Eye: Human Organ Evolution Term Report

Introduction

The eye is a sensory system used throughout the kingdom animal . Indeed, the light giving a lot of information on the environment, it is, and has been a selective force majeure, which led to the formation of a wide variety of systems that perceive light(Pedrotti 12).

The definition of the eye varies according to biologists, with some considering that an eye is an organ capable of producing an image based on differences of intensities between photoreceptors . In this paper, the eye is defined in a broader sense, as the functional association of at least one photoreceptor cell and a cell pigment .

The evolution of the eye begins in the pre-Cambrian, while forming an opsin primitive origin of opsins in the eyes today, responsible for photoreception(Parker 41). The evolutionary radiation of the Cambrian is then marked by the convergent evolution of complex eyes in many branches formed at that time. The eyes thus formed have a wide variety of structures, including the way light is captured and concentrated. Subsequently, the eyes move under the influence of selective pressures of their environment, and change of habitat or lifestyle are often associated with significant changes in the structure and function of the eye.

Diversity of eyes

Approximately 1 / 3 of the 33 branches existing animals have photosensitive bodies, and another third has eyes, the last third having a priori no organs specialized in the detection of light. Today there is great diversity, both in the morphological structure, molecular anatomy of the eye or, as in the type of information collected from the light(Parker 45) .

Functional Diversity

The eyes, they all allow to collect and analyze the light, do not remove all the same information. In fact, can be analyzed:

Management, which requires different orientation of the pigments.

The intensity . All eyes are able to perceive light intensity. However, there is great variability in the sensitivity (minimum intensity perceived) quality and contrast (minimum difference of perceived intensity) in the animal kingdom(Grand 52).

The wavelength . While some eyes do not detect any of the wavelengths of incident light, many eyes are able to perceive colors. The perception of colors and contrasts varies greatly depending on the branch (even gender) considered.

The formation of an image. The concentration of pigments in an area of the retina , the fovea , allowing the formation of an image in some eyes. Only 6 phyla animals ( Cnidaria , themolluscs , the arthropods , and chordates , the annelids and onychophorans ) of 33 have eyes capable of forming images, but these lines are, alone, 96% of known animal species .Again, the resolution of the image formed varies greatly from one species to another(Land 74).

Structural diversity

All structures of the eye pose variability, sometimes associated with different functions:

There are many different pigments, composed of opsin (5 different classes in vertebrates) and a chromophore (2 different). The number of different pigments, and type of pigments present, differ between species and even between different photoreceptor cells of the same ...