Eudicots에 대한 최초의 fossil record: 127-125 MYBP - 현재 eudicots에 해당하 는 발달한 미나리아재비 과 식물과 흡사함. - 이 화석은 Archefructus 와 연대가 거의 차이가 나 지 않고 있어서 피자식물 의 진화가 폭발적으로 다 양화가 일어났다는 것을 뒷받침하고 있음.
현생 진정쌍자엽식물 중 미나리아재비과 식물과 매우 유사
미나리아재비과의투구꽃