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EVIDENCES OF ORGANIC EVOLUTION 

Some important evidences are – 

1.   Palaeontological Evidences – 

The study of fossils is known as    :  Palaeontology.

Fossils                                               :      Taken from Fossilis/Fossolium 

Father of palaeontology                  : Leonard da vinci

Founder of modern palaeontology :    George cuvier

Birbal Sahni is famous for Indian palaeonotology

Two branches of palaentology –

1.   Palaeobotany : Study of plant fossils

2.   Palaeozoology : Study of Animals fossils

Definition of Fossils was given by Charls Lyell ''Impression of past found in Rocks called fossils''  fossils provide one of the most acceptable evidence in support of organic evolution.

Type of Fossils :  

1.   Unaltered Fossils : 

In this type whole bodies of extinct organisms are found frozen in ice at the polar regions eg. Wooly mammoths (25000 yrs before extinct fossils were found from Siberian region) 

2.   Petrified fossils – Most common type of fossil.

Replacement of organic part by mineral deposits is called petrification.

These fossils consists of only the hard parts e.g. bones, teeth, shells, wood etc. of extinct organisms.

In human body first fossilization occurs of teeth.

Evidence of Evolution & Adaptive Radiation | Biology Class 12 - NEET

 

3.   Mould fossils – 

Here no part of the original organism is present, only an impression of the external structure of body is preserved in wet soil.

4.   Cast fossils – 

Sometimes minerals fills in the mould, resulting in cast fossils   

5.   Print Fossils – 

Foot print or prints of wings, skin,leaves, stems etc made in soft mud which subsequently become fossilized are a common type of fossils.

6.   Coprolites – 

These fossils include the fossil preservation of contents of the intestine or excreta of many ancient animals including particularly the reptiles or fishes.

By studying fossils following facts about organic evolution are evident –

1.   Fossils found in older rocks are of simple type and those found in newer rocks are of complex types.

2.  In the beginning unicellular protozoans were formed from which multi-cellular animals evolved.

3.   Some fossils represents connecting links between two groups

Evolution of Horse – 

Evolution of horse was described by C.marsh.

Evidence of Evolution & Adaptive Radiation | Biology Class 12 - NEET

Evidence of Evolution & Adaptive Radiation | Biology Class 12 - NEET

The primitive fossil of the horse was   found in North America named Eohippus.

Changes during evolution of horse are as follows –

1.   Increase in body height

2.   Increase in the length of neck

3.   Development of high crown on the surface of teeth and formation of cement.

4.   There is gradual increase in the length of  legs.

5.   Number of toes or fingers in legs have reduced in modern horse. Only middle toe touches the ground, other toes reduced gradually.  

6.   Legs become more powerful for fast running.

7.   As new species were formed, previous ones becomes extinct.

8.   Enlargement of brain size.

Fossils of important Ancestors of horse

1.   Eohippus or Hyracotherium – 

It evolved in Eocene Epoch.

It's size was like a fox.

(Orohippus : It evolved in middle Eocene epoch.)

2.   Mesohippus – 

It evolved from eohippus during Oligocene epoch.

It's size was like a sheep. 

(Miohippus : In the late oigocene Mesohippus was replaced by another slightly advanced horse like form named miohippus. It was much like mesohippus in a appearance but some what large in size)

(Parachippus : It evolved in early miocene).

3.   Merychippus – 

It evolved in middle and upper miocene epoch. It's size was like a donkey.

4.   Pliohippus – 

This horse evolved during pliocene epoch. It was of the size of modern pony.

5.   Equus – 

This is modern horse which evolved from pliohippus during pleistocene epoch (height 60-64 inches).

''Dating of fossils''  or ''The clock of the Rock''

The fossils give valuable information about the history of organic evolution by giving information about the organisms which existed in the past.

This is possible only if the correct age of the fossils can be determined. Methods have been developed to find out the correct age of the fossils by determining the age of the rocks  where the fossils are found.

Rocks have been found to contain certain radioactive elements which lose their radioactivity and change into other nonradioactive isotopes at a fixed rate irrespective of the environmental conditions prevailing at different times.

If the rate of this loss of radioactivity of an element is known, the relative proportions of the Quantities of radioactive and nonradioactive element in a given rock will enable us to find out the age of the rock.

This method is called absolute dating.

This will be illustrated with the help of four different methods.

(1) Lead method

(2) Radio-carbon method

(3)  Potassium – Argon method

(4)  Electron spin resonance method (ESR method)

Geological Time Scale – Firstly given by Giovanni Avduina.

Chronological order of the history of organic evolution, which is presented in the form of geological time scale.

This time scale includes the history of earth itself ever since it was formed to formation of its crust from lava of ancient volcanic eruptions.

The period between the origin of gaseous cloud (4.6 billion years ago) from which the earth was formed and the formation of earth's crust is called Azoic Era (era of no life).

The remaining period (about 4.0 billion years) is divided in to five Eras namely –

1.  Archaeozoic                           

2.  Proterozoic                                         

3.  Palaeozoic

4.   Mesozoic                                

5.   Coenozoic

The Archaeozoic Era had ''invisible life'' and the remaining four era had ''visible life'' (Phanerozoic). Archaeozoic and proterozoic eras are also grouped together as Precambrian because the first part of palaeozoic is Cambrian.

The three eras namely palaeozoic, mesozoic and coenozoic, each is further divided into smaller time spans called Period and the periods of coenzoic era are each further subdivided into Epochs.

It is also believed that each era of earth's history started with a revolution or cataclysm and ended with yet another revolution.

These revolutions meant intense geological disturbances that occurred on earth, so that most of the pre-existing organisms perished in each revolution and the few remaining ones evolved into new and varied organisms.

The first great revolution is believed to have occurred between archaeozoic and proterozoic eras.

The second great revolution between proterozoic and palaeozoic eras.

Applachian revolution between palaeozoic and Mesozoic eras.

Finally the rocky mountain revolution between Mesozoic and coenozoic eras.    

Fossils park of India –

1. Birbal sahni institute of palaeobotany, Lucknow.

2. 50 million year old fossil forests preserved in mandla district Madhya Pradesh.

3. 100 million year old fossil forest in rajmahal hills Bihar.

4. 260 million year old Coal forming forest in Orissa. 

 

Evidence of Evolution & Adaptive Radiation | Biology Class 12 - NEET

Evidence of Evolution & Adaptive Radiation | Biology Class 12 - NEET

Evidence of Evolution & Adaptive Radiation | Biology Class 12 - NEET

 

2.   Morphological and Anatomical Evidences – 

Different animals and plants show dissimilarities in their structure but in some characters they show similarities. These similarities are of two types.

1.  Homology
2. Analogy

1.   Homology – 

The similarity based on common origin, similar basic plan of organization and embryonic development is called homology. 

Similarity in appearance and function is not necessary. 

The organs which have common origin, embryonic development and same basic structure but perform different functions are called Homolgous organ. Homologous term given by Richard Owen.

Examples of Homologous organs –

Evidence of Evolution & Adaptive Radiation | Biology Class 12 - NEET

(i)   Forelimbs of mammals – 

 

Horse

Bat

Whale   

Seal   

Man 

Appearence

Foot

wings

Paddle       

  Flipper 

Hard

 Function

Running

Flying

Swimming   

Swimming    

Holding 

   

In their fore limbs similar bones are present like – humerus, radius, ulna, carplas, metacarpals and phalanges.

(ii)  Legs of invertebrates – 

Cockroach    - Honey bee

Walking    - Collecting of  pollens

But in both segmented legs are present are segments are same like coxa, Trochanter, Femur, tibia,  1-5 jointed tarsus.  

(iii)    Mouth parts of insects 

Cockroach         -        Honey Bee       -             Mosquito

Biting and chewing    -  Chewing and lapping    -  Piercing and sucking

In each of these insects the mouth parts comprise labrum, mandibles and maxillae.

(iv) Homology is also seen in the skeleton, heart, blood vessels and excretory system of different vertebrates.

(v) Thorn of Bougainvillea and tendril of cucurbita (Modification of axillary bud). 

(vi)  Wings of sparrow and pectoral fins of fish.

(vii) Hind limb of mammals.

(viii)  Potato & ginger.

(ix)  Radish & Carrot

(x) Homology is also seen among the molecule. This is called molecular homology. For example the proteins found in the blood of man and apes are similar.

(xi)    Testes in male and Ovaries in female develop from same embryonic tissue.

(xii)   Pectoral fin of fish and flipper of seal.

(xiii)  Flipper of penguin (bird ) and dolphin (mammal)

Divergent evolution (adaptive divergence/adaption radiation)   

Evidence of Evolution & Adaptive Radiation | Biology Class 12 - NEET

Homology found in different animals indicate their evolution from common ancestors.

Species which have diverged after origin from common ancestor giving rise to new species adapted to new habitats and ways of life is called adaptive radiation, exhibit large number of  homologous organs.

Homology shows Divergent evolution. 

For Example Adaptive radiation gave rise to a variety of marsupials in Australia.         

2.   Analogy – 

It is similarity in organs based on similar function.

Organs which have different origin and dissimilar fundamental structure but have similar function are called Analogous organs.

Evidence of Evolution & Adaptive Radiation | Biology Class 12 - NEET

Examples of Analogous organs – 

(i)   Wings of bat & birds are analogous to wings of insects.

(ii)   Pelvic fins of fish, flipper of seal

(iii)  Sting of bee and scorpion.

(iv)  Phylloclade of Ruscus and leaf

(v)   Chloragogen cell of pheretima and liver of  vertebrate

(vi)   Hands of man and trunk of elephant

(vii)  Potato and sweet potato.

(viii)  Eyes of Octopus and eyes of mammals (different in their retinal position).

(ix)   Dog fish and whale.

Convergent evolution (adaptive convergence/parallel evolution)

Development of similar adaptive functional structures in unrelated groups of organisms is called convergent evolution.  

For Example : Some of the marsupials of Australia resemble equivalent placental mammals that live in similar habitats of other continents.    

When adaptive convergence is found in closely related species, it is called parallel evolution.

Analogous organs do not show common ancestory but they show evolution.

Evidence of Evolution & Adaptive Radiation | Biology Class 12 - NEET

3.   Evidences from vestigial organs –

The organs which are present in reduced form and do not perform  any function in the body but correspond to the fully develop functional organs of related animals are called vestigial organs.

They are remnants of organs which were complete and functional in their ancestors.

Vestigial organs in Human body – 

Human body possess about 180 vestigial organs eg:- 

a.   nictitating membrane                                        
b.   muscles of pinna (auricular muscles)
c.   vermiform appendix                                            
d.   coccyx
e.  canine teeth                                                      
f.   third molars (wisdom teeth)
g.  segmental muscles of abdomen                          
h.  caecum
i.   body hairs                                                          
j.   nipples in male
k.  ear pinna                  

Vestigial organs in other animals – 

–    Hind limb and pelvic girdle of python

Evidence of Evolution & Adaptive Radiation | Biology Class 12 - NEET

–    wings of flightless birds such as ostrich, Emu, Kiwi, Dodo, Reha etc. (Dodo recently extinct)

–    Eyes of deep sea fishes

–    splint bones in feet of horse [2nd and 4th finger]

–    external ear in whale

–    rudiment of reptilian jaw apparatus.

–    Hind limb and pelvic girdle of whale.

Vestigial organs in plants – 

Scale leaves of Ruscus and various underground steams.

Vestigial organs are example of lamarckism (Theory of inheritance of acquired character) 

4.   Evidences from connecting links – 

Some animals and plants possess characters of two separate groups. One being primitive and the other is advanced group.

These species as bridge between two taxonomic groups such organism are called connecting link. They provide good example of organic evolution of common ancestory.

(i)      Virus : between living and non living

(ii)     Euglena : Between plants and animals

(iii)    Proterospongia : Between protozoa and porifera

(iv)    Neopilina : Between mollusca and annelida

(v)     Peripatus : Between Annelida and arthropoda

(vi)    Archaeopteryx : Between reptiles and birds

(vii)   Balanoglossus : Between non-chordates and chordates

(viii)  Chimera : Between cartilaginous fish and  Boney fish

(ix)    Lung fish (Protopterus) : Between fishes and amphibia

(x)     Platypus : Between reptiles and mammals

(xi)   Echidina : Between reptiles and mammals.

 

Evidence of Evolution & Adaptive Radiation | Biology Class 12 - NEET

 

5.   Evidences from Atavism (Reversion)  –

Sometimes in some individuals such characters suddenly appears which were supposed to be present in their ancestors but were lost during the course of development.

This phenomenon is known as atavism or reversion. Atavism proves that animals developing atavistic structure have evolved from such ancestors in which these structures were fully developed.

Evidence of Evolution & Adaptive Radiation | Biology Class 12 - NEET

Examples : 

1.   Human baby with tail 

2.   Cervical fistula – in some human babies an aperture is present on neck behind the ear called as cervical fistula. It represents pharyngeal gill slits which were present in aquatic vertebrate ancestors. 

3.   Long and pointed canine teeth represented carnivorous ancestors.   

4.   Large and thick body hair reflect our relationship with apes. 

5.   Extra nipples (more than two)       

6.   Evidence from physiology and biochemistry – 

Different organism show similarities in physiology and biochemistry. Some clear examples are :–

1.   Protoplasm : Structure and chemical composition of protoplasm is same from protozoa to mammalia.

2.   Enzymes : Enzymes perform same function in all animals like Trypsin digest protein from amoeba to man. Amylase digest starch from porifera to mammalia.  

3.   Blood : Chordates show almost same composition of  blood.

4.   ATP : This energy rich molecule is formed for biological oxidation in all animals.

5.   Hormones : Secreted in different vertebrates performs same function.

6.   Hereditary material : Hereditary material is DNA is all organism and its basic structure is same in all animals.

7.   Cytochrome C is a respiration protein situated in the mitochondria of all organism. In this protein from 78-88 A.A. are identical in all organism, which show common ancestory.

Physiology and biochemistry thus prove that all animals have evolved from some common ancestor.     

7.   Evidences from bio geographical distribution – 

The study of geographical distribution of animal and plant species in different parts of earth is called  Biogeography. 

Different animal species occurring in an area are called Fauna and those of plants are called Flora. 

On the basis of fauna and flora Alfred Russel Wallace divided the whole world into six major biogeographical regions called realms.

Nearctic : North America fro Mexixan highlands to Arctic islands and Greenland.

Palaearctic : Europe, North Asia up to Himalayas and North Africa up to Sahara desert.

Neotropical : Central and South America, Mexican lowlands and West Indies.

Oriental : Asia, South of Himalayas; India, Ceylon, Malay, Peninsula, Sumatra, Bornea, Java Celebes and Philippines.

Ethiopian : South Africa from Sahara Desert, Madagascar and Adjacent islands.  

Evidence of Evolution & Adaptive Radiation | Biology Class 12 - NEET

Australian : Australia, Tasmania, New Guinea, New Zealand and Oceanic islands of the pacific. It is believed that millions of years ago all the continents were present in the form of a single land mass called Pangaea.

Later on due to varies geological changes, these continents drifted fro one another.

As these continents moved away, they got separated from each other by the seas. As these continents had different environmental conditions so plants and animals evolved there were of different varieties. (New species).

Palaearctic and oriental realms are separated by high Himalayan Mountains.

1.   Prototheria – 

This is sub class of mammalian, which includes egg laying mammals like Platypus and Echidna found in Australia.

After the evolution of prototherians from reptiles Australia got separated from mainland of Asia.

Later on Eutherian mammals evolved in Asia, Due to their carnivorous nature they destroyed prototherians and metatherians from Asia.

So these groups became extinct on the mainland but they survived in Australia due to absence of Eutherians.

Today eutherians are also found in Australia (they were later transported by man).

2.   Marsupialia – The subclass of class mammalian includes kangaroos and Opossum which are found only in Australia.

3.   Darwin's finches – Darwin studied Fauna and Flora of Galapagos island situated near south America (consisted 22 islands). Here he saw 22 types of finches (birds) .

Evidence of Evolution & Adaptive Radiation | Biology Class 12 - NEET

A related species of these birds were also present in South American continent.

Probably some member of this species migrated to Galapagos island where these birds evolved into different species as a result of adaptation to environment.

These birds are now known as Darwin's Finches. 

Darwin described that a particular species is evolved in a particular area, progenies of this species migrate to different geographical areas and are gradually adapted to changing environmental conditions.

These adaptations gradually give rise to new species as a result of isolation.

Special Point :

a. Darwin's finches are also an example of adaptive radiation (different shape of beak and claws due to their habitat)

b. Darwin's finches are example of allopatric speciation.

4.   Elephants and lions are mainly found in Africa and India.

5.   Giraffe, Zebra and hippopotamus are found only in Africa. 

6.   Main land of human evolution in Africa.

Important Point : 

Palaeontological and Biogeographical evidences are considered as best evidences in support of organic evolution.  

8.   Evidences from Embryology – 

Baer's Law : An organism show its ancestor stages in embryonic development. In embryonic stage general characters appear first then specialized characters appear. 

Muller : First to propose 'Recapitulation theory'.

–    According to it 'ontogeny recapitulate phylogeny' it means any organism show its ancestral adult stages during its embryonic development.

It shows that all organism evolved from a common ancestor.

–    Ernest Haeckel explained it in detail and gave the name 'Biogenetic law'

Examples : - 

(i)   The Zygotes from which the development of all metazoan bodies starts, are single-celled and quite comparable with the Bodies of simple protozoans.

This indicates the origin of Metazoans from Protozoan Ancestors.

Evidence of Evolution & Adaptive Radiation | Biology Class 12 - NEET

(ii) The early stages of Embryonic development, Viz. Morula, Blastula and gastrula are Basically similar in all metazoans, indicating a Monophyletic Origin of the latter. 

 

(iii) The Phylogenetically earliest metazoans i.e., the sponges and cnidarians, have retained early gastrula like double – layered (Diploblastic) structure of Body of Metazoans.

(iv)    In fishes,  the young individual, developing from gastrula, is almost-like the adult, but the tadpole larvae of Amphibians bear more resemblance to the young once of fishes than to their own Adults. This indicates Origin of Amphibians from fishes.

(v)  Even after gastrulation in the vertebrates, the early postgastrula stages are quite similar in members of all the different classes, Viz, fishes, amphibians, reptiles, birds and mammals.

The differentiation of class characters appear in later stages, moreover, the embryo of phylogenetically higher vertebrates pass through the adult stages of lower vertebrates before finally attaining the characters of  their respective classes.

This proves that All Vertebrates have evolved from common fish like Ancestors and also that both Birds and mammals have evolved from reptiles.         

(vi) When the heart develops in the embryos of Amphibians, reptiles, Birds and Mammals, it is 2-chambered same as in the embryos and Adults of fishes. In later stages of Embryonic development in Amphibians, reptiles, the heart become, 3-chambered. In Birds and Mammals the heart is 4-chambered in the last embryonic stages to continue as such in the Adults.

(vii)   Modern Scientists have discovered ''Biochemical recapitulation'' also.

For example, fishes mainly excrete Ammonia. Adult Amphibians Excrete urea, but their tadpoles excrete Ammonia like the fishes.

Birds excrete uric acid, but their embryos excrete first Ammonia and then urea during earlier stages.

(viii)  In embryonic stage birds showed tooth buds for some time, which became extinct later. It show that birds evolved from toothed reptile like ancestors.

9.   Evidences from Taxonomy –            

Plants and Animals show a great diversity of form. They also show some similarities among themselves.

It is on account of these differences and resemblances that the taxonomists have to arrange them in to smaller and larger groups.

Among species also there are differences and resemblance of varying degree. Some species resemble one another more closely than they resemble others and form a closely related group.

Similarly, there are other groups of closely resembling species.

The members of each group resemble each other more closely than they resemble the members of other groups.

Each such group of species is called a genus. Genera also show different degrees of resemblances among themselves.

Those that resembles one another more closely than others are placed in a large group called a family.

Families are grouped in to larger units called orders, orders into classes and classes in to Phyla.

Evolution has a ready explanation for this system of grouping or classifying plants and animals in groups indicates relationship.

Special points  : - 

1.   The aquatic mammals [eg - Dolphins, Whales, Seals, Porpoises etc.] don't have gill slits because their adaptation to aquatic life is secondary.  

2.   In Acacia tree well developed compound leaves are found. But seedling has simple leaves like those found in all stages of development of its ancesters. This provide a good example of  Recapitulation

3.   Modern day Oaks of southern United State of America retain their foliage throughout  the year where as the oaks of northern United States are deciduous and shed their leaves during water. The southern species, on the basis of this character of leaves are considered to be more primitive than the northern oaks. However, the seedling of northern species are generally seen to retain their leaves during winter. This provide a good example of - Recapitulation

4.   EVOLUTIONARY TREND : 

The continuous change of a character within an evolving lineage is termed as evolutionary trend.   

THEORIES OF ORGANIC EVOLUTION

lamarckism :

First theory of evolution was proposed by

Jean Bapttiste de Lamarck (17-44 - 1829)

Book : Philosophie Zoologique (1809)

Lamarck coined the terms – Invertebrates, Annelida.

The term Biology was given by Lamarck & Treviranus.

  Evidence of Evolution & Adaptive Radiation | Biology Class 12 - NEET

Theory of Inheritance of Acquired Character

Basic Concept of Lamarckism–

(i)   Internal Vital Forces : 

Some internal forces are present in all organisms. By the presence of these forces organism have the tendency to increase the size of their organs or entire body.

(ii)  Effect of environment and new needs:

Environment influences all type of organisms. Changing environment gives rise to new needs. New needs or desires produce new structures and change habit of the organism.

(iii) Use and disuse of organs:

If an organ is constantly used, it would be better developed whereas disuse of organ result in its degeneration.

(iv) Inheritance of acquired character:

During the life of an organism new character develop due to internal vital forces, effect of environment, new needs and use and disuse of organs.

These acquired character are inherited from one generation to another. By continuous inheritance through many generation these acquired characters tend to make new generation quite different from its Ancestors resulting in the formation of new species.

 

Evidence of Evolution & Adaptive Radiation | Biology Class 12 - NEET

 

Example in support of Lamarckism : 

1.   Long neck and high fore limb of Giraffe. 

2.   Aquatic birds stretched their toes and developed web.     

3.   Snakes lost their legs.

4.   Deers became good runners by the development of strong limbs and streamlined body.

5.   Retractile claws of carnivorous animals

Criticism of Lamarckism - 

1.   According to first concept organism tends to increase their size but it is not universally true.

For Example among angiosperm the trees seem to be primitive and the shrubs, herbs and grasses have evolved from trees but the size was reduced during evolution.      

2.   Second concept is false. Can we sprout wings wishing to fly like birds.

3.   The third concept is some what true like the well developed biceps muscles of blacksmith and less developed wings in flight less birds.

But this concept also have many objections like the eyes of a student/reader do not increase in size and power with increasing age, the constantly beating heart maintains a constant size through generation.

4.   Fourth concept is completely false because acquired characters are not inherited.

–    Weismann

Weismann cut off the tails of rats for about 22 generations but there was no reduction in the size of tail on the basis of this experiment Weismann proposed the theory of continuity of germplasm.    

According to Weismann.

(i)    Two types of matters are present in organism, somatoplasm and germplasm.

(ii)   Sometoplasm in somatic cells and germplasm in Germinal cell.

(iii)   Somatoplasm dies with the death of organism while germaplasm transfers into the next generation.

(iv)  If any variation develops in germplasm, it is inherited , while if variation develop in somatoplasm it is not transmitted.

–    Pyane : Pyane kept drosophila in dark up to 69 generation, but there was no reduction in the size or sight of eyes

–    Boring of ear and nose in Indians.

–    Iron shoes of Chinese.

Neolamarckism-Term by Packard

Although Lamarckism remained controversial but some scientists gave the following evidences in favour of Lamarckism. The are known as neo-lamarckians.

According to neo lamarckism environment effected the inheritance of acquired character. According to it changing environment give rise some physical and chemical changes in organism, which effect their germplasm, and these acquired characters are definitely inherited.

1. Sumner's Experiment–

Sumner kept white rat in warn temperature resulting in elongation of body, large pinna and long tail. These features were inherited by the offspring.

2.  Kammerer's Experiment–

Kammerer kept salamander in dark background. The black spots found on skin were widely spread. In lighter, background the skin became yellow with limited black spots. These character were inherited by the offspring. 

3.  Mc Dugal's Experiment-

Mc Dugal trained white rats to cross a tank of water following a definite route. These trained rats were mated and their offspring were again trained. It was observed that there was decrease in the number of errors by offsprings of white rats.

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FAQs on Evidence of Evolution & Adaptive Radiation - Biology Class 12 - NEET

1. What is adaptive radiation in the context of evolution?
Adaptive radiation refers to the rapid diversification of a single ancestral species into multiple descendant species that occupy different ecological niches. This occurs when a species encounters new and diverse environments, leading to adaptations and specialization that enable them to exploit these new niches. In other words, it is the process by which a single species evolves into several distinct species, each suited to a specific environment or way of life.
2. What are some examples of adaptive radiation?
Some well-known examples of adaptive radiation include the finches of the Galapagos Islands, where different species evolved from a common ancestor and adapted to different diets and beak shapes depending on the available food sources. Another example is the cichlid fish in the African Great Lakes, where numerous species evolved unique adaptations to exploit different habitats and food resources. The Hawaiian honeycreepers, descended from a single ancestral finch-like bird, are another example of adaptive radiation, with each species having a specialized beak adapted to feed on various types of nectar, seeds, or insects.
3. How does adaptive radiation contribute to biodiversity?
Adaptive radiation plays a significant role in generating biodiversity. By allowing a single species to diversify and occupy various ecological niches, adaptive radiation leads to the formation of new species with distinct adaptations and characteristics. This process increases the overall number of species within a given ecosystem, thereby enhancing biodiversity. It also promotes ecological stability by reducing competition between closely related species as they specialize in different resources or habitats.
4. What are some factors that can trigger adaptive radiation?
Several factors can trigger adaptive radiation. One common trigger is the availability of new ecological opportunities or vacant niches. When a species encounters new habitats, resources, or environmental conditions, it can lead to adaptive radiation as individuals with specific traits that allow them to exploit these new opportunities have a higher fitness and reproductive success. Other factors that can contribute to adaptive radiation include the colonization of new areas, extinction events that create new vacant niches, and changes in environmental conditions over time.
5. How does the fossil record provide evidence for adaptive radiation?
The fossil record provides valuable evidence for adaptive radiation by documenting the existence of ancestral species and their subsequent diversification into multiple descendant species. Fossils of transitional forms can illustrate the gradual changes and adaptations that occurred during the process of adaptive radiation. By examining the fossil record, scientists can trace the evolutionary history of different lineages and identify patterns of diversification, providing insights into how adaptive radiation has shaped the diversity of life on Earth.
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